,transcrib]'s ,notes3 ,text betwe5 und]scores repres5ts italics1 small capitals h be5 transcrib$ z ,,all ,,capitals4 ,curly brackets indicate subscripts2 lett]s betwe5 squ>e brackets 7su* z ,t & ,u7 repres5t ! %ape raht] ?an ! lett] itself4 ,m ,transcrib]'s ,notes may be f\nd at ! end ( ?is text4 ,,! ,,anatomy ,,( ,,bridgework ,,! ,,anatomy ,,( ,,bridgework ,,by ,,william ,,h5ry ,,?orpe ,,assoc4 ,m4 ,,in/4 ,c4 ,e4 ,,) #ajc ,,illu/rations ,illu/ration ,london ,e4 ,f4 ,n4 ,,spon1 ,,limit$1 #eg ,,haym>ket ,new ,york ,,spon ,,*amb]la91 #abc ,,lib]ty ,,/reet #aijf ,,preface ,9 (f]+ ?is little book to ! read] int]e/$ 9 ,bridgework1 ! au?or desires to express 8 ackn[l$gm5ts to ! proprietors ( 8,eng9e]+10 9 :i* j\rnal ! pap]s fir/ appe>$1 = _! c\rtesy 9 facilitat+ ! production 9 book =m4 ,x may possibly happ5 t ! scann+ ( ^! pages w induce o!rs to obs]ve & collect in=mation ext5d+ our k ( ?is subject--in=mation :i*1 :ile famili> to ma9t5ance eng9e]s ( exp]i5ce1 has n be5 s readily available z is desirable4 ,no !ory :i* fails to /& ! te/ ( practical work+ c ma9ta9 its claims to reg>d2 ! /udy ( ! behavi\r ( old "w has1 !re=e1 a high educational value1 & t5ds to ! occasional correction ( views :i* might o!rwise be complac5tly reta9$4 #fj ,,w9%am ,,/reet1 ,,clapham ,,common1 ,,london1 ,s4,w4 ,octob]1 #aijf4 ,,cont5ts ,,*apt] ,i4 ,,introduction--,,gird] ,,be>+s4 ,,page ,pressure di/ribution--,squ>e & skew be>+s--,fix$ be>+s-- ,knuckles--,roll]s--,yield ( supports #a ,,*apt] ,,ii4 ,,ma9 ,,gird]s4 ,plate webs3 ,improp] load+ ( flanges--,twi/+ ( gird]s-- ,rem$ial measures--,cracks 9 webs--,/iff5+ ( webs--,t /iff5]s #i ,op5 webs3 ,common faults--,top booms--,buckl+ ( bottom booms-- ,c\nt]brac+--,flat memb]s #ag ,,*apt] ,,iii4 ,,bridge ,,floors4 ,liability to defects--,impact--,ends ( cross & longitud9al gird]s--,awkw>d rivet+--,fix$ ends to cross gird]s--,plat$ floor--,lib]al dep?s desirable--,type connections--,effect ( 8skew0 on floor--,wat]-tightness--,dra9age--,timb] floors--,jack ar*es-- ,corrugat$ %eet+--,balla/--,rail jo9ts--,effect ( ma9 gird]s on floors #bj ,,*apt] ,,iv4 ,,brac+4 ,effect ( brac+ on gird]s--,influ5ce ( skew on brac+--,flat b>s--,ov]head gird]s--,ma9 gird]s /iff5$ f floor-- ,/iff5+ ( light gird]s--,incomplete brac+--,tall pi]s--,sea pi]s #cd ,,*apt] ,v4 ,,rivet$ ,,connections4 ,latitude 9 practice--,laboratory exp]im5ts--,c>e 9 consid]+ practical in/ances--,ma9 gird] web rivets--,lattice gird]s inve/igat$--,rivets 9 small gird]s--,faulty bridge floor-- ,/resses 9 rivets--,cross gird] connections--,t5sion 9 rivets-- ,defective rivets--,loose rivets--,table ( actual rivet /resses-- ,be>+ pressure--,p]missible /resses--,propos$ table--,immunity ( road bridges f loose rivets--,rivet spac+ #de ,,*apt] ,,vi4 ,,high ,,/ress4 ,ela/ic limit--,c>e 9 calculation--,impact--,examples ( high /ress --,e>ly examples ( high /ress 9 /eel gird]s--,tabulat$ examples--,g5]al rem>ks #fa ,,*apt] ,,vii4 ,,de=mations4 ,v>i\s k9ds--,flex+ ( gird] flanges--,examples--,settlem5t de=mations--,creep+--,temp]ature *anges--,local di/ortions-- ,imp]fect workman%ip--,de=mation ( ca/-iron ar*es #gc ,,*apt] ,,viii4 ,,deflections4 ,diff]5ces z betwe5 new "w & old--,influ5ce ( booms & web /ructure on deflection--,yield ( rivets & /iffness ( connections--,work+ =mul--,set--,effect ( floor sy/em-- ,deflection diagrams--,loads quickly appli$--8,drop0 loads--,flexible gird]s--,measur+ deflections--,new me?od ( obs]v+ deflections --,effect ( runn+ load #he ,,*apt] ,,ix4 ,,decay ,,& ,,pa9t+4 ,examples ( ru/+ ( wr\ght-iron gird]s--,gird] ov] sea-wat] --,rate ( ru/+--,/eelwork--,precautions--,r$-lead- -,repa9t+-- ,scrap+--,gird]s built into masonry--,ca/ iron--,effect ( sea- wat] on ca/ iron--,examples--,tabulat$ obs]vations--,p]c5tage ( subm]sion--,quality ( metal #if ,,*apt] ,x4 ,,exam9ation1 ,,repair1 ,,& ,,/r5g!n+ ,,( ,,rivet$ ,,bridges4 ,purpose--,me?ods ( exam9ation--,calculations--,/ress 9 old "w-- ,me?ods ( r$uc+ /ress--,repair--,loose rivets--,replac+ wa/$ flange plates--,add+ new to old sections--,pr9ciples gov]n+ additions--,example--,/r5g!n+ lattice gird] brac+s--,brac+ betwe5 gird]s--,/r5g!n+ floors--,di/ribut+ gird]s #ajg ,,*apt] ,,xi4 ,,/r5g!n+ ,,( ,,rivet$ ,,bridges ,,by ,,c5tre ,,gird]s4 ,pr9cipal me?ods 9 use--,me?od ( calculation--,adju/m5ts-- ,connections--,me?od ( execution--,*ecks--,effect ( skew on me?od consid]$--,results ( calculation = a typical case--,probable error--,practical examples--,special case--,me?od ( det]m9+ flexure curves #abb ,,*apt] ,,xii4 ,,ca/-,,iron ,,bridges4 ,limitations ( ca/ iron--,/ress examples--,advantages & disadvantages--,f\ndry /resses--,examples--,want ( ductility ( ca/ iron--,repairs--,re/rict$ possibilities #ada ,,*apt] ,,xiii4 ,,timb] ,,bridges4 ,p]i%able nature--,causes ( decay--,sag--,lat]al brac+--,piles-- ,unc]ta9ty respect+ decay--,examples--,conditions & practice fav\rable to durability--,brac+--,protection--,repair --,piles--,co/ #adi ,,*apt] ,,xiv4 ,,masonry ,,bridges4 ,def9ition--,cause ( defects or failure--,spread+ ( abutm5ts-- ,clos+ 9--,example--,/op pi]s--,example ( failure--,/r5g? ( rubble ar*--,equilibrium ( ar*es--,effect ( vibration on masonry --,safety c5tr+--,me?ods ( repair--,po9t+--,r\gh dress$ /onework #aeg ,,*apt] ,,xv4 ,,life ,,( ,,bridges--,,relative ,,m]its4 ,previ\s hi/ory--,causes ( limit$ life--,tabulat$ examples ( %ort-liv$ metallic bridges--,timb] & masonry bridges-- ,durability--,ma9t5ance *>ges--,fir/ co/--,comp>ative m]its-- ,*oice ( mat]ial #afe ,,*apt] ,,xvi4 ,,recon/ruction ,,& ,,wid5+ ,,( ,,bridges4 ,,conclusion4 ,measur+ up--,railway "u-bridges--,me?ods ( recon/ruction 9 common use--,recon/ruction ( bridges ( _m op5+s--,timb] /ag+--,traffic arrangem5ts--,sunday "w--,railway ov]-bridges-- ,wid5+s--,junction ( new & old "w--,conclud+ rem>ks--,/udy ( old bridgework #agb ,,index #ahg ,,! ,,anatomy ,,( ,,bridgework4 ,,*apt] ,i4 ,,introduction4 ,no book has1 s f> z ! au?or is aw>e1 be5 writt5 ^u t aspect ( bridgework to be treat$ 9 ! foll[+ pages4 ,no excuse ne$1 !re=e1 be giv5 = add+ to ! already l>ge am\nt ( publi%$ matt] deal+ ) bridges4 ,inde$1 z x too (t5 happ5s t ! design+ ( su* con/ructions1 & _! aft]-ma9t5ance1 are 9 ?is c\ntry entirely sep>at$1 x _c b be useful to give su* results ( ! behavi\r ( bridges1 :e!r new or old1 z h come "u obs]vation4 ,9 ! e>ly days ( metallic bridges !re 0 ( necessity no exp]i5ce available to guide ! eng9e] 9 8 endeav\r to avoid objectionable features 9 design1 & he 01 z a result1 compell$ to rely ^u 8 own =esight & judgm5t 9 any attempt to anticipate ! effects ( ^? influ5ces to :i* 8 "w might lat] be subject4 ,h[ heavily h&icapp$ he mu/ h be5 "u ^! conditions is evid5t f ! mass ( in=mation s9ce acquir$ by ! exp]im5tal /udy ( ! behavi\r ( metals "u /ress1 & ! gr[? ( ! lit]ature ( bridgework dur+ ! la/ =ty ye>s4 ,t _m mi/akes 7 made is little occasion = surprise2 r is x a cause = admiration t "s v f9e bridges1 /ill 9 use1 7 ! product ( t "t4 ,mu* may be le>n$ f ! /udy ( defects & failures1 ev5 ?\gh !y be ( su* a "* t no exp]i5c$ design] w\ld n[ furni% l examples4 ,mod]n in/ances may1 none ! less1 be f\nd1 ) faults repeat$1 :i* %\ld long s9ce h disappe>$ f all bridgework1 & are only to be acc\nt$ = by ! unnatural divorce ( design & ma9t5ance already ref]r$ to4 ,z ! read] proce$s1 x may appe> t details are occasionally t\*$ ^u ( a "* altoge!r too crude & objectionable to ne$ comm5t2 b ! consid]ation ( ^! cases is none ! less int]e/+1 &1 s f> z ! au?or's obs]vation goes1 n altoge!r unnecess>y4 ,mo/ ( ! in/ances cit$ are ( bridges1 or p>ts ( bridges1 ( q small dim5sions2 b x is ^! :i* mo/ commonly give tr\ble1 bo? because ! effects ( impact are 9 su* cases mo/ sev]ely felt1 & possibly because ! small] class ( bridges is v g5]ally design$ by m5 ( less exp]i5ce1 ?an l>ge & impos+ /ructures4 ,! p>ticul>s giv5 relate 9 all cases to bridges ( wr\ght iron1 unless o!rwise describ$4 ,an endeav\r has be5 made to secure "s k9d ( ord] 9 deal+ ) ! subject1 b x has be5 f\nd difficult to avoid a some:at disjo9t$ treatm5t1 insep>able1 p]haps1 f ! nature ( ! matt]4 ,f9ally1 ! read] may be assur$ t e case quot$ has come "u ! writ]'s p]sonal notice4 ,,gird] ,,be>+s4 ,9 gird]-"w g5]ally1 & m p>ticul>ly 9 plate-gird]s1 consid]able latitude obta9s 9 ! am\nt ( be>+ all[$4 ,cle>ly1 ! surface ov] :i* ! pressure is di/ribut$ %\ld be suffici5tly ample to avoid ov]load+ & possible cru%+ or fracture ( b$/ones :]e ^! exi/2 b if no knuckles are introduc$1 ?is is an extremely difficult matt] to insure4 ,a long be>+ may deliv] ! load at ! extreme end ( ! surface on :i* x re/s1 or1 m probably1 ne> ! face4 ,if ! gird] is made ) truly level be>+s1 & ! b$s set level1 x w c]ta9ly1 :5 "u load1 ?r[ an extreme pressure ^u t "p ( ! be>+ surface imm$iately "u ! =w>d edge ( ! be>+-plate4 ,^! consid]ations probably acc\nt = b$/ones frequ5tly crack+1 9 addition to :i* possibility !re is ! disadvantage t ! design] does n "k :]e ! gird] w re/1 & _c truly def9e ! span4 ,! v>iation ( flange-/ress due to ?is cause may1 9 a gird] ( ord9>y proportions1 hav+ be>+s equal 9 l5g? to ! gird]'s dep?1 be z mu* z #ae p] c5t4 above or bel[ t int5d$4 ,if great c>e be tak5 9 sett+ b$s1 9 ! fir/ in/ance1 to dip t[>d ! c5tre ( ! span an am\nt dep5d+ ^u ! anticipat$ gird] deflection1 x may be possible to insure t :5 "u full load ! gird] be>+ %all re/ equally ^u its seat2 b ?is is evid5tly a difficult condition to obta9 practically1 is good only = "o degree ( load+1 & may at any "t be nullifi$ by a di/urbance ( ! supports1 z1 = in/ance1 ! v common occurr5ce ( a slight lean+ =w>d ( abutm5t walls4 ,d\ble or treble ?icknesses ( hair-felt are sometimes plac$ b5ea? gird] be>+s1 ) ! object ( secur+ a bett] di/ribution ( pressure1 no d\bt ) advantage2 b ?is practice1 ?\gh x may be q satisfactory z appli$ to gird]s c>ry+ an un*angeable load1 h>dly meets ! case = loads :i* are v>iable4 ,not)/&+ ! faulty nature ( ! pla9 be>+ ord9>ily us$ = gird]s ( mod]ate span1 its extreme simplicity comm5ds x to mo/ eng9e]s4 ,x mu/ be admitt$ t no s]i\s inconv5i5ce ne$ be anticipat$ 9 ! majority ( cases1 p>ticul>ly if ! be>+s are limit$ 9 l5g?1 d n approa* ne>] ?an #c in*es to ! face ( b$/ones1 & are furni%$ ) hair-felt or simil> pack+4 ,illu/ration3 ,,fig4 #a4 ,:e!r ) long or %ort be>+s1 ! =w>d edge %\ld be at "r angles to ! gird]'s l5g?4 ,9 skew bridges x is sometimes se5 t ?is edge foll[s ! angle ( skew4 ,! effect on ! gird] is to twi/ x1 z w be cle> f a little consid]ation4 ,9 evid5ce ( ?is ! case may be quot$ ( a lattice gird] ( #ie feet effective span & #g feet deep1 :i*1 re/+ on a skew abutm5t "r up to ! masonry face at a r bad angle 7ab\t #ae degrees71 01 aft] tw5ty ye>s1 f\nd cant$ ov] at ! top to ! ext5t ( #d in*es1 ) ! fur!r result ( spr++ a jo9t 9 ! top flange at ab\t ! middle ( ! gird]1 caus+ "s rivets to loos54 ,! b$/one 0 also v badly brok5 at ! face1 & _h to be replac$ 9 ! c\rse ( repairs 7,fig4 #a74 ,?is gird] _h1 9 addition to ! cant+ f ! upright position at its end1 & ! di/ortion ( ! top flange1 a curvature 9 ! same direction1 ?\gh less 9 am\nt1 at ! bottom--an effect v common 9 ! ma9 gird]s ( skew bridges1 & possibly acc\nt$ = 9 "p by a t5d5cy ( ! gird] end to creep along ! abutm5t away f ! po9t at :i* x be>s h>de/1 "u frequ5t applications & removals ( ! live load1 & accompany+ deflections4 ,?is t5d5cy to travel may be aggravat$ 9 bridges c>ry+ a balla/$ road1 9 :i* !re may be a consid]able ?ickness ( balla/ ne> ! be>+s1 by ! compact+ & spread+ ( ?is mat]ial tak+ effect ^u ! gird] end1 t5d+ to pu% x outw>ds1 be+ ti$ only by a few light cross-gird]s badly plac$ = useful effect4 ,! movem5t may be prev5t$ 9 new "w = mod]ate angles ( skew by c>ry+ ! end cross-gird]s well back1 & secur+ !m 9 "s effici5t mann]2 or by ! introduction ( a diagonal tie foll[+ ! skew face1 & atta*$ to cross & ma9 gird] flanges 7,fig4 #b7--;a me?od :i* may be appli$ to exi/+ "w also4 ,illu/ration3 ,,fig4 #b4 ,= su* a case z t cit$ x is imp]ative t balla/ pressure at ! gird] end %\ld be altoge!r elim9at$4 ,! fix+ ( gird] ends by bolts--a practice at "o "t usual--h>dly calls = rem>k1 z x is n[ seldom resort$ to unless = special reasons2 b x may be well to po9t out ! weak5+ effect ( holes = any purpose 9 b$/ones4 ,b$-plates commonly ne$ no fix+2 ! weight c>ri$ keeps !m 9 position1 or if1 9 ! case ( v light gird]s ^u sep>ate plates1 x is consid]$ well to secure ^! f %ift+1 x may be/ be done by lett+ ! plate 9 bodily a small am\nt1 or by means ( a v %all[ fea!r sunk into a *ase4 ,illu/ration3 ,,fig4 #c4 ,z an improvem5t ^u ! pla9 be>+ usually adopt$1 x is an easy matt] s to design gird]-ends z to deliv] ! load by a n>r[ /rip ( be>+-plate c>ri$ across ! bottom flange1 di/ribut+ ! pressure ^u ! /one1 if !re be "o1 by means ( a simple rectangul> plate ( suffici5t /\tness 7,fig4 #c74 ,an imp]fect knuckle w by ?is means result1 ) fre$om to slide1 & ! gird] span be def9$ )9 n>r[ limits4 ,a true knuckle is1 ( c\rse1 ! be/ means ( secur+ imposition ( ! load always 9 ! same place2 b ?is by itself is n suffici5t :]e ! gird] is ( a l5g? to make temp]ature & /ress v>iations important1 9 :i* case roll]s1 or fre$om to slide1 become necess>y4 ,bridges exi/ 9 :i* roll]-be>+s h be5 adopt$ )\t ! knuckle1 or its equival5t1 b ?is is :olly indef5sible1 z x is obvi\s t ! =w>d roll] w 9 all probability take ! :ole load1 & _c be expect$ to keep its %ape & roll freely "u ?is mal-treatm5t4 ,x is sometimes ass]t$ t roll]s are nev] effective aft] "s ye>s' use2 t !y become clogg$ ) dirt1 & refuse to p]=m _! (fice4 ,!re is no reason :y roll]s %\ld n be box$ 9 to exclude dirt by a cas+ easily remov$1 "s att5tion be+ giv5 to !m1 & any possible accumulation ( dirt remov$ ea* "t ! bridge is pa9t$4 ,to te/ ! behavi\r ( roll]s "u some:at unfav\rable conditions = _! prop] action--t ( ! be>+s ( ma9 ro( trusses ( cresc5t =m1 #aij feet span--! au?or1 "s ?irty ye>s s9ce1 took occasion to make ! necess>y obs]vations1 & f\nd evid5ce ( a mod]ate roll] movem5t1 ?\gh !re 0 9 ?is case no direct horizontal memb] to communicate motion4 ,) gird]s re/+ ^u columns1 p>ticul>ly if ( ca/ iron1 a roll] & knuckle arrangem5t is mo/ desirable = any b v small spans1 z1 if n adopt$1 ! result w be a cant+ ( ! columns f side to side--a v small am\nt1 x is true1 b suffici5t to ?r[ ! load ^u ! extreme edges ( ! base1 ?\gh ! knuckle alone w relieve ! top ( ?is dang]4 ,! au?or at "o "t took ! tr\ble to exam9e1 s f> z x c\ld be done sup]ficially & )\t op5+ out ! gr\nd to make a complete inspection possible1 a numb] ( bridges cross+ /reets1 9 :i* gird]s re/$ ^u & 7 secur$ to ca/-iron columns /&+ 9 ! l9e ( k]b2 & he f\nd cracks1 ei!r at ! top or bottom1 9 ab\t "o ( e f\r columns4 ,:5 gird]s pass+ ov] columns are n cont9u\s1 x may be difficult to f9d room = a d\ble roll] & knuckle arrangem5t2 b ?is inconv5i5ce may be ov]come by c>ry+ "o gird]-end :olly across ! column-top1 & secur+ ! next gird]-end to x 9 a mann] :i* a little c>e & +5uity w r5d] satisfactory1 "o free be>+ !n s]v+ to c>ry ! load f bo? gird]s4 ,?\gh ! wisdom ( us+ roll]s is app>5t 9 spans exce$+ "s mod]ate l5g?1 say #hj feet--z to :i* eng9e]s d n seem q decid$--& v>y+ ) ! conditions1 x ne$ n be ov]look$ t 9 "s cases masonry w be suffici5tly accommodat+ to r5d] !m unnecess>y2 pi]s1 if suffici5tly tall & sl5d]1 w yield a small am\nt )\t injury1 & ?\gh %ort]1 if re/+ ^u a bottom n absolutely rigid1 w rock & give ! necess>y relief2 b x is obvi\s1 if ! resi/ance to movem5t is suffici5tly great1 & ! gird] _c slide or roll on its be>+s1 b$/ones w probably loos51 z1 inde$1 frequ5tly happ5s4 ,,*apt] ,,ii4 ,,ma9 ,,gird]s2 ,,plate-,,webs4 ,x is seldom t gird]s ( ?is description--or1 inde$1 ( any o!r--%[ signs ( failure f m]e defect ( /r5g? 9 ! pr9cipal p>ts1 ev5 ?\gh some:at highly /ress$2 & in/ances t5d+ to support ?is /atem5t w be giv5 9 a lat] *apt]4 ,= ! pres5t1 x is propos$ to indicate peculi>ities ( behavi\r only1 g5]ally1 b n always1 h>mless4 ,?\gh n[ less (t5 done1 x 0 at "o "t common practice to load plate-gird]s on ! bottom flange by simply re/+ floor timb]s1 rails1 tr\ghs1 or cross-gird]s ^u !m4 ,9 outside gird]s "o result ( ?is is to cause ! top flange to take a curve 9 plan1 convex t[>ds ! road1 e "t ! live load comes ^u ! floor ( ! bridge1 ^u ! pass+ ( :i* ! flange resumes its figure1 ?\gh /ill affect$ by t "p ( ! load :i* is con/ant4 ,a bridge ( #dg feet span1 c>ry+ two l9es ( way1 hav+ "o c5tre & two outside gird]s1 ) a floor consi/+ ( old ,b>l[ rails1 re/+ ^u ! bottom flanges1 %[$ ! peculi>ity nam$ 9 a m>k$ degree4 ,! outside gird]s1 "u dead load only1 71 z to ! top flanges 7see ,figs4 #d & #e71 #a-a_/d in* & #a-a_/af in* respectively out ( /raight 9 _! l5g?1 b ^u ! pass+ ( a goods eng9e & tra9 curv$ an additional #a-a_/h in*1 or #b-c_/h in*es 9 all1 = "o outside gird]1 & #b-c_/af in*es = ! o!r4 ,! c5tre gird]1 hav+ a broad] & heavi] top flange1 curv$ #e_/h in* t[>ds :i*ev] road might be load$4 ,! effect ( su* horizontal flexure is cle>ly to induce /resses ( t5sion & compression 9 ! flanges1 :i*1 be+ 7= ! top flange7 comp\nd$ ) ! normal compressive /ress due to load c>ri$1 results 9 a consid]able want ( uni=mity across ! section4 ,illu/ration3 ,,fig4 #d4 ,9 ! case "u notice1 ! writ] e/imates ! /resses = an out] gird] top flange at #de tons p] squ>e in* compression = simple load+1 & #ee tons p] squ>e in* ( t5sion & compression1 on ! inn] & out] edges1 due to flexure1 result+ :5 comp\nd$ 9 a /ress ( #a ton p] squ>e in* t5sion on ! inside1 & #aj tons p] squ>e in* compression on ! outside edge4 ,9 ?is r extreme case ! /ress on ! inn] edge1 or t ne>e/ ! load1 is rev]s$ 9 "*4 ,! effect describ$ appe>s to be n :olly due to ! twi/+ mom5t4 ,x is app>5t t :atev] curvature may be induc$ by twi/+ alone mu/ be aggravat$ 9 ! compression flange by its be+ put out ( l9e4 ,! writ] does n attempt "h to apportion ! two effects 9 any o!r way ?an to say t ! great] "p ( ! flexure appe>s to be due to ! second>y cause4 ,consi/5t ) ?is view ( ! matt] is ! fact t ! incl9ation ( ! gird] t[>ds ! rails greatly exce$$ ! calculat$ slope ( ! ,b>l[ rail-ends :5 "u load1 be+ ab\t five times z great4 ,! inf]5ce is t ! floor rails bore h>d at _! extreme ends1 at :i* po9t ( be>+ ! calculat$ twi/+ mom5t acc\nts = less ?an "o-half ( ! flexure obs]v$ 9 ! flanges4 ,illu/ration3 ,,fig4 #e4 ,! gird]s ^u removal 9 ! c\rse ( recon/ruction aga9 took ! /raight =m1 %[+ t ! v frequ5t developm5t ( ! /resses nam$ _h n s5sibly injur$ ! metal1 ?\gh ! bridge c>ri$ z _m z ?ree hundr$ tra9s daily 9 ea* direction1 & _h done s = v _m ye>s4 ,! de=mation ( ! top flange only has be5 notic$1 yet ! same t5d5cy exi/s 9 ! bottom1 ?\gh ! actual am\nt is mu* less1 bo? because ! l[] flanges are 9 t5sion1 & are also 9 great degree conf9$ by ! frictional contact ( ! cross be>]s1 ev5 :]e no prop] ties are us$4 ,9 ! case dealt ) ! bottom flanges ( ! out] gird]s curv$ #a_/h in* outw>ds only4 ,) ! broad flanges commonly adopt$ 9 ,engli% practice1 twi/+ ( ! gird]s1 "u conditions simil> to ! above1 w n g5]ally be a s]i\s matt]2 b ) n>r[ flanges possess+ little lat]al /iffness x might be a s\rce ( dang]4 ,illu/ration3 ,,fig4 #f4 ,,fig4 #g4 ,! twi/+ may be limit$ 9 am\nt by introduc+ a cross-frame betwe5 ! gird]s1 f :i* !y are /iff5$2 by /rutt+ ! gird]s imm$iately f ! floor itself1 9 :i* case !y _c cant to a great] ext5t ?an t :i* corresponds to ! floor deflection2 or by design+ ! top flange to be unsymmetrical ) ref]5ce to ! web1 z 9 ,figs4 #f & #g1 ) ! object ( insur+ t "u ! jo9t effect ( v]tical load+ & twi/+1 ! /ress 9 ! flange %all at maximum loads be uni=m across ! section1 & all[ x to rema9 /raight4 ,?is may be secur$ by mak+ ! ecc5tricity ( ! flange section equal to t ( ! load+4 ,= in/ance1 if ! load be appli$ #c in*es away f ! web c5tre1 ! flange %\ld h its c5tre ( gravity #c in*es on ! o!r side ( ! c5tre l9e4 ,x c be %[n t ?is is true ?r\gh\t ! l5g? ( ! gird]1 & irrespective ( ! dep?4 ,an in/ance 9 :i* flange ecc5tricity be+ 9 excess1 curvature outw>ds result$1 w be f\nd 9 a lat] *apt] on de=mations1 etc4 ,x w n g5]ally be necess>y to make ! bottom flange ecc5tric1 z x is commonly ti$ 9 "s way2 b if done1 ! ecc5tricity %\ld be on ! same side z = ! top4 ,! flanges rema9+ /raight "u ^! conditions are n subject to ! complications ( /ress ref]r$ to 9 ! case fir/ quot$4 ,! au?or has adopt$ bo? ! la/ nam$ details 9 bridges :]e he has be5 oblig$ to accept unfair load+ ( ! k9d discuss$4 ,x %\ld be rem>k$ t by ! two fir/ me?ods1 if ! /iff5+ frames are wide ap>t & atta*$ direct to ! web1 !re is a liability = ?is to te>1 "u di/ress1 r ?an keep ! gird] 9 l9e4 ,!re is "o o!r possible consequ5ce ( ?r[+ load ^u ! flanges ( a gird] ( a mu* m al>m+ nature4 ,9 gird]s n v well /iff5$1 x may happ5 t ! frequ5t application ( load 9 ?is mann] f9ally s injures ! web-plate1 j above ! top edge ( ! bottom angle-b>s1 z to cause x to rip 9 a horizontal direction4 ,m likely is ?is to happ5 ) a c5tre gird] tak+ load fir/ on "o side1 !n on ! o!r1 & aga9 on bo? toge!r4 ,cases may be cit$ 9 :i* cracks "r ?r\gh ! webs #c feet or m 9 l5g? h result$ f ?is cause4 ,x is v probable1 h[ev]1 t 9 "s ( ^! cases ! matt] 0 aggravat$ by ! use ( a poor iron 9 ! webs1 z at "o "t eng9e]s1 f mi/ak5 notions ( ! extreme t5uity p]missible 9 webs ne> ! c5tre ( a gird]1 w\ld1 if !y c\ld n be made ?9 en\gh1 ev5 enc\rage ! use ( an indiff]5t metal z be+ q good en\gh = t "p ( ! "w4 ,an in/ance ( web-fracture f some:at simil> causes may be "h giv54 ,9 a bridge ( #ca feet #f in*es effective span1 & consi/+ ( tw9 gird]s c>ry+ rails betwe51 z %[n 9 ,figs4 #h & #i1 ! load re/+ ^u ! inn] l$ges1 =m$ by ! bottom flange1 induc$ su* a b5d+ & te>+ action along ! web j above ! angle-b>s1 z to cause a rip 9 "o ( ! gird]s1 well op5 = "s di/ance1 & :i* c\ld be trac$ = #ad feet z a cont9u\s crack4 ,illu/ration3 ,,fig4 #h4 ,illu/ration3 ,,fig4 #i4 ,x w be notic$ 9 ! figure t ! ,t /iff5]s occur only at ! out] face ( ! web1 & t ! inn] v]tical /rips /op %ort at ! top edge ( ! angles1 ! result be+ t "u load ! flange w\ld t5d to twi/ ar\nd "s po9t1 say ,a1 at ea* /iff5]1 induc+ a s]i\s /ress 9 ! ?9 web at t place1 :ile away f ^! /iff5]s ! web w\ld be m free to yield )\t te>+4 ,! fact t at a numb] ( ! /iff5]s incipi5t cracks 7 obs]v$1 "s only a few in*es long1 sugge/s ?is view ( ! matt]4 ,a case ( web-failure f o!r influ5ces com+ "u notice %[$ breaks at ! upp] "p ( ! web ext5d+ d[nw>ds4 ,9 ?is bridge1 ( #cb feet span1 :i* _h be5 9 exi/5ce ?irty-two ye>s1 ! webs--orig9ally #a_/d in* ?ick--71 l>gely because ( c9d] balla/ 9 contact ) !m1 s badly wa/$ z to be g5]ally little ?ick] ?an a cr[n-piece1 & 9 places 7 eat5 ?r\gh2 9 addition to :i*1 ! road be+ on a %>p curve1 ! rail-balks _h be5 /rutt$ f ! webs to keep !m 9 position1 ! effect ( :i* w\ld be to ex]t a hamm]+ ?ru/ ^u ! face ( ! web at ! abutt+ ends1 & assi/ 9 />t+ cracks 9 webs already mu* corrod$4 ,a feature ( ?is case1 t5d+ to %[ t ! breaks result$ z ! jo9t effect ( wa/e & ill-usage by ! /rut memb]s1 r ?an by excessive /ress 9 ! web z r$uc$1 is to be f\nd 9 ! fact t ! gird]s :5 remov$ 7 obs]v$ to be 9 rem>kably good %ape--i4e4 ! camb]1 m>k$ on ! orig9al draw+s to be #a-a_/b in*1 /ill %[$ z a p]fectly ev5 curve ( t rise1 :i* w\ld h>dly h be5 ! case if ! l[] flange _h be5 let d[n by web-rupture1 ! result ( excessive web-/resses4 ,occasionally webs w crack ?r\gh ! solid unwa/$ plate1 9 a l9e ne>ly v]tical2 n :]e %e> /ress is greate/1 b g5]ally at "s o!r place1 & f no app>5t cause1 ei!r ( /ress or ill-usage4 ,! writ] has obs]v$ ?is only 9 ! case ( small gird]s n exce$+ #b feet 9 dep?2 &1 = want ( any bett] reason1 attributes ^! cracks to poor mat]ial1 c\pl$ ) "s lat5t defect4 ,9 a bridge hav+ "s ?irty cross-gird]s1 ea* #bf feet long1 ab\t e o!r "o _h a web crack$ 9 ?is mann] aft] _m ye>s' use4 ,web-cracks ( ! k9d fir/ indicat$1 are p]haps1 ! mo/ probable s\rce ( dang] 9 plate-gird]s1 ( any :i* are likely to occur4 ,! fault is insidi\s1 difficult to detect :5 fir/ develop$1 & p]haps n se5 at all till ! bridge1 condemn$ = "s o!r reason1 has ! gird]s freely expos$ & br\ght into broad light4 ,! mann] 9 :i* old gird]s are sometimes p>tly conceal$ by timb]work1 or cov]$ by balla/1 makes ! detection ( ^! defects an unc]ta9 matt]1 unless suffici5t tr\ble is occasionally tak5 to r5d] inspection complete4 ,! mann] 9 :i* gird]s ) wa/$ & fractur$ webs w /ill hang toge!r "u heavy load+ seems to w>rant ! d$uction t1 9 design+ new "w1 x c h>dly be necess>y to provide su* a consid]able am\nt ( web-/iff5+ z is sometimes se52 exp]i5ce %[+ t defects ( ! web-/ructure d n commonly occur 9 ! /iff5+ s frequ5tly z 9 ! plate1 & !n 9 ! =m ( cracks4 ,a case ( web-buckl+ lies1 s f>1 )\t ! au?or's exp]i5ce4 ,!re is no ne$ to introduce1 = web-/resses alone1 m /iff5+ ?an t :i* corresponds to mak+ ! /iff5]s d duty z v]tical /ruts 9 an op5work gird]2 9 :i* case x is suffici5t to insure t ! /iff5]s occurr+ 9 a l5g? equal to ! gird]'s dep? %all1 z /ruts1 be /rong en\gh 9 ! aggregate to take ! :ole %e> =ce at ! section consid]$1 9 no case exce$+ ?is am\nt on "o /iff5]4 ,= ?9 webs 9 :i* ! free bread? is great] ?an "o hundr$ & tw5ty times ! ?ickness1 ! diagonal compressive /ress may be completely ignor$1 & ! ?ickness det]m9$ ) ref]5ce to ! diagonal t5sion /ress only4 ,!re is "o fault :i* frequ5tly %[s itself 9 /iff5]s ?\gh n ! result ( web-/resses1 & :5 p]=m+ an additional function--viz41 ! break+ ( ,t /iff5] knees at ! weld1 :]e br\ght d[n on to ! tops ( cross-gird]s1 due to ! deflection ( ! floor1 z %[n 9 ,fig4 #aj4 ,:5 su* knees are us$1 ! angle may prop]ly be fill$ 9 ) a gusset-plate to relieve ! weld ( /ra9 & prev5t fracture4 ,illu/ration3 ,,fig4 #aj4 ,!re is "s little temptation 9 practice to make use ( ! solid web z a conv5i5t /op = balla/1 or road mat]ial4 ,special means1 p]haps at ! co/ ( "s little tr\ble1 %\ld be adopt$1 :]e necess>y1 to avoid ?is4 ,,ma9 ,,gird]s2 ,,op5 ,,webs4 ,) ^!1 z ) plate-gird]s1 defici5cy ( /r5g?--i4e4 ( section /r5g?--is seldom s m>k$ z to be a reasonable cause ( anxiety4 ,9 p>ticul> in/ances faults 9 design may result 9 /resses ( an abnormal am\nt1 ?\gh r>ely to an ext5t occasion+ any ill effects4 ,! practice ( load+ ! bottom flanges at a di/ance f ! c5tre1 ! bad effects ( :i* h already be5 dealt ) z appli$ to plate-gird]s1 is n commonly resort$ to 9 gird]s hav+ op5 webs1 nor are ^! s liable to be heap$ ) balla/ 9 imm$iate proximity to ess5tial memb]s ( ! /ructure4 ,"s defects are1 h[ev]1 occasionally se5 :i* may be rem>k$4 ,top booms ( an inv]t$ ,u section are sometimes made ) side webs too ?91 & hav+ ! l[] edges /iff5$ insuffici5tly1 or n at all4 ,:]e ?is is ! case1 ! plates may be se5 to h buckl$ out ( tru?1 %[+ t !y are unable1 z ?9 plates1 to su/a9 ! compressive /ress to :i* ! re/ ( ! boom is liable4 ,! practice ( putt+ ! great] "p ( ! boom section 9 an out] flange1 *>act]i/ic ( ?is defect1 has ! fur!r disadvantage ( ?r[+ ! c5tre ( gravity ( ! section s ne> its out] edge z to make impracticable ! be/ arrangem5t ( rivets = connection ( ! web memb]s4 ,fur!r1 s9ce all ! v>iation 9 boom section is ?r[n into ! flange-plates1 ! c5tre ( gravity ( ! section has no con/ant position along ! boom--an additional inconv5i5ce :]e correct design is aim$ at4 ,^! consid]ations indicate ! propriety ( arrang+ ! bulk1 or all1 ( ! section at ! sides1 ?us r$uc+ or gett+ rid ( ! objections nam$4 ,:]e ! bottom boom consi/s ( side plates1 only "o po9t dem&s att5tion4 ,x is f\nd t1 ?\gh nom9ally 9 t5sion1 ! end bays are liable occasionally to buckle1 z ?\gh "u compressive /ress1 & ne$ /iff5+1 n except+ gird]s :i* at "o end are m\nt$ on roll]s4 ,?is might seem to indicate t ! roll]s are ( no use2 b x is conceivable ! resi/ance arises f o!r causes1 su* z w9d =ces1 or z 9 ! case ( a bridge c>ry+ a railway1 9 :i* ! rigidity ( ! p]man5t-way may be su* t ! bridge-/ructure1 9 ext5d+ t[>ds ! roll] end1 _c move x suffici5tly1 caus+ a rev]sal ( /ress on ! light] portions ( ! bottom boom at ! knuckle end2 or by ! expos$ gird] booms becom+ v s5sibly hott] ?an ! bridge floor1 & by exp&+ at a great] rate1 cause ?is effect1 f :i* roll]s _c protect !m4 ,9 c\nt]brac+ consi/+ ( flat b>s x is desirable ei!r to secure ^! :]e !y cross o!r memb]s1 or /iff5 !m 9 "s mann] to avoid ! disagreeable *att]+ :i* w o!rwise commonly be f\nd to occur on ! passage ( ! live load4 ,occasionally diagonal ties are made up ( two flat b>s plac$ face to face1 to escape ! use ( "o v ?ick memb]4 ,:]e ?is is done1 ! two ?icknesses1 if n rivet$ toge!r along ! edges1 w be liable to op51 z ! result ( ru/+ betwe5 ! b>s 9 contact1 :5 ! evil w be aggravat$ by ! great] fre$om ) :i* moi/ure w ent] ! space4 ,o!r matt]s relat+ to op5-web gird]s w be m conv5i5tly dealt ) "u _! sep>ate head+s1 p>ticul>ly a fur!r consid]ation ( ! relation%ip subsi/+ betwe5 ! booms & floor /ructure4 ,,*apt] ,,iii4 ,,bridge ,,floors4 ,! floors ( bridges commonly give m tr\ble 9 ma9t5ance1 & _! defects are m frequ5tly ! cause :i* r5d]s recon/ruction necess>y1 ap>t f reasons n conc]n+ /r5g?1 ?an any o!r "p ( su* /ructures4 ,:5 x is consid]$ t ?is portion ( a bridge is fir/ affect$ by impact ( ! load :i* comes ^u x1 & is usually light 9 comp>ison ) ! ma9 gird]s fur!r remov$ f ! load1 & to :i* ! latt] is transf]r$ ?r\gh ! m or less ela/ic floor1 ! fact w be readily appreciat$ by ^? n already famili> ) x4 ,! end atta*m5ts ( cross & longitud9al gird]s are v liable to suff] by loos5+ ( rivets1 or1 m r>ely1 by break+ ( ! angle-irons :i* commonly make su* a connection4 ,a n unusual defect ( old "w1 :i* may also sometimes be se5 9 "w q new1 :]e ! cross-gird] dep? has f any cause be5 re/rict$1 is ! extremely cramp$ position ( ! rivets secur+ ! ends4 ,!re is small *ance ( ^! ev] be+ prop]ly tight1 if ! act ( rivet+ is r5d]$ difficult by bad design4 ,?is is ! m objectionable if x happ5s t cross-gird] ends abut aga9/ opposite sides ( ! web ( an int]m$iate ma9 gird]1 & are secur$ by ! same rivets pass+ ?r\gh4 ,at ! be/ su* rivets w n be well plac$ to insure good workman%ip1 & ! sev]e treatm5t to :i* !y become subject1 z ! cross-gird]s take _! load & deflect "u x1 w be v apt to loos5 !m4 ,! au?or has se5 a case ( ?is k9d 7see ,figs4 #aa & #ab7--r extreme1 x is true--9 :i* ne>ly ! :ole ( ! cross-gird] end rivets 7 loose1 "s ne>ly worn ?r\gh1 ?us all[+ ! cross-gird]s to be c>ri$1 n by _! atta*m5ts1 b by re/+ ^u ! ma9-gird] flanges1 :i* 9 turn1 by repeat$ twi/+1 tore ! web = a l5g? ( #d feet2 !re 0 also pron\nc$ side flexure ( ! top booms4 ,! movem5ts g5]ally on ?is bridge 7( #db-;feet span71 :e!r ( ma9 or cross-gird]s1 7 v consid]able & di/urb+4 ,x 0 remov$ aft] ab\t tw5ty-?ree ye>s' use4 ,illu/ration3 ,,fig4 #aa4 ,illu/ration3 ,,fig4 #ab4 ,!re is no necessity1 z a rule1 = ! ends ( cross-gird]s atta*$ to ! same ma9 gird] at opposite sides to be plac$ 9 l9e4 ,! au?or pref]s to arrange !m to miss1 by :i* device ea* connection is entirely sep>ate1 ! rivet+ c be m effici5tly execut$1 erection is simplifi$1 & ! rivets w be m likely to keep tight4 ,o!r special cases ( cross-gird] ends w be dealt ) "u ! head 8,rivet$ ,connections40 ,x is sometimes cont5d$ t cross-gird]s atta*$ at _! ends by a rivet$ connection %\ld be design$ z = fix$ ends1 9 :i* case !y are usually made ( ! same flange section ?r\gh\t1 ) a view to satisfy ! suppos$ requirem5ts4 ,b a gird] to be rightly consid]$ z hav+ fix$ ends mu/ be secur$ to some?+ itself unyield+4 ,) an out] ma9 gird] ( ord9>y con/ruction1 & no ov]head brac+1 ?is is s f> f be+ ! case z to leave little occasion = tak+ ! precaution nam$4 ,z ! cross-gird]s deflect1 ! ma9 gird]s w commonly yield slightly1 incl9+ bodily t[>ds ! cross-gird]s1 if ^! are atta*$ to ! l[] "p ( ! ma9 gird]s4 ,! =ce requisite to cant ! ma9 gird]s 9 ?is mann] is usually less ?an t :i* corresponds to fix+ ! cross-gird] ends1 & is1 g5]ally1 slight4 ,x is1 ( c\rse1 necess>y t ?is measure ( resi/ance at ! connection %\ld be borne 9 m9d = ! sake ( ! jo9t itself1 q ap>t f any "q ( fix+4 ,possibly1 9 q exceptional cases1 :]e v /iff ma9 gird]s are brac$ 9 su* a mann] z to prev5t cant+1 x may be prop] to consid] ! cross-gird] ends z fix$1 or = ^? ne> ! be>+s ( heavy ma9 gird]s2 b ! au?or has n met ) any example :]e cross-gird]s1 ap>t f atta*m5ts1 appe> to h suff]$ f neglect ( ?is consid]ation4 ,) cross-gird]s plac$ on ei!r side ( a ma9 gird]1 & 9 l9e1 x may also1 = new "w1 be desirable to reg>d ! ends z fix$1 & to detail !m ) ?is 9 view4 ,x does n1 h[ev]1 appe> wise to c>ry ?is assumption to its logical issue1 & r$uce ! flange section to any appreciable ext5t on ?is acc\nt4 ,! fixity ( ! ends w1 9 any su* case1 be imp]fect2 & :5 "o side only ( an int]m$iate ma9 gird] is load$1 x c h b a mod]ate effect 9 r$uc+ flange /ress at ! middle ( ! load$ floor beam4 ,illu/ration3 ,,fig4 #ac4 ,,fig4 #ad4 ,,fig4 #ae4 ,simil> reasons affect ! design ( longitud9al gird] atta*m5ts to cross-gird]s1 :i*1 if int5d$ to support rails1 _c ( necessity be s*em$ to come o!r ?an 9 l9e4 ,:]e ! floor is plat$ z "o plane surface1 !re w n usually be any tr\ble result+ if no special precautions are us$1 z ! plate itself w insure t ! longitud9als act1 9 a measure1 z cont9u\s beams1 reliev+ ! jo9ts ( abnormal /ress4 ,if ! plat+ is1 h[ev]1 design$ 9 a mann] :i* does n pres5t ?is advantage1 or if ! floor be ( timb]1 x is bett] to decide :e!r ! connections %all be consid]$ z fix$1 & made s2 or av[$ly flexible1 & detail$ 9 su* a mann] z to possess a capacity = yield+ slightly )\t injury4 ,^? connections are mo/ likely to suff] :i* are nei!r ( ! "o "* nor ! o!r1 (f]+ resi/ance )\t ! ability to ma9ta9 x4 ,figs4 #ac1 #ad1 & #ae give repres5tations ( ?ree 8spr+ jo9t0 me?ods ( insur+ yield 9 a great] or less degree4 ,= small longitud9als x is1 p]haps1 suffici5t to use end angles ) v broad flanges aga9/ ! cross-gird] web2 ^! to be rivet$ 9 ! mann] indicat$ 9 ,fig4 #ae4 ,lib]al dep? to floor beams is di/9ctly advantage\s :]e x c be secur$1 r5d]+ x easi] to design ! ends 9 a suitable mann]1 by giv+ room ne> mid-dep? ( ! atta*m5t to get 9 ! necess>y numb] ( rivets2 or :]e ! ends are rigidly atta*$ direct to v]tical memb]s ( an op5-"w truss1 ! great] dep? is effective 9 r$uc+ ! incl9ation ( ! end f ! v]tical1 ) a correspond+ly r$uc$ cant ( ! ma9 gird]s & flexure ( ! v]tical memb]1 ) small] consequ5t second>y /resses4 ,9 any case deep gird]s w contribute to /iffness ( ! floor itself1 fav\rable 9 railway bridges to ! ma9t5ance ( p]man5t-way 9 good ord]4 ,illu/ration3 ,,figs4 #af1 #ag1 #ah4 ,a po9t 9 connection ) skew-bridge floors occasionally ov]look$ is ! comb9$ effect ( ! skew1 & ma9 gird] camb]1 9 ?r[+ ! floor /ructure out ( tru?1 if no reg>d has be5 paid to ?is4 ,! result is bad cross-gird] or o!r connections2 or1 9 ! case ( be>]s runn+ ov] ! tops ( ma9 gird]s1 a necessity = special pack+s to br+ all fair 7,fig4 #ag74 ,! au?or has 9 su* cases1 :]e cross-gird]s are us$1 set ! ma9 gird] b$s at suitable levels1 9 ord] t ! cross-be>]s may all be horizontal 7see ,figs4 #af & #ah74 ,?is may n always be p]missible2 b1 h[ev] ! difficulty may be met1 x %\ld be dealt ) z "p ( ! design4 ,= small angles ( skew only may x be neglect$4 ,rivets atta*+ cross-gird] angles to ! web w occasionally loos51 probably due 9 mo/ cases to bad "w1 toge!r ) "s circum/ance ( aggravation1 z 9 ! case ( a bridge floor consi/+ ( gird]s spac$ #c feet #f in*es ap>t1 ) %ort timb] be>]s betwe51 c>ry+ rails4 ,9 _m gird]s ! top r[ ( rivets1 ( ord9>y pit* & size1 _h loos5$1 all[+ ! web1 ab\t #a_/d in* ?ick1 a movem5t ( #a_/h in* v]tically4 ,! rails be+ v close d[n ^u ! cross-gird] tops1 ?\gh n int5d$ to t\*1 _h at "s "t probably done s1 & by 8hamm]+0 produc$ ! result describ$4 ,plat$ floors are (t5 f\nd :i* are objectionable on acc\nt ( _! inability to hold wat]1 aris+ sometimes f bad "w1 z (t5 f wide spac+ ( rivets4 ,) rivets arrang$ to be easily got at1 & pit*$ n m ?an #c in*es ap>t1 a tight floor may be expect$2 b x is /ill necess>y to dra9 ! floor by a suffici5t numb] ( holes1 provid$ ) nozzles project+ bel[ ! und]side ( ! plate1 & suffici5tly long to deliv] direct into gutt]s1 :]e ^! are necess>y4 ,dra9-holes %\ld n be less frequ5t ?an "o to e #ej squ>e feet ( floor1 if flat1 & may advantage\sly be m s4 ,gutt]s %\ld slope well1 & c>e be tak5 to insure practicable jo9ts & good me?ods ( atta*m5t--a matt] too (t5 left to take c>e ( itself1 ) consid]able aft]-annoyance z a result4 ,! use ( asphalt1 or asphalt concrete1 to r5d] a plat$ floor wat]-tight is h>dly to be reli$ ^u = railway bridges1 ?\gh no d\bt effective = ^? c>ry+ roads4 ,x is extremely difficult to insure t x %all /& ! j>r+ & di/urbance to :i* x may be subject1 & "u :i* x w commonly break up1 & make matt]s worse by hold+ moi/ure1 & delay+ ! natural dry+ ( ! floor4 ,9 bulk1 z 9 tr\ghs1 x may be useful1 b 9 ?9 cov]+s on plates x _c be dep5d$ ^u4 ,floors hav+ plat$ tops are sometimes f9i%$ ov] abutm5ts or pi]s 9 a mann] :i* is n satisfactory1 ei!r z reg>ds ! c>ry+ ( loads or accessibility = pa9t+4 ,if ! plates are c>ri$ on to a dw>f wall ) ! int5tion t ! free m>g9 ( ! plate %all re/ ^u x1 !re w be a difficulty 9 secur+ ?is 9 an effici5t mann]4 ,commonly su* a wall is built up aft] ! gird] "w is 9 place1 mak+ x difficult to insure t ! wall really supports ! plate1 ! result be+ t ?is may h to c>ry itself z be/ x c4 ,9 any case1 sev]e corrosion w occur on ! und]side1 & ! plate ru/ ?r\gh mu* be=e ! re/ ( ! floor2 ! masonry also w usually be di/urb$4 ,x appe>s pref]able to =m ! end ( ! floor ) a v]tical skirt+-plate hav+ an angle or angles along ! l[] edge4 ,?is may come d[n to a dw>f wall1 b pref]ably n to t\* x1 ! skirt+ be+ design$ to act z a c>ry+ gird]4 ,a conv5i5t arrangem5t is %[n 9 ,fig4 #ai1 :i* may be us$ ei!r = a squ>e or skew bridge4 ,x w be se5 t ! plate-gird]s h no end-plates1 ! skirt+ ref]r$ to be+ c>ri$ cont9u\sly along ! floor edge1 & atta*$ to ea* gird]-web1 ! :ole ( ! m important p>ts be+ op5 to ! pa9t]4 ,illu/ration3 ,,fig4 #ai4 ,tr\gh floors consi/+ ( "o or o!r ( ! =ms ( press$ or roll$ section pres5t ! objection t x is almo/ impracticable to arrange an effici5t connection at ! ends1 if !y abut aga9/ ma9 gird]s1 & b little connection is1 z a rule1 attempt$1 & sometimes none4 ,! result is t ! load f ^! tr\ghs is deliv]$ 9 an objectionable mann]1 & ! ends be+ op5 or imp]fectly clos$1 wat] & dirt escape on to ! flange1 or o!r l$ge1 :i* supports !m4 ,a description ( press$ floor :i* promises to ov]come ?is objection1 & provide a ready means ( atta*m5t to ! webs ( plate-gird]s1 or ( booms hav+ v]tical plate-webs1 has )9 ! la/ few ye>s be5 introduc$4 ,?is has ! ends %ap$ 9 su* a mann] z to close !m & provide a flat surface ( suffici5t area = connection by rivets4 ,ea* holl[ is sep>ately dra9$ by holes ) nozzles4 ,:e!r ?is type ( tr\gh w develop faults ( its own1 due to ov]-/ra9+ ( ! metal 9 ! act ( press+1 rema9s to be se52 b z x appe>s possible to produce ! desir$ =m )\t any mat]ial ?9n+ or ?ick5+ ( ! metal1 ! cont5tion t no sev]e usage accompanies ! process appe>s to be reasonable4 ,t =m ( tr\gh+ 9 :i* ! top & bottom portions are sep>ately =m$1 & connect$ by a horizontal seam ( rivets at mid-dep?1 is f\nd 9 use ^u railway bridges to be v liable to loos5+ ( ^? rivets ne> ! ends2 less surpris+1 p]haps1 because ! slop+ sides are usually ?94 ,x is a di/9ctly difficult matt] to jo9 two or m l5g?s ( any tr\gh floor+ hav+ slop+ sides1 9 a workmanlike mann]2 ! fit ( cov]s is apt to be imp]fect1 & "s rivets1 be+ difficult ( access1 are likely to be b indiff]5tly tight1 s t if ! jo9t occurs :]e x w be m ?an lightly /ress$1 tr\ble w probably foll[4 ,a bad place = su* jo9ts is imm$iately ov] gird]s support+ ! tr\ghs1 z !re ! /ress w be mo/ sev]e1 any leakage come directly ^u ! gird]1 & rem$ial measures be m difficult to c>ry out4 ,timb] floors ( ! be/ timb]1 close jo9t$1 are m durable ?an might be suppos$4 ,! disadvantage is a difficulty 9 asc]ta9+ ! precise condition ( ! timb] aft] _m ye>s' use4 ,! au?or has se5 timb]s1 #i in*es by #i in*es1 =m+ 9 "o l5g? a close floor1 c>ri$ by ?ree gird]s1 & support+ two l9es ( way1 :i*1 :5 tak5 out1 c\ld z to a consid]able "p be kick$ to pieces ) ! foot2 :il/ 9 ano!r case1 ) ! same arrangem5t ( gird]s & close-timb]$ floor1 ! wood1 aft] be+ 9 place = ?irty-two ye>s1 01 :5 tak5 out1 f\nd to be p]fectly s\nd1 ) ! exception ( a v few bad places ( no great ext5t4 ,9 ?is in/ance1 h[ev]1 x is kn[n t ! floor--pit*-p9e--0 put 9 by a contractor :o prid$ himself ^u ! quality ( ! timb] t he us$2 ! floor be+ also cov]$ ) t> concrete1 :i* _h 9 ?is in/ance s well p]=m$ its (fice z to keep ! timb] q dry on ! top4 ,jack ar*es betwe5 gird]s make an excell5t floor = road bridges1 ?\gh heavy2 & = small bridges may be us$ to c>ry rails1 if ! gird]s are design$ to be /iff "u load4 ,! appreh5sion t brickwork or concrete w sep>ate f ! gird]-"w1 or become brok5 up "u ev5 mod]ate vibration1 does n seem to be well f\nd$1 if ! deflection is small & ! brickwork or concrete good4 ,! use ( corrugat$ %eet+ z a means ( r5d]+ ! und]side ( a bridge drop dry _c be too /rongly deprecat$4 ,if x mu/ be adopt$1 ! arrangem5t %\ld be su* z to p]mit ready removal = inspection & pa9t+4 ,x is evid5t t by box+ up ! floor /ructure1 ru/ is fav\r$1 & s]i\s defects may be develop$1 n to be discov]$ till ! %eet+ is remov$1 or some?+ happ5s4 ,illu/ration3 ,,fig4 #bj4 ,a case may be in/anc$ 9 :i* x 0 f\nd1 on tak+ d[n %eet+ ( ?is description1 t ! floor gird]s1 previ\sly hidd51 7 badly wa/$ 9 ! webs4 ,"o ( ^! gird]s _h crack$1 z %[n 9 ,fig4 #bj1 & o!rs 7 9 a condition only less bad4 ,9 any floor c>ry+ balla/ or macadam1 if means are n adopt$ to keep ! road mat]ial f ! /ructure ( ! floor1 or f ! ma9 gird]s1 corrosion may be s]i\s 9 its effects4 ,c9d] balla/ is1 p]haps1 ! wor/ 9 ?is respect1 9 its action ^u /eel or ironwork1 be+ di/9ctly m damag+ ?an any o!r k9d commonly us$4 ,rail-jo9ts ^u bridge floors are to be avoid$ :]e practicable by ! use ( rails z long z c be obta9$2 if ! bridge is small en\gh1 cross+ x 9 "o l5g?4 ,at ea* jo9t !re is likely to be hamm]+ & work+ extremely detrim5tal to floor memb]s & connections2 inde$1 x may happ5 t loose rivets w be f\nd 9 ! neighb\rhood ( su* jo9ts1 & n[h]e else on ! bridge4 ,:]e rail-jo9ts _c be avoid$1 _! position %\ld1 if !re be any *oice1 be judici\sly select$1 & ! plate-lay]s taught to close ! jo9ts & jam ! fi%-bolts4 ,illu/ration3 ,,fig4 #ba4 ,z rail-jo9ts ^u a bridge may injuri\sly affect ! floor1 s also w a weak floor be v try+ to ! rails4 ,a rem>kable in/ance ( ?is has come "u ! writ]'s notice1 :]e a bridge 7,fig4 #ba7 ( ?ree #cc-;feet spans1 hav+ out] & c5tre ma9 gird]s1 ) cross-gird]s spac$ #c feet ap>t1 re/+ ^u ! gird] flanges1 b n atta*$1 & c>ry+ two roads1 _h ! p]man5t-way 9 a v bad /ate4 ,! rails prop]1 ) supplem5t>y angle-plates1 re/$ direct ^u ! cross-gird]s1 :i* 7 decid$ly light1 & ! :ole floor _h mu* 8life0 9 x1 ! ill-effect ( :i* 0 %[n 9 ?irte5 breaks 9 ! angle-plates1 9 ea* case ne> _! ends1 g5]ally at holes4 ,x appe>s probable t sev]e /resses may be ?r[n ^u ! p>ts ( a floor1 :e!r plac$ at ! level ( ! bottom booms or ( ! top1 by *anges ( l5g? 9 ! booms due to /ress4 ,! au?or has1 un=tunately1 no direct evid5ce to (f] 9 ref]5ce to ?is1 t5d+ ei!r = or aga9/ ! cont5tion4 ,if an unplat$ floor ( cross & longitud9al gird]s ( usual arrangem5t be at ! bottom boom ( a l>ge bridge1 z ! boom l5g!ns ) ! imposition ( load ^u ! bridge1 all ! cross-gird]s f ! c5tre t[>ds ! abutm5ts w be curv$ horizontally1 ! middle portion be+ re/ra9$ by ! longitud9als f mov+ bodily ) ! ends4 ,ea* cross-gird] except t at ! c5tre1 if !re be "o1 w ?us pres5t a figure 9 plan1 concave t[>ds ! abutm5t to :i* x is ne>e/4 ,?is w be accompani$ by /ress+ ( ! connections1 & a transf] to ! longitud9als ( z mu* ( ! t5sile /ress prop]ly belong+ to ! booms z ! /iffness ( ! cross-gird]s may communicate4 ,?is 9 itself w h>dly be consid]able1 & w be ! less on acc\nt ( a slight yield+ :i* may be expect$ at ! end connections ( ea* longitud9al2 b ! effect ^u ! cross-gird]s by horizontal b5d+ w be mu* m>k$4 ,if ! case be suppos$ ( a #bjj-;feet span 9 /eel at ord9>y loads & /resses1 c>ry+ "o l9e ( way1 ) cross-gird]s #bj feet ap>t1 & hav+ no floor-plates1 x may be asc]ta9$1 neglect+ = ! mom5t any slight yield+ ( ! longitud9al gird] connections1 t ^u ! bridge tak+ its full live load !re w be ! foll[+ approximate results3 ,movem5t at ea* end ( ! end cross-gird]s ( #c_/aj in*1 equival5t to a =ce ( #g-a_/b tons1 t5d+ to b5d !m horizontally1 & a mean /ress on ! out] edges ( ! gird]s1 #ab in*es wide1 ( #h tons p] squ>e in* due to flexure1 :i*1 comp\nd$ ) ! ord9>y flange /resses1 w seem to give r al>m+ results4 ,!re w also be a longitud9al /ress 9 ! rail-gird]s1 at c5tre "p ( bridge1 ( #c_/d ton p] squ>e in*4 ,normal elongation ( ! longitud9al gird] bottom flanges1 & compression ( ! top1 modifies ! figures unfav\rably z to ! cross-gird] top flange4 ,yield+ ( ! connections nam$ be=e has be5 neglect$ 9 arriv+ at ^! /resses4 ,if !y are suffici5tly accommodat+ to give freely1 to a mean ext5t1 z betwe5 ! top & bottom ( ea* jo9t1 ( #a_/bi in*1 ^! results w disappe>4 ,x is evid5t1 h[ev]1 t we _c rely ^u good "w yield+ )\t ! exi/5ce ( consid]able =ces to cause x4 ,9 ! issue x is ju/ifiable to appreh5d t ! flex+ & /ress+ ( ! cross-gird]s w be consid]able4 ,! mo/ fav\rable case has be5 tak52 if n[ x is assum$ t ! floor has cont9u\s plat+1 ! results w\ld seem to be mu* m a/oni%+4 ,x w appe> on ?is supposition t ! boom /resses1 in/ead ( be+ tak5 :olly by ! booms1 are ab\t equally divid$ betwe5 ^! & ! floor /ructure1 ea* cross-gird] connection communicat+ its %>e ( boom /ress to ! floor1 :i* = ! end cross-gird]s w approa* #dj tons at ea* connection--consid]ably m ?an ! v]tical reaction "u normal loads4 ,palpably1 ^! conclusions mu/ be greatly modifi$ by ! yield ( longitud9al gird] ends1 & slip ( ! floor rivets 9 transv]se seams4 ,if ^! rivets be #c-a_/b in* pit* & #c_/d in* 9 diamet]1 ! /ress at ea*1 z e/imat$1 w\ld be suffici5t to induce %e> ( ab\t #f tons p] squ>e in*--m ?an en\gh to cause 8slip40 ,aft] mak+ ?is all[ance1 x is /ill evid5t !re mu/ be v s]i\s =ces at "w ab\t ! ends ( cross-gird]s "u ! conditions suppos$1 probably n less ?an "o half ! am\nts nam$1 z ) ?is r$uction ! floor rivets %\ld n yield1 giv5 reasonably good "w4 ,x is to be obs]v$ t ! effect ( live load only has be5 introduc$1 on ! presumption t ! longitud9als & floor-plat+ h n be5 rivet$ up till ! ma9 gird]s h be5 all[$ to c>ry ! major "p ( ! dead load2 b ev5 ?is _c always be conc$$4 ,! d$uction appe>s to be t ! floor & cross-gird] connections %\ld be /udi$ ) special ref]5ce to ^! possible effects1 ei!r ) ! object ( r5d]+ ! communication ( ^! =ces h>mless1 or mak+ ! floor s t x %all take little or no /ress f ! ma9 booms1 by arrang+ jo9ts across ! floor specially design$ to yield1 ! ends ( longitud9als be+ s*em$ ) ! same object4 ,:]e !re is no plat+1 ! case is1 p]haps1 suffici5tly provid$ = by mak+ ! cross-gird]s n>r[1 & ! longitud9al gird] connections flexible1 or by putt+ ^! gird]s ^u ! top ( ! cross-gird]s1 :5 /ret*+ ( ! bottom flanges ( ! rail-be>]s "u load may be expect$1 )9 a little1 to keep pace ) ! l5g!n+ ( ! ma9 booms4 ,x w\ld appe> t light press$ tr\ghs runn+ across ! longitud9als w\ld1 by yield+ 9 e section1 also furni% relief1 z comp>$ ) ! rigidity ( flat plates4 ,by plac+ ! floor at a level correspond+ to ! neutral axis ( ! ma9 gird]s1 ! communication ( /ress to ! floor may be avoid$2 b x seldom happ5s t !re is s free a *oice z to floor height relative to ! gird]s4 ,?is solution is1 !re=e1 ( limit$ application4 ,x is obvi\s t some:at simil> effects mu/ obta9 to ^? consid]$ 9 detail1 :5 ! floor /ructure lies at ! level ( top booms1 b ) =ces ( compression f ! booms to deal )1 in/ead ( t5sion4 ,,*apt] ,,iv4 ,,brac+4 ,brac+1 :e!r to /r5g!n a /ructure aga9/ w9d1 to insure ! relative positions ( its p>ts1 or = any o!r purpose1 _c be arrang$ ) too great c>e & reg>d to its possible effects4 ,=ces may be induc$ :i* ! connections w n /&1 ) loose rivets z a consequ5ce1 & ineffici5cy ( ! brac+ itself2 or1 ! connections hold+ good1 /resses 9 ! ma9 /ructure may1 p]haps1 be injuri\sly alt]$4 ,to take a n uncommon case1 let u suppose a bridge consi/+ ( f\r ma9 gird]s plac$ imm$iately "u rails ( ord9>y gauge1 & brac$ 9 v]tical planes only1 "r across f "o out] gird] to ! o!r4 ,if ! roads 7 load$ always at ! same "t1 no?+ objectionable w\ld result2 b1 z a fact1 ?is w be ! exception4 ,:5 "o pair ( gird]s only takes live load1 & deflects1 ! brac+ "u ! six-foot w endeav\r to communicate "s "p ( ?is load to ! o!r pair ( gird]s4 ,if ! brac+ is s design$ t "s correctly calculat$ portion ( ! load c be transf]r$ 9 ?is mann]1 )\t ov]-/ress+ ! b>s & rivet$ connections1 !re w be no h>mful consequ5ces2 b if n1 ! brac+s w mo/ probably "w at ! ends2 ?is1 inde$1 is :at frequ5tly happ5s4 ,!re is "o o!r effect :i* w ensue1 if ! brac+ is :olly effici5t2 a c]ta9 twi/+ movem5t ( ! bridge w occur1 :i* increases ! live load ^u ! out] gird] on ! load$ side ( ! bridge to ! ext5t ( #aj p] c5t41 ) a correspond+ lift+ =ce at ! out] gird] on ! unload$ side4 ,^! am\nts are n s]i\s1 b :olly dispose ( any advantage x is conceiv$ w be ga9$ by caus+ ! o!rwise idle gird]s to act ?r\gh ! m$ium ( ! brac+4 ,9 road bridges ( simil> arrangem5t1 ov] :i* heavy loads may pass on any "p ( ! surface1 x is cle> t ! use ( brac+ betwe5 gird]s %\ld n be tak5 z ju/ify+ ! assumption t ! load is di/ribut$ ov] _m gird]s1 & correspond+ly light sections adopt$1 unless ! effect ( twi/+ on ! :ole bridge is also consid]$1 & ju/ifies ?is view2 =1 z already /at$ 9 ! case ( ! railway bridge1 ! net result may be to increase ! gird] /resses in/ead ( r$uc+ !m4 ,g5]ally1 x may be d$uc$ t ! bett] plan = railway bridges is to brace ! gird]s 9 pairs1 leav+1 9 ! case suppos$1 no brac+ betwe5 ! two middle gird]s1 ?\gh !re w be no objection to connect+ ^! by simple transv]se memb]s ( no great /iffness1 to assi/ 9 *eck+ lat]al vibration4 ,= road bridges ( m ?an five longitud9al gird]s1 equally spac$1 x may be advantage\s to brace "r across1 ! twi/+ effect ) ?is1 or a great]1 numb] ( gird]s n1 z a rule1 lead+ to any increase ( load on any gird]4 ,figs4 #bb to #be give ! di/ribution ( live load1 plac$ z %[n1 = #c1 #d1 #e1 & #f gird]s4 ,x is to be obs]v$ t ^! /atem5ts d n apply to cases :]e !re may be also a complete sy/em ( horizontal brac+1 ! effect ( :i*1 9 conjunction ) cross diagonals1 may be greatly diff]5t1 ) consid]able =ces set up 9 ! brac+1 & a modification ( gird] /resses4 ,^! effects may be s consid]able z to call = special att5tion 9 design :]e su* an arrangem5t is adopt$4 ,illu/ration3 ,,fig4 #bb4 ,illu/ration3 ,,fig4 #bd4 ,illu/ration3 ,,fig4 #bc4 ,illu/ration3 ,,fig4 #be4 ,some:at simil> /ra9+ to t fir/ indicat$ may occur 9 brac+s plac$ betwe5 ! gird]s ( a bridge mu* on ! skew4 ,if ?is is1 on plan1 at "r angles to ! gird]s1 z is commonly & prop]ly ! case1 ! ends w evid5tly be atta*$ to ! gird]s at po9ts on _! l5g? at diff]5t di/ances f ! be>+s1 :i* po9ts1 ev5 ) bo? gird]s load$1 deflect dissimil> am\nts1 & ! brac+ w1 if at "o end atta*$ ne> a rigid be>+1 transf] "s "p ( ! load f "o gird] to ! o!r1 not)/&+ t bo? gird]s may be ( ! same span & equal extrane\s load+4 ,x w\ld n be difficult to asc]ta9 ! am\nt ( load s transf]r$ f a consid]ation ( ! relative movem5ts if free1 & ! loads on ! two gird]s necess>y to r5d] ^! movem5ts equal1 if ! deflections 7 simply v]tical2 b z !re w be "s twi/+ & yield+ ( ! gird]s on _! seats1 ! calculation becomes involv$4 ,if ! brac+ is plac$ at ab\t ! middle ( ! gird]s1 ! effects not$ w be greatly r$uc$2 fir/1 because ! diff]5ce ( movem5ts ne> ! c5tre w be less2 second1 any giv5 diff]5ce w correspond to a small] transf]5ce ( load2 &1 ?ird1 because ea* gird] w !re be m free to twi/ ?an at ! ends4 ,x !re=e appe>s t brac+s betwe5 ! gird]s ( a skew bridge %\ld n be plac$ ne> ! be>+s1 ?\gh !y may be put1 ) mu* less risk ( injury1 ne> ! middle4 ,cross-gird]s on a skew bridge are subject to =ces some:at simil> to ^? :i* may affect brac+1 r5d]+ x desirable to design _! atta*m5ts 9 a mann] :i* %all n aggravate ! matt]1 b r r$uce ! effects ( unequal v]tical displacem5t ( _! ends :]e secur$ to ! ma9 gird]s4 ,cross$ flat b>s z brac+ memb]s are objectionable on acc\nt ( _! t5d5cy to rattle1 aft] work+ loose2 b z ?is effect only ensues 9 brac+ :i* has fir/ become loose 7x be+ assum$ t ! b>s 9 any case are connect$ :]e !y cross71 ?is objection is n itself vital1 ?\gh great] rigidity is easily obta9$ by mak+ all su* memb]s ( a /iff section4 ,defective brac+ betwe5 gird]s1 f neglect ( ! v consid]able =ces x may be call$ ^u to communicate1 is v common2 ! writ] has se5 _m su* cases1 ( :i* "o is "h illu/rat$ 9 ,fig4 #bf4 ,illu/ration3 ,,fig4 #bf4 ,?is bridge1 ( ! section %[n1 & #he feet span1 _h v light web /ructure4 ,! brac+s1 ( :i* !re 7 two sets1 7 :olly ineffici5t1 ! end rivets be+ loose 9 enl>g$ holes4 ,^u ! passage ( a tra9 !re 0 a positive lur*+ ( ! gird] tops f side to side4 ,! integrity ( ! bridge 0 really dep5d5t ^u su* /iffness z !re 0 9 ! gird]s1 & unplat$ floor4 ,a common b indiff]5t me?od ( keep+ ! top memb]s ( ma9 gird]s 9 l9e is by ! use ( ov]head gird]s alone1 frequ5tly curv$ to give ! requisite cle>ance ov] ! road4 ,?is _c be consid]$ z :olly ineffici5t1 z sometimes ma9ta9$1 s9ce x is evid5t t ! clos$ frame =m$ by ! floor beams1 ! web memb]s ( ! ma9 gird]s1 & ! ov]head gird] itself1 mu/ take a great] =ce to di/ort x ?an w\ld be necess>y to cause de=mation ( a correspond+ degree1 9 an op5 frame =m$ by ! omission ( ! ov]head gird]2 b x is n a me?od to be recomm5d$1 its precise utility is difficult to e/imate1 &1 if ! cross-gird] atta*m5ts are ( a rigid "*1 t5ds to increase ! /resses induc$ at ^? connections4 ,! latt] consid]ation is1 h[ev]1 n applicable to ?is arrangem5t alone4 ,all ov]head brac+ fav\rs ?is by re/ra9+ ! t5d5cy ( ! top booms to cant inw>ds :5 ! floor beams are load$2 & ?\gh ?is re/ra9t may be q h>mless1 x is desirable t close att5tion be giv5 to ^! effects 9 design+ bridges :i* make a complete frame m or less rigid 9 its "*4 8,sway0 brac+1 sometimes introduc$ at "r angles to ! bridge betwe5 opposite v]ticals1 t5ds to emphasise ^! effects by r5d]+ ! cross-section ( ! bridge /ill /iff]1 besides mak+ x a matt] ( difficulty to asc]ta9 h[ mu* ( ! w9d =ces on ! top boom is c>ri$ to ! abutm5t by ! top sy/em ( brac+1 & h[ mu* by ! floor4 ,! au?or does n1 h[ev]1 mean to sugge/ t x _c be us$ ) propriety1 b r t extreme c>e is desirable 9 consid]+ its ultimate effect on ! re/ ( ! /ructure4 ,= gird]s ( mod]ate dep? !re may be on ^! gr\nds a di/9ct advantage 9 ab&on+ ov]head brac+1 & secur+ rigidity ( ! top boom1 & adequate resi/ance to w9d =ces1 by mak+ ! connection betwe5 ! cross-gird]s & ! web memb]s suffici5tly good to insure1 z a :ole1 a /iff ,u-%ap$ frame2 b ?is1 ) ! ord9>y type ( rock] arrangem5t "u ! ma9 gird] be>+s1 w n be entirely free f objection1 z cant+ ( ! gird]s due to floor load+ w ?r[ extreme pressure on ! inn] end ( ea* rock]4 ,!re appe>s to be no reason :y ! cyl9drical knuckle %\ld n 9 ?is case be supplant$ by a cup h+e1 all[+ angul> movem5t ( ! gird] be>+ 9 any plane4 ,illu/ration3 ,,fig4 #bg4 ,! effici5t /iff5+ ( light gird]s1 z 9 ! case ( foot-bridges1 f ! floor1 :]e ?is is at ! bottom flanges1 r5d]s v n>r[ top booms p]missible4 ,?is is a decid$ advantage :]e lightness ( appe>ance is aim$ at2 b x is n unusual to see an attempt made 9 ?is direction by introduc+ gusset plates ( v ample proportions betwe5 v]tical memb]s ( ! gird]s1 & ! project+ ends ( flimsy transoms1 c>ri$ beyond ! wid? ( ! bridge prop]1 ^! be+ ( a section :olly out ( proportion to ! brackets !y are suppos$ to secure4 ,:atev] may be ! am\nt ( /r5g? necess>y at ! po9t ,a1 9 ,fig4 #bg1 !re %\ld n be less ?r\gh\t ! transom f "o gird] to ! o!r4 ,! degree ( /r5g? & /iffness requir$ 9 ?is memb]1 & 9 ! v]tical /iff5]s is n1 z a rule1 great4 ,in=mation to enable ?is "q to be dealt ) z a matt] ( calculation is some:at scanty2 b x w\ld appe> to be suffici5t to insure safety t1 = an assum$ small am\nt ( curvature 9 ! compression memb]1 ! =ces outw>ds correspond+ to ?is curvature1 due to ?ru/1 %\ld be resi/$ by v]ticals & transoms ( /r5g? & /iffness suffici5t to re/ra9 x f any fur!r flexure4 ,x w1 ( c\rse1 be necess>y also to take c>e t ! compression memb] is good z a /rut betwe5 ! po9ts ( re/ra9t4 ,a simple & suffici5tly precise me?od ( deal+ ) ?is "q is mu* ne$$4 ,9 cases :]e ! floor weight re/s on ! flange projection1 x is also necess>y to give ! transom additional /r5g? to an ext5t enabl+ x to resi/ ! twi/+ ef=t betwe5 any two ( ^! transv]se memb]s2 fur!r1 resi/ance to w9d on ! gird] has to be provid$ 9 bo? transoms & v]ticals4 ,x may be h>dly necess>y to insi/ t brac+ int5d$ to /iff5 a /ructure aga9/ w9d1 local crippl+1 or vibration1 %\ld be made complete1 n /opp+ %ort at "s po9t1 because x _c conv5i5tly be c>ri$ fur!r1 z is sometimes done1 unless ! /r5g? ( ^? p>ts ( ! /ructure ?r\gh :i* ! =ces f ! brac+ mu/ be communicat$ to ! abutm5ts is suffici5tly great1 consid]$ ) ref]5ce to o!r /resses 9 ^? p>ts :i* h also to be endur$4 ,brac+ /opp$ %ort 9 ?is way1 mak+ only ! c5tral "p ( a bridge rigid1 may h ! effect ( increas+ ! =ces to :i* ! un/iff5$ end memb]s w\ld o!rwise be liable4 ,su* a /ructure w\ld evid5tly be mu* /iff] aga9/ w9d-gu/s ?an if no brac+ exi/$--! resi/ance to a bl[ w\ld be increas$2 b ! p[] to ma9ta9 t great] resi/ance be+ conf9$ to ! int]m$iate bays1 ! unbrac$ ends w\ld be subject to great] maximum =ces ?an if brac+ 7 :olly omitt$4 ,! net effect may /ill be bett] ?an ) no brac+1 ! po9t rais$ be+ simply t ( an increase ( /ress 9 p>ticul> end memb]s4 ,9 ! brac+ ( tall pi]s1 ! ris+ memb]s ( :i* w be subject to any consid]able /ress1 if ! diagonal memb]s are n f9ally secur$ :5 ! pi]s are "u _! full load1 or an initial /ress ( prop] am\nt induc$ 9 ^? memb]s1 ! effect ( load+ w be to r5d] !m slack2 s t an appreciable am\nt ( movem5t at ! top may occur be=e x c be limit$ by ! effici5t action ( ! brac+s4 ,?is effect "u bla/s ( w9d or cont9ual passage ( tra9s may1 inde$1 be dang]\s4 ,simil> consid]ations apply to ! top w9d brac+ ( deep gird] bridges1 influ5c+ also ! bottom brac+ 9 a contr>y mann]1 :i* calls = att5tion 9 fix+ ! unit /resses = su* memb]s4 ,! brac+ ( sea-pi]s is v liable to slack5 if made ) p9-&-eye ends1 z is (t5 done = r\nd rods4 ,! detail pres5ts advantages 9 erection1 b is n altoge!r satisfactory 9 practice4 ,su* connections are cont9ually work+4 ,9 ! f9e/ wea!r1 ) ! sea q smoo? b = an almo/ imp]ceptible wave movem5t1 ! l[] p>ts ( su* /ructures w be f\nd1 z a rule1 to h "s slight motion4 ,?is is v try+ to brac+2 nor is !re room = surprise :5 x is consid]$ t ^! oscillations1 occurr+ at ab\t t5 to ea* m9ute1 nev] :olly cease1 & am\nt 9 ! c\rse ( "o ye> to ov] five million 9 numb]4 ,brac+ atta*$ 9 su* a mann] t !re c be no initial slack1 or slack due to we> "u endless repetitions ( small am\nts ( /ress1 w h a mu* bett] *ance to keep tight4 ,! advantage pres5t$ by r\nd rods 9 (f]+ little surface to ! wat]1 is m ?an negativ$ by ineffici5cy ( ! usual atta*m5ts = su* rods4 ,! au?or has obs]v$ t brac+ ( memb]s possess+ "s /iffness1 & ) good end atta*m5ts to ample surfaces1 appe>s to /& be/ 9 ord9>y sea-pi] "w4 ,= su* /ructures ! brac+ %\ld consi/ ( a few good memb]s1 ) a solid =m ( atta*m5t1 r ?an ( a multiplicity ( light] adju/able memb]s1 :i* w commonly give great tr\ble 9 ma9t5ance2 be+ v possibly also1 9 ! case ( sea-pi] "w1 9 unskill$ h&s4 ,if r\nd rods mu/ be us$1 !y w /& mu* bett] if made ( l>ge diamet]4 ,be=e leav+ ! subject ( brac+1 x may n be out ( place to ref] to w9d pressure1 z ?is may s mu* affect ! proportion+ ( ! memb]s4 ,"s ye>s s9ce ! au?or _h occasion to exam9e a numb] ( /ructures ) respect to _! /ability4 ,( foot-bridges f #fj feet to #abj feet long1 ?ree or f\r1 :5 calculat$ on ! basis recomm5d$ by ! ,bo>d ( ,trade z to pressures ^u op5-"w /ructures1 work$ out at an ov]turn+ pressure ( f #ah lb4 to #bb lb4 p] squ>e foot4 ,^! bridges _h be5 _m ye>s 9 exi/5ce2 x is1 !re=e1 fair to assume t no su* w9d 9 ! direction requir$ = ov]turn+ _h exp5d$ its =ce ^u !m z to ! :ole surface4 ,illu/ration3 ,,fig4 #bh4 ,p>ticul>s 7 tak5 9 #ahie ( a notice-bo>d1 pres5t+ ab\t #ab squ>e feet ( surface1 :i* 0 bl[n d[n 9 ! great /orm ( ,m>* #bd ( t ye>1 at ,bil/on1 9 ,/af=d%ire4 ,x 0 situat$ at ! foot ( a slight slope1 ov] :i* ! w9d came1 /rik+ ! ob/ruction at "r angles4 ,! bo>d 0 m\nt$ on two oak po/s ( fair quality & condition1 :i* broke ne> ! gr\nd at bolt holes 7see ,fig4 #bh74 ,! =ce requir$ to d ?is1 at #ijjj lb4 modulus ( rupture--a mod]ate value--corresponds to #ej lb4 p] squ>e foot on ! surface expos$ above ! break4 ,9 ! same neighb\rhood1 at ! same "t1 consid]able damage 0 wr\ght 9 ov]turn+ *imney /acks1 to build+s & ro(s2 ! g5]al impression 9 ! locality be+ t ! /orm 0 ( exceptional1 ev5 unprec$5t$1 viol5ce4 ,bil/on1 x %\ld be not$1 lies high4 ,at ,bid/on ,hill1 ne> ,birk5head1 on ! same occasion1 a pressure ( #bg lb4 0 regi/]$4 ,9 ano!r "p ( ! c\ntry x is said to h be5 #cg lb4 ,w9d is s caprici\s 9 its effects ov] small areas z to r5d] x probable t ! maximum pressures h nev] be5 record$2 b ?is is a matt] ( little importance :]e g5]al /ability & /r5g? only are conc]n$4 ,! in/ances cit$1 ?\gh by !mselves insuffici5t to ?r[ mu* light on ! "q1 may be ( use 9 connection ) o!r kn[n examples4 ,,*apt] ,v4 ,,rivet$ ,,connections4 ,consid]able latitude is obs]vable 9 ! practice ( eng9e]s 9 ! use ( rivets4 ,numb]less exp]im5ts to det]m9e ! resi/ance ( rivet$ connections h f "t to "t be5 made1 b ^! are n to be consid]$ by !mselves z f9al1 :5 ! results ( exp]i5ce 9 actual con/ruction1 are available = fur!r enlight5m5t4 ,! class ( workman%ip s l>gely influ5ces ! degree 9 :i* rivets w ma9ta9 _! integrity t x is only by ! obs]vation ( a l>ge numb] ( cases1 includ+ all degrees ( workman%ip1 t any reliable conclusions may be drawn4 ,9 ?is respect laboratory exp]im5ts h an app>5t advantage1 z ! conditions may be kept s5sibly ! same2 b1 on ! o!r h&1 no su* inve/igation reproduces ! circum/ances ( actual use1 :i* alone mu/ 9 ! end det]m9e ! utility ( any inquiry = practical application4 ,! au?or has /udi$ ! p>ticul>s ( a numb] ( cases to asc]ta9 "u :at conditions z to /ress1 hav+ due reg>d to ! effects ( vibration1 rivets w rema9 tight1 or become loose4 ,e loose rivet t may be f\nd _c1 ( c\rse1 be tak5 z be+ due to excessive /ress2 ! m frequ5t cause is indiff]5t "w1 evid5c$ by ! fact t neighb\r+ rivets w frequ5tly be f\nd q s\nd1 ?\gh ! failure ( "s w cause a great] /ress ^u ! rema9d]4 ,:5 rivets loos5 z ! direct result ( ov]-/ress1 x is usually by compression ( ! %ank & enl>gem5t ( ! hole1 or by /ret*+ ( ! rivet & r$uction ( its diamet]4 ,in/ances ( failure by p>tial or complete %e> are extremely r>e2 inde$1 ! au?or has nev] yet f\nd "o1 ?\gh :5 a rivet has fir/ work$ loose1 z a result ( excessive be>+ pressure or bad "w1 x is n uncommon to f9d x cut or b5t z an aft] consequ5ce4 ,9 e/imat+ /resses at :i* rivets h rema9$ tight1 or loos5$1 z ! case may be1 examples h g5]ally be5 *os5 9 :i* !re c\ld be no reasonable d\bt z to ! am\nt ( ^? /resses by ! ord9>y me?ods ( computation4 ,?is is cle>ly mo/ important1 z1 if any appreciable unc]ta9ty rema9$ z to ! degree ( /ress1 ! results d$uc$ w\ld be ( little value4 ,= ?is reason ^? in/ances 9 :i* ! loads ^u gird]s1 or p>ts ( gird]s1 may f9d _! way to ! supports by m ?an "o r\te1 are to be reg>d$ ) caution1 z are ^? 9 :i* full load+ possibly nev] obta9s1 b :i* may1 on ! o!r h&1 p]haps h be5 frequ5t4 ,! work+ diamet] ( ! rivet z x fills ! hole has be5 us$ 9 mak+ ! computations2 9 "s cases f direct measurem5t f p>ticul> rivets1 9 o!rs ) a suitable all[ance = excess diamet] ( hole1 accord+ to ! class ( "w "u consid]ation4 ,deal+ fir/ ) ma9 gird]s1 x may be said t rivets atta*+ ! webs ( plate gird]s to ! flange angles r>ely loos51 ?\gh subject to consid]able /ress4 ,9 illu/ration ( ?is may be nam$ a bridge = two l9es ( way1 #he feet effective span1 hav+ two ma9 gird]s ) plate webs1 & cross-gird]s re/+ on ! top flanges1 previ\sly ref]r$ to 7see ,fig4 #bf74 ,! gird]s1 :i* 7 #f feet #i in*es deep1 _h a be>+ ^u ! abutm5ts ( #d feet2 ! rivets 7 #g_/h in* 9 diamet] & #d in*es pit*4 ,!re is 9 a case ( ?is k9d "s little unc]ta9ty z to :at is ! /ress on ! flange angle rivets at1 or v ne> to1 ! be>+s2 b1 tak+ ! v]tical r[s ( rivets at ! web jo9ts ne> ! ends z pres5t+ less unc]ta9ty1 ! /ress p] rivet works out at #dh tons1 be+ #d tons p] squ>e in* on ea* %e> surface1 & #aa tons p] squ>e in* be>+ pressure ^u ! %ank 9 ! web plate1 :i* 0 b>ely #a_/b in* ?ick4 ,?is bridge 0 frequ5tly load$ ^u bo? roads1 b ) "o road only c>ry+ live load1 ! /resses 9 ! m heavily load$ gird] w\ld be fully #ij p] c5t4 ( ^? obta9+ z a maximum4 ,!re 0 on ?is bridge1 :i* _h be5 9 use #ca ye>s1 consid]able movem5t & vibration4 ,x is by no means uncommon to f9d cases ( rivets 9 ma9 gird]s tak+ #aa tons p] squ>e in* be>+ pressure--occasionally m--& rema9+ tight4 ,z furni%+ an in/ructive1 ?\gh slightly ambigu\s1 in/ance ( rivets 9 s+le %e>1 may be cit$ a bridge n greatly less ?an t j ref]r$ to1 ( ab\t #fe feet span1 c>ry+ two l9es ( way1 !re be+ two out] & "o c5tre ma9 gird] ( multiple lattice type1 ) cross-gird]s 9 "o l5g? #d feet ap>t1 rivet$ to ! bottom booms ( ! ma9 gird]s2 ^! rivets1 by ! way1 7 9 t5sion4 ,! floor 0 plat$1 ! road consi/+ ( /\t timb] longitud9als1 *airs1 & rails 7,fig4 #bi74 ,illu/ration3 ,,fig4 #bi4 ,x %\ld be not$ t !re is 9 ?is case "s difficulty 9 asc]ta9+ ! precise behavi\r ( ! cross-gird]s1 affect+ ! proportion ( load c>ri$ by ! out] & ! inn] ma9 gird]s4 ,/rict cont9uity ( all ! cross-gird]s c\ld only obta9 if ! deflection ( ! ma9 gird]s 7 su* z to keep ! ?ree po9ts ( susp5sion ( ea* cross-gird] 9 ! same /raight l9e4 ,a close inquiry %[$ t ?is 0 v f> f be+ ! case1 & t :ile ea* cross-gird] at ! c5tre ( ! bridge w\ld1 "u load1 by relative depression ( ! middle po9t ( support1 be r$uc$ to ! condition ( two simple beams1 ^? at ! extreme ends ( ! span w\ld behave z cont9u\s gird]s4 ,) bo? roads c>ry+ eng9e loads equal to ^? com+ ^u ! bridge1 ! au?or e/imates t = ! c5tre ma9 gird] ! %e> on ! rivets ( ! end diagonals1 secur$ by "o rivet only1 0 #adi tons p] squ>e in*1 & ! be>+ pressure #afc tons2 ! flange /ress be+ #ga tons p] squ>e in* net4 ,! out] ma9 gird]s are mo/ heavily /ress$ :5 b "o road1 next to ! out] gird] consid]$1 c>ries live load4 ,= ?is condition ! /resses "w out at #i tons p] squ>e in* %e> on ! rivets ( ! end diagonals1 & #i tons be>+ pressure1 ! flange /ress be+ #eg tons p] squ>e in* on ! net section4 ,)\t int5d+ to ?r[ any d\bt ^u ! sub/antial tru? ( ^! results1 x mu/ be admitt$ t in/ances ( great] simplicity ( /ress det]m9ation are mu* to be pref]r$4 ,= purposes ( comp>ison1 b n z hav+ any o!r value1 ! results h also be5 work$ out on ! supposition ( all cross-gird]s act+ ea* z two simple beams1 & also = /rict cont9uity1 & are "h tabulat$1 toge!r ) ! conclusions giv5 above4 ,! cross-gird]s 7 mod]ately /ress$1 & ! t5sion on ! rivets atta*+ !m to ! ma9 gird]s probably did n exce$ #c tons p] squ>e in*4 ,x %\ld be po9t$ out t ! traffic ov] ! bridge 0 small4 ,! c5tre ma9 gird] b seldom bore its full load1 ?\gh at all times liable to receive x4 ,mu* importance _c1 !re=e1 be atta*$ to ! results = ?is gird]1 o!r ?an z %[+ h[ a /ructure may /& = _m ye>s1 ?\gh liable at any "t to ! developm5t ( /resses :i* w\ld commonly be reg>d$ z de/ructive1 or ne>ly s4 ,,examples ,,( ,,rivet ,,/resses1 ,,etc41 ,,9 ,,lattice ,,gird]s4 ---------------------------------------- ------------------------- ,cross- ,cross- ,gird]s ,gird]s z ,correct z ,simple ,cont9u\s ,results4 -- ,beams4 ,beams4 -------------------------------- ,/ress 9 ,tons p] ,squ>e ,in*4 ---------------------------------------- ------------------------- ,c5tre gird]1 #fc ft4 span 7bo? roads load$73 ,rivets 9 diagonals--,%e> #acg #agb #adi ,d4 ,be>+ pressure #aej #ahh #afc ,flange /ress #fh #he #ga ,out] gird]1 #ff ft4 span 7ne> road load$73 ,rivets 9 diagonals--,%e> #if #hb #ij ,d4 ,be>+ pressure #if #hb #ij ,flange /ress #ei #ea #eg ---------------------------------------- ------------------------- ,! mat]ial & workman%ip ( ! bridge 7 good4 ,! rivets ( ! c5tre gird] end diagonals1 #a in* 9 diamet]1 7 orig9ally #g_/h in*1 b on becom+ loose 7 cut out1 ! holes ream]$1 & replac$ by ! l>g] size1 :i* rema9$ tight1 & to :i* ! /ress figures apply4 ,! rivets 9 ! diagonals ne> ! c5tre1 #g_/h in* 9 diamet]1 :i* 7 subject to rev]sal ( /ress1 occasionally work$ loose1 & 7 m ?an once replac$4 ,! rivet+ 9 ! out] gird] diagonals1 subject to small] /resses1 mu* m frequ5tly develop$1 also gave tr\ble1 p>ticul>ly ^? liable to c\nt] /resses4 ,ap>t f loos5ess ( rivets1 ! g5]al appe>ance & behavi\r ( ! bridge1 :i* _h be5 9 exi/5ce ab\t tw5ty ye>s1 0 n sugge/ive ( any weakness4 ,( small] gird]s1 an example %[+ ! necessity = c>e 9 discrim9at+1 if x be possible1 betwe5 loos5ess ( rivets result+ f ov]-/ress & t due to o!r influ5ces may fir/ be quot$4 ,two tr\gh gird]s1 ( #aa feet effective span1 ea* ( ! section %[n 9 ,fig4 #cj1 #aa-a_/b in*es deep at ! ends1 #ad in*es at ! middle1 ) #a_/d-;in* webs1 & rivets #c_/d in* 9 diamet]1 ( #d-a_/b-;in* pit*1 %[$ c]ta9 defects1 ( :i* "o1 x may be incid5tally m5tion$1 0 a crack$ web 7,fig4 #ca74 ,f ! nature ( ! arrangem5t ! l[] web rivets1 :i* 7 loose1 w\ld receive ! fir/ %ock ( ! load com+ ^u ! span1 b !re 7 evid5ces indicative ( orig9al bad "w4 ,! angle b>s gap$1 sugge/+ t ^! _h fir/ be5 rivet$ to ! bottom plate1 & left suffici5tly wide to all[ ! web to be aft]w>ds ins]t$1 ! rivets fail+ to pull ! "w close1 & !n readily work+ loose4 ,"h !re is consid]able unc]ta9ty z to h[ mu* ( ! loos5+ is to be attribut$ to bad "w1 & h[ mu* to /ress4 ,x may1 h[ev]1 be rem>k$ t :atev] be>+ /ress 0 ! ultimate result ( ! load hamm]+ on ! l[] angle flanges1 loos5+ rivets nev] p]haps really tight1 ! /ress ( #g tons p] squ>e in* be>+ pressure on ! upp] rivets1 ?\gh aggravat$ by consid]able impactive =ce1 0 n suffici5t to loos5 ^!4 ,! gird]s 7 tak5 out aft] be+ 9 place sixte5 ye>s4 ,illu/ration3 ,,fig4 #cb4 ,illu/ration3 ,,fig4 #cj4 ,illu/ration3 ,,fig4 #ca4 ,an in/ance ( und\bt$ excessive be>+ pressure 0 f\nd 9 ! cross-gird]s ( a bridge1 m5tion$ on p4 #ae1 ( :i* s _m web plates 7 crack$4 ,?is bridge1 c>ry+ two l9es ( way1 _h out] ma9 gird]s1 & long cross-gird]s ) #a_/d-;in* webs & #c_/d-;in* rivets1 #d in*es pit*4 ,! rivet /resses "w out at #dc tons p] squ>e in* on ea* %e> surface1 & #bd tons p] squ>e in* be>+ pressure4 ,= "o road only be+ load$1 ! latt] figure falls to #ahe tons4 ,! traffic ov] ?is bridge1 tw5ty ye>s old1 0 consid]able1 rapid1 & heavy4 ,x is h>dly necess>y to add t a l>ge numb] ( ! rivets 7 loose1 "o ( :i* is %[n 9 ,fig4 #cb4 ,illu/ration3 ,,fig4 #cc4 ,to take ano!r case relat+ to a floor sy/em ( extremely bad design 7,fig4 #cc74 ,! ma9 gird]s 7 #aa feet ap>t1 #ce feet span1 ! floor hav+ two cross-gird]s only1 spac$ at #aa feet #c in*es1 & #i in*es deep1 support+ hog-back$ tr\gh longitud9als4 ,! cross-gird]s 7 at _! ends b #f-c_/d in*es deep1 ! di/ance f ! be>+ ( cross-gird]s to c5tre ( longitud9als c>ry+ a rail be+ #b feet #aj in*es1 9 :i* l5g? 7 eight rivets 9 ! web & angles at ! top1 & six at ! bottom1 all #c_/d in* 9 diamet]4 ,! %e> /ress on ! upp] rivets works out at #gc tons p] squ>e in* on ea* %e> surface1 ! be>+ pressure #bjf tons p] squ>e in*4 ,on ! l[] rivets ! %e> /ress becomes #ig tons1 & ! be>+ pressure #bgd tons1 p] squ>e in*4 ,c>e 0 ex]cis$ 9 comput+ ^! /resses1 t "p ( ! b5d+ mom5t c>ri$ by ! web be+ all[$ =1 b x mu/ be admitt$ t ! result is1 probably1 approximate only4 ,! sket* "h giv5 %[s ! cross-gird] end & section4 ,! rivets1 ?\gh 9 d\ble %e>1 71 z might be expect$1 loose1 not)/&+ t ! traffic ov] ! bridge 0 mod]ate1 & q sl[4 ,! floor sy/em 0 remodell$ aft] twelve ye>s' use4 ,9 illu/ration ( ! behavi\r ( rivets 9 ! ends ( long cross-gird]s1 bo? %all[ & weak1 & _m ye>s 9 use "u heavy traffic1 may be cit$ connections hav+ end angle b>s to ! cross-gird]s1 ) six rivets ?r\gh ! web ( ma9 gird]s4 ,! be>+ pressure work$ out at #gh tons p] squ>e in*4 ,_m rivets 7 loose1 b x %\ld be rem>k$ t ! workman%ip 0 n ( ! be/ class1 & ! cross gird]s flexible3 a *>act]i/ic v try+ to end rivets1 & induc+ a /ret* 9 "s1 already ref]r$ to z a possible cause ( loos5+4 ,?is w be app>5t if ! probable end slope ( weak gird]s be consid]$4 ,! au?or concludes t ?is incl9ation %\ld n1 = ord9>y cases1 exce$ #a 9 #bej2 b ! ratio mu/ l>gely dep5d ^u ! degree ( rigidity ( ! "p to :i* ! connection is made4 ,x is commonly reg>d$ z bad practice to submit rivets to t5sion1 yet ?is is frequ5tly1 ?\gh un9t5tionally1 p]mitt$ 9 end atta*m5ts1 )\t any attempt to limit ! am\nt ( t5sion4 ,) suitable re/rictions1 !re appe>s no s]i\s objection to rivet t5sion = _m situations4 ,ano!r in/ance ( cross-gird] end connections ( a diff]5t type is illu/rat$ 9 ,fig4 #cd4 ,! ma9 gird]s ( ! bridge 7 #ab feet ap>t1 ea* cross-gird] end c>ry+ its %>e ( ! half ( "o road4 ,! mean be>+ pressure ^u ! rivet %anks works out at #eh tons p] squ>e in* = ! six rivets ( ! orig9al jo9t1 b 9 ! p>ticul> jo9t %[n "s ( ! rivets _h loos5$1 mak+ ! be>+ pressure ^u ! rema9d] ab\t #hg tons p] squ>e in*4 ,x is app>5t !re mu/ h be5 consid]able /ress on ! top & bottom rivets :i* loos5$4 ,^! two rivets w\ld also1 because ( difficult access1 be 9 all likelihood insuffici5tly hamm]$ up4 ,! jo9ts work$ r badly2 ! loose rivets _h 8cut0 to a consid]able ext5t1 a process mat]ially assi/$ by ! gritty nature ( ! balla/ 7lime/one71 p>ticles ( :i*1 gett+ into ! jo9t1 contribut$ to ! saw+ action2 ?is _h cle>ly be5 tak+ effect = "s consid]able "t4 7,see ,fig4 #ce47 ,illu/ration3 ,,fig4 #cd4 ,illu/ration3 ,,fig4 #ce4 ,! two cases ( cross-gird] ends giv5 are bo? r exceptional 9 "*1 & 9 ea* case ! defects appe> to be due to g5]al bad design & workman%ip r ?an to any s]i\s excess ( be>+ pressure4 ,?is may be illu/rat$ by tak+ ! common case ( cross-gird]s1 #b feet deep1 c>ry+ two roads1 & hav+ end angle irons rivet$ to ! web & /iff5]s ( ! ma9 gird]s by t5 rivets 9 s+le %e> at ea* end4 ,9 ?is example1 :i* is1 = old "w1 simply typical1 & does n relate to any specific in/ance1 ! be>+ pressure on ! rivets w "w out at f #f to #h tons p] squ>e in*1 & w seldom be accompani$ by loos5ess ( rivets1 & !n only z a result ( faulty "w4 ,"s sket*es ( rivets tak5 f old bridges h already be5 giv5 9 connection ) ! cases to :i* !y belong2 a few o!rs are "h %[n 7,figs4 #cf to #dj7 to fur!r illu/rate :at may be ! actual condition ( rivets aft] "s ye>s' use1 & h[ diff]5t f ! ideal rivet ^u :i* calculations are bas$4 ,^! are1 h[ev]1 bad in/ances4 ,illu/ration3 ,,fig4 #cf4 ,illu/ration3 ,,fig4 #cg4 ,illu/ration3 ,,fig4 #ch4 ,illu/ration3 ,,fig4 #ci4 ,illu/ration3 ,,fig4 #dj4 ,x %\ld be notic$ t rivets may1 if 9 d\ble %e>1 be loose 9 ! middle ?ickness1 due to enl>gem5t ( ! hole 9 ! c5tral "p & compression ( ! rivet1 & yet %[ no sign ( ?is by te/+ ) ! hamm]4 ,!re is1 h[ev]1 g5]ally m>k$ evid5ce ( ano!r k9d 9 ! 8work+0 ( ! inn] "p1 z1 = in/ance1 ! web ( a plate gird]1 9 :i* case a discoloration due to ru/ is to be f\nd along ! edges ( ! angle b>s1 or a movem5t may be detect$ on ! passage ( live load4 ,r$ ru/ is1 9 fact1 frequ5tly an indication ( some?+ wrong1 :5 no o!r evid5ce is app>5t4 ,9 plate gird]s hav+ ,t or ,l b>s br\ght d[n & crank$ on to ! top ( %all[ cross-gird]s1 x is n uncommon to f9d ! rivets atta*+ ^! b>s to ! cross-gird] tops loose1 due to causes already dealt )4 ,! rivet$ connection %\ld1 z to /r5g?1 be> "s relation to ! /r5g? & /iffness ( ! p>ts secur$1 if ! rivets are to rema9 s\nd4 ,x may be well to give "h a summ>is$ /atem5t ( ! results already nam$1 = purposes ( ready ref]5ce4 ,^! by !mselves are n suffici5t to enable work+ /resses to be d$uc$1 ?\gh !y are in/ructive4 ,! au?or has f\nd _m in/ances ( %e> & be>+ /resses 9 excess ( ^? usually sanction$1 "u :i* ! rivets behav$ well1 b is n n[ able to give precise p>ticul>s ( ^!4 ,,examples ,,( ,,rivet ,,/resses4 ---------------------------------------- -------------------- -- ,span ,:]e ,%e> ,s+le,be>+ ,tight or ,loose4 9 ,f\nd4 ,/ress or ,pressure ,feet4 9 ,d\ble9 ,tons ,tons ,%e>4 p] p] ,squ>e ,squ>e ,in*4 ,in*4 ---------------------------------------- -------------------- ,ma9 #he ,web #dj ,d #aaj ,tight4 gird]s #ff ,diagonals #ij ,s #ij ,_m loose4 #fc #adi ,s #afc ,tight g5]ally4 #aa ,web #ad ,d #gj ,tight4 ,small #bf #dc ,d #bdj ,_m loose4 gird]s #aa #gc ,d #bjf ,loose4 #aa #ig ,d #bgd ,loose4 ,end #bg ,ends #ed ,s #gh ,loose4 connec- #ab #ah ,d #eh ,_m loose4 tions #hg 7,type case7 #bf #dh ,s #gj ,tight4 ---------------------------------------- -------------------- ,x is probable t ! fact ( a rivet be+ 9 s+le or 9 d\ble %e> l>gely affects its ability to resi/ ! effects ( be>+ pressure1 z commonly e/imat$4 ,9 ! fir/ case1 ! rivet-%ank mu/ be> heavily on ! half-?ickness ( ! plates or b>s ?r\gh :i* x passes1 r ?an on ! :ole ?ickness2 & x is to be suppos$ t "u ?is condition x w "w loose at a l[] av]age /ress ?an if x 7 9 d\ble %e>1 & ! pressure bett] di/ribut$4 ,illu/ration3 ,,fig4 #da4 ,illu/ration3 ,,fig4 #db4 ,! au?or has no v def9ite in=mation 9 support ( ?is cont5tion1 b sugge/s t = d\ble %e> ! p]missible be>+ pressure may probably be z mu* z #ej p] c5t4 great] ?an = rivets 9 s+le %e>2 ! diff]5ce be+ made r 9 ! direction ( increas+ ! all[able load on d\ble-%e> rivets1 ?an 9 r$uc+ t ^u rivets 9 s+le %e>4 ,! propriety ( ?is is evid5t :5 x is consid]$ t ! practice has commonly be5 to make no di/9ction1 s t :atev] be>+ pressures are f\nd to be suffici5t = bo? cases may be increas$ = ^? capable ( tak+ ! great] am\nt4 ,figs4 #da & #db1 "h giv51 illu/rate ! behavi\r ( rivets "u ! two conditions4 ,) ref]5ce to ! am\nts ( ! /resses to :i* rivets may be subject1 ! au?or concludes1 z a result ( 8 exp]i5ce1 c\pl$ ) a consid]ation ( kn[n laboratory te/s1 t = all dead load ^! may be q prud5tly high] ?an is frequ5tly tak54 ,= iron ! %e> /ress to be #aj p] c5t4 less ?an ! /ress ( p>ts jo9$2 & ! be>+ pressure--= s+le-%e> rivets1 #bj p] c5t42 & = d\ble-%e> rivets1 #hj p] c5t4 great]4 ,= ord9>y mild /eel ! %e> /ress to be #bj p] c5t4 less ?an ! /ress 9 p>ts connect$1 & ! be>+ pressure equal to x = s+le-%e> rivets2 & #ej p] c5t4 m = rivets 9 d\ble %e>1 ?\gh ! two latt] values may probably approa* ^? = wr\ght iron 9 /eel ( ! high] grades sometimes us$ 9 bridge-"w4 ,= live load1 or "p live & "p dead load1 ! same rules may apply1 ! r$uction ( ! nom9al work+ /ress1 arriv$ at by any "o ( ! me?ods 9 use :i* may be adopt$1 affect+ bo? ! p>ts connect$1 & ! rivets connect+ !m4 ,= rev]se /resses x is advisable to keep ! %e> /ress 9 any rivet s l[1 say #c tons p] squ>e in*1 t ! frictional resi/ance ( ! p>ts gripp$ by ! rivets %all be suffici5t to prev5t any t5d5cy to slip "u ! influ5ce ( ! small] ( ! two =ces to :i* ! "p is liable1 to insure t1 if br\ght to a be>+ 9 "o direction by ! great] =ce1 x %all n g back ) rev]sal ( /ress4 ,?is requirem5t may be op5 to "s "q ) respect to good ma*9e-rivet$ "w1 b = h&-rivet$ connections x may c]ta9ly be adopt$ ) wisdom4 ,! foll[+ table w %[ at a glance h[ ! /resses propos$ v>y ) ! unit /resses gov]n+ ! ma9 sections4 ,,propos$ ,,table ,,( ,,rivet ,,/resses4 ---------------------------------------- ---------------- ,unit ,/ress ,be>+ ,pressure,be>+ ,pressure 9 ,%e> ,/ress4= ,s+le-,%e>= ,d\ble-,%e> ,memb]4 ,rivets4 ,rivets4 ---------------------------------------- ---------------- ,wr\ght ,iron4--,tons p] ,squ>e ,in*4 #cj #bg #cf #ed #dj #cf #dh #gb #ej #de #fj #ij #fj #ed #gb #ajh #gj #fc #hd #abf ,/eel4--,tons p] ,squ>e ,in*4 #dj #cb #dj #fj #ej #dj #ej #ge #fj #dh #fj #ij #gj #ef #gj #aje #hj #fd #hj #abj #ij #gb #ij #ace ---------------------------------------- ---------------- ,,note4--,t5sion on rivets to be limit$ to "o-half ! p]missible %e> /ress1 ! holes be+ slightly c\nt]sunk "u snap-head4 ,x may be object$ t ! %e> /resses 9 ! propos$ table are some:at high = wr\ght iron & /eel4 ,?is feature is int5tional1 & is support$ by ! consid]ation t :]eas !re may be loss ( /r5g? 9 ! memb]s ( a /ructure by wa/e1 !re is no su* loss 9 rivets1 if ! "w is s design$ t !re %all be no loos5+4 ,any all[ance t may be desirable = loose or defective field rivets is left to be dealt ) z may be consid]$ advisable = ea* p>ticul> case1 ! table z x /&s be+ applicable only to rivet+ n bel[ ! /&>d ( fir/-rate h& "w4 ,cases ( loose rivets 9 ma9 gird]s ov] #ej feet span1 due to any cause b bad "w1 are extremely r>e1 unless result+ f ! action ( "s o!r "p ( ! /ructure4 ,x may be /at$ broadly t = railway bridges ( less ?an p]fect design1 ! ne>] ! rail1 ! m loose rivets1 g5]ally at connections4 ,?is is1 no d\bt1 l>gely due to ! sev]e impact ( ! load1 ! effects ( :i* are great] ne> ! rail1 bo? because ( ! small proportion ( dead load1 & because ?is effect has be5 b little modifi$ by ! ela/icity ( any consid]able l5g? ( int]v5+ gird]-"w4 ,9 addition to ?is1 x is q usual to f9d ! rivets m heavily /ress$1 ev5 ?\gh ! load be consid]$ z 8/atic10 9 ! floor sy/em ?an 9 ! ma9-gird]s1 ?\gh ! rev]se %\ld be ! case4 ,x is un=tunate t ^? p>ts :i* require ! be/ rivet+--viz41 ! connections--are commonly dealt ) by h&2 & = ?is reason x is ! m necess>y to design ^! ) ! greate/ c>e4 ,any arrangem5t :i* fav\rs ! gradual acceptance ( /ress by "o "p f ano!r w contribute to ! integrity ( rivet$ connections1 & less5 ! liability ( ! mat]ial to develop faults4 ,9 o!r bran*es ( design ?is is well recognis$1 b appe>s 9 mu* old bridge "w to h be5 entirely ov]look$4 ,bridges c>ry+ public roads v seldom furni% examples ( loose rivets2 ! conditions are g5]ally mu* m fav\rable1 impact be+ practically abs5t1 full load+ infrequ5t1 & ! proportion ( dead load to live1 high4 ,x is1 p]haps1 h>dly necess>y to insi/ ^u rivets be+1 ap>t f m]e consid]ations ( /r5g?1 suffici5tly ne> toge!r to insure close "w & exclude moi/ure4 ,outside edge seams %\ld nev] be m widely spac$ ?an #af times ! ?ickness ( ! plates2 #ab ?icknesses ap>t is bett]4 ,9 ! case ( angle1 tee1 & *annel sections1 ! great] /iffness ( ! section makes wid] spac+ all[able up to1 say1 #bj times ! ?ickness2 b ?is mu/ be gov]n$ l>gely by ! am\nt ( rivet+ requir$ to pull ! p>ts close toge!r4 ,:]e m ?an f\r ?icknesses are to be gripp$ by ! rivets1 #c_/d in* 9 diamet] is h>dly suffici5t to insure tight "w1 & q unsuitable if ! plates exce$ #e_/h in* ?ick4 ,,*apt] ,,vi4 ,,high ,,/ress4 ,high /ress1 provid$ x be well bel[ t at :i* imm$iate injury results1 or possible failure1 is n uni=mly objectionable4 ,x may be fir/ consid]$ relative to ! absolute & ela/ic limits ( /r5g?1 next ) respect to ! range ( /ress1 &1 f9ally1 ) reg>d to ! frequ5cy ( application4 ,= practical purposes--t is1 = ! cont9u$ effici5cy ( a /ructure--! limit ( ela/icity mu/ be consid]$ to be ! limit ( /r5g?1 or1 m /rictly1 ! limit = all ^? p>ts ( ! /ructure :i* mu/1 s long z x la/s1 be liable to ! orig9al measure ( /ress4 ,!re may be places 9 a bridge1 h[ev]1 ov]-/ress$ only 9 ! e>li] p]iod ( its exi/5ce1 :i*1 by be+ ov]-/ress$ & suff]+ de=mation1 p]mit ! orig9 ( ?is di/ortion to be h>mlessly met 9 "s o!r way4 ,9 su* a case ! injury done to t "p does n1 ( necessity1 lead to any culm9at+ disa/]2 inde$1 7 x n = ?is pla/icity x is probable a l>ge numb] ( bridges w\ld fail aft] be+ 9 use b a %ort "t4 ,z = rivet+1 s 9 deal+ ) ! am\nt ( /ress to :i* a memb] is suppos$ to be liable1 x %\ld be cle>ly und]/ood by :at me?od ?is has be5 arriv$ at1 :e!r ! value assign$ is ! actual measure ( ! /ress1 or simply ! conv5tional am\nt arriv$ at 9 ! conv5tional way2 p]haps neglect+ web section 9 plate gird]s1 or )\t reg>d to ! v>i\s influ5ces :i* may r$uce or increase ! nom9al am\nt ( /ress1 or includ+ only a p>tial recognition ( ^? influ5ces4 ,9 any case quot$ ! /ress nam$ is t at :i* ! au?or arrives by ! ord9>y me?ods ( computation c>efully appli$1 :]e ^! appe> to be suffici5tly precise1 unless any qualify+ rem>k be add$4 ,extreme flange /ress is 9 special cases comput$1 fir/ on ! gross section by e/imat+ ! mom5t ( in]tia on t basis1 & d$uc+ ! /ress at ! holes f ! ratio ( net to gross section at ! extreme fibres2 a me?od m correct ?an by ref]5ce to ! mom5t ( in]tia ( ! net section4 ,any exhau/ive ref9em5t 9 ! /udy ( /resses is n attempt$1 bo? because x is beyond ! au?or's p[]s ( analysis1 & = ! reason t su* results are n comp>able ) ! results ( ord9>y me?ods ( calculation 9 practice4 ,effective spans are tak5 at mod]ate values1 & all exagg]ation is avoid$4 ,! effects ( impact 9 any "p v>y s mu* ) ne>ness to1 or remot5ess f1 ! liv+ load1 & ! frequ5cy ( developm5t ( ! maximum /ress f all causes act+ toge!r is s mu* affect$ by ! same consid]ation1 t x is app>5t a nom9al /ress :i* may be h>mless 9 "o "p ( a bridge may be de/ructive 9 "s o!r1 a /atem5t borne out by obs]vation4 ,/ress1 z ord9>ily /at$--i4e41 at s mu* p] squ>e in*1 uni=m across a section--is seldom a cause ( tr\ble4 ,9 ne>ly all cases ( failure !re is an accompany+ localis$ de/ructive /ress1 ei!r 9 rivets or else:]e1 ) crippl+ or de=mation ( "s ess5tial "p4 ,9 ! t5sion flanges ( ma9 gird]s ) uncomplicat$ /ress1 ?is may run up to an am\nt v consid]ably beyond ! ord9>y limits )\t produc+ signs ( di/ress4 ,! same rem>k applies to ! compression flanges1 if ^! be 9 !mselves suffici5tly /iff1 or prop]ly re/ra9$ f side flexure4 ,9 support ( ! above /atem5t may be quot$ ! foll[+ in/ances relat+ to wr\ght-iron /ructures3-- ,a bridge ( #fj feet effective span1 hav+ gird]s imm$iately "u ! rails1 _h a flange /ress ( #fc tons p] squ>e in*4 ,ano!r ( #fd feet span1 c>ry+ two l9es ( way1 ) outside ma9 gird]s & cross-gird]s1 _h ! flanges ( ! =m] /ress$ to #fh tons p] squ>e in*4 ,a ?ird1 ( #gf feet span1 ( simil> con/ruction to ! la/1 0 /ress$ 9 ! ma9 gird] flanges to #ge tons p] squ>e in*4 ,! webs 7 n includ$ 9 ! computation2 ! figures1 !re=e1 comp>e ) ord9>y practice4 ,9 ^! ?ree cases ! ma9 gird]s %[$ no signs ( di/ress1 ref]able to ! results /at$1 ?\gh ! top flanges 9 ! la/ case 7 curv$ inw>ds4 ,! effect ( ?is flex+ ( ! flange w\ld be1 ( c\rse1 to increase ! am\nt ( compressive /ress along "o edge1 ?\gh to :at degree _c n[ be /at$4 ,illu/ration3 ,,fig4 #dc4 ,illu/ration3 ,,fig4 #de4 ,illu/ration3 ,,fig4 #dd4 ,a fur!r in/ance ( consid]able flange /ress occurr$ 9 a bridge ( sev5 ne>ly equal cont9u\s spans1 #be feet g5]ally1 ! end & greate/ span be+ #bi feet #f in*es1 c5tre to c5tre ( be>+s4 ,"s details ( ! bridge are giv5 9 ,figs4 #dc to #de4 ,! f\r inn] ma9 gird]s "u rails 7 #b feet deep1 ) webs #a_/b in* ?ick ov] pi]s1 & #c_/h in* at abutm5ts1 hav+ flanges ( two ,l b>s1 #c in*es by #c in*es by #e_/h in*4 ,!re 7 also two out] gird]s ( ! same dep?1 ) s+le ,l b>s4 ,plate diaphragms ( full gird] dep? & p>ticul>ly /iff 7 c>ri$ "r across ! bridge at ! c5tre ( ! spans1 & ov] ! pi]s4 ,! gird]s1 ?\gh evid5tly design$ to be cont9u\s1 _h v poor flange jo9ts at ea* be>+1 ( little m ?an "o half ! flange /r5g? 7see ,fig4 #de74 ,x is d\btful if ! gird]s act$ ) /rict cont9uity = long aft] erection1 z ! excessive /ress 9 ! rivets ( ! flange jo9t w\ld1 = t condition1 h be5 ne>ly suffici5t to %e> !m4 ,x is probable t ?is be+ s1 ! jo9ts fir/ yield$1 reliev+ ! b5d+ mom5t ov] ! pi]s1 & increas+ x ne> mid-span4 ,:e!r ! end spans be consid]$ z /rictly cont9u\s ) ! re/1 or z simple beams1 ! maximum b5d+ mom5ts w\ld n greatly diff]1 ?\gh occurr+ = cont9uity ov] ! pi]1 = free beams at ! c5tre4 ,!re is1 h[ev]1 an int]m$iate condition :i* makes ! mom5ts at ^! two places less ?an ei!r maximum1 b equal to ea* o!r2 a condition ( semi-cont9uity agreeable to a p>tial effici5cy ( ! jo9ts ref]r$ to4 ,x is ?is /ate :i* has be5 calculat$1 giv+ ! m9imum /ress value t c be accept$4 ,! diaphragm has be5 assum$ to transf] to ! out] gird]s a due proportion ( ! load4 ,) ?is explanation x may n[ be /at$ t1 "u eng9e loads correspond+ to ^? runn+1 ! flange /ress work$ out at #gd tons p] squ>e in* t5sion1 web includ$1 or #ig tons p] squ>e in* )\t consid]+ ! web2 :i* /resses1 x is m ?an probable1 may h be5 great]4 ,! figures include ! consid]ation ( any?+ :i* may contribute to l[]+ ! /ress1 & are h>dly to be comp>$ ) ^? work$ to 9 ord9>y design ( new "w1 9 :i* x w\ld be q usual to neglect ! assi/ance ( ! out] gird]s & ! webs1 to "w to heavie/ eng9e-loads1 & possibly include an all[ance = ! effects ( settlem5t4 ,dealt ) 9 ?is way ! gird]s w\ld seem to be ( ab\t "o-f\r? ! /r5g? t w\ld be requir$ 9 ! design ( a new bridge1 9 :i* c]ta9 elem5ts ( /r5g? w\ld be delib]ately ignor$4 ,! ironwork 0 9 good condition1 !re 0 no ord9>y evid5ce ( weakness ap>t f ! calculat$ results1 ! vibration 0 di/9ctly mod]ate1 & ! deflection1 ?\gh n record$1 0 c]ta9ly small4 ,! bridge did1 inde$1 seem some:at in]t "u load1 & fav\rs a suspicion1 ! au?or ent]ta9s1 t old gird]work long ov]/ress$ may h a s5sibly high] modulus ( ela/icity ?an new] "w at m mod]ate /resses4 ,! traffic 0 n v consid]able1 & bo? roads1 ( ! same spans1 b seldom load$ at ! same "t2 ?\gh ) ?is con/ruction ( bridge !re w\ld 9 ei!r case be v little diff]5ce4 ,! au?or recalls no reason = suppos+ t ! pi]s _h yield$ 9 any s5sible degree4 ,! bridge 0 rebuilt aft] "s ?irty-six ye>s' use4 ,/ress ( consid]able am\nt 9 ! flanges ( a lattic$ ma9 gird] ( #fc feet span has already be5 notic$ 9 ! *apt] on 8,rivet$ ,connections10 :i* = ! t5sion boom work$ out to #ga tons p] squ>e in*1 ! flanges 9 ?is case %[+ no signs ( weakness4 ,an in/ance has also be5 giv5 9 deal+ ) a case ( side flexure 9 :i* ! extreme fibre /ress 0 calculat$ to be #aj tons p] squ>e in*1 ! gird] recov]+ its =m :5 reliev$ ( load4 ,z to /ress 9 cross-gird] flanges1 an example may be quot$ ( a bridge ( #aji feet span1 c>ry+ two roads1 hav+ outside ma9 gird]s1 ) cross-gird]s betwe52 ^! latt] 7 /ress$ 9 ! flanges to #fg tons p] squ>e in* 7webs n includ$71 if ! p>tial di/ribution among ! gird]s 7:i* 7 spac$ #f feet ap>t7 by ! rails & longitud9al timb]s be neglect$4 ,!re is "s reason to ?9k 9 ?is in/ance t di/ribution _h ! effect ( r$uc+ ! /ress quot$1 z ! obs]v$ deflection ( ! cross-gird]s 0 mat]ially less ?an t calculat$ = gird]s act+ indep5d5tly ( ea* o!r1 ?\gh ?is may be 9 "p due to a cause already h9t$ at4 ,rigidity ( ! cross-gird] ends1 :]e atta*$ to ! heavy ma9 gird]s1 w\ld also t5d to mod]ate ! /ress4 ,no v def9ite conclusion c !re=e be d$uc$ f ?is in/ance4 ,to take ano!r case ( less unc]ta9ty1 ! bridge ( #ce feet span 7see ,fig4 #cc71 ref]r$ to 9 8,rivet$ ,connections10 may aga9 be cit$4 ,! extreme fibre /ress 9 ! cross-gird] flanges work$ out at #fc tons p] squ>e in*1 web includ$1 or #fe tons1 exclusive ( ! web4 ,x _c be said 9 ?is example t ! gird]s %[$ no signs ( weakness1 z ! deflection "u live load 0 #a_/b in* on ! span ( #aa feet1 9 addition to a p]man5t set ( #c_/d in*1 l>gely due1 h[ev]1 to 8work+0 rivets4 ,a bett] & altoge!r conclusive case ( ! way 9 :i* cross-gird]s may occasionally suff] consid]able /ress1 & %[ no sign1 is furni%$ by two cross-gird]s1 ( :i* "s p>ticul>s are "h giv54 ,^! gird]s occurr$ 9 ! floor ( a v acute angl$ skew bridge1 rivet$ at "o end to ! ma9 gird]s 9 a mann] :i* 0 v f> f fix+ ! ends1 re/+ at ! o!r end on a masonry abutm5t4 ,! fir/ gird] 0 ab\t #ai feet effective span1 #ab in*es deep 9 ! web1 ) angle b> & plate flanges4 ,! gird]s 7 spac$ #f feet ap>t1 & 7 connect$ "u ! rails by ,t-b>s1 crank$ d[n to face ! webs1 & rivet$ ?r\gh4 ,?\gh ^! ,t's _h little /iffness1 yet ! frequ5t v]tical movem5ts ( ! gird]s relative to ea* o!r1 "u pass+ loads1 _h brok5 ! majority ( ! ,t-b>s at ! b5ds1 s t no notice ne$ be tak5 ( ^! z transf]r+ load f any "o cross-gird] to its neighb\r4 ,! floor cov]+ consi/$ ( timb]s ab\t #d in*es ?ick1 also incompet5t to transf] any s5sible proportion ( ! load on a gird] to o!rs #f feet di/ant4 ,^u ! floor 0 c9d] balla/1 ) sleep]s1 *airs1 & ord9>y bull-head$ rails4 ,! /ress to :i* ! gird] 0 liable works out at #hd tons p] squ>e in*1 on ! extreme fibres ( ! net section1 web includ$2 or #ia tons1 neglect+ ! web1 "u eng9e-loads ( a common am\nt4 ,! o!r gird] _h an effective span ( ab\t #bb feet1 z be=e #ab in*es deep 9 ! web1 ) angle b> & plate flanges4 ,! /ress p] squ>e in* 0 #aje tons1 web includ$1 or #aaa tons p] squ>e in*1 neglect+ ! web4 ,?is gird] c>ri$ ?ree rails1 "o ( :i* 0 ne> to ! abutm5t be>+1 s t !re 0 no great diff]5ce 9 ! /ress induc$ :e!r all ?ree rails 7 load$ or ! pair only4 ,! traffic ov] ! bridge 0 v great1 b ( mod]ate spe$4 ,x mu/ h be5 a common occurr5ce = ! gird]s to take ! full loads4 ,! heavi] eng9es pass$ scores ( times 9 a day--light] eng9es probably "o hundr$ times4 ,! bridge 0 ab\t tw5ty ye>s old1 yet ^! cross-gird]s1 :5 remov$1 %[$ no o!r sign ( age & we> ?an t due to ru/4 ,illu/ration3 ,,fig4 #df4 ,all ! =ego+ in/ances relate to wr\ght-iron bridges4 ,two cases ( /eel con/ruction are "h add$1 ! fir/ ( ^! furni%+ an example ( high gird] /ress some:at rem>kable4 ,?is 0 f\nd 9 a tr\gh gird] ( a /range patt]n1 ( :i* a section is "h giv5 7,fig4 #df74 ,! bridge to :i* x belong$ c>ri$ a sid+1 ov] :i* eng9es ( less ?an ! heavie/ class sometimes pass$ at a crawl+ pace4 ,! l>g] ( ! two gird]s c>ry+ ! rails 0 #ae feet #h in*es effective span4 ,! sides ( ! tr\gh consi/$ ea* ( two v]tical plates1 orig9ally #a_/b in* ?ick1 b wa/$ to an aggregate ?ickness ( #e_/h in*4 ,^! plates #f in*es deep1 7 connect$ at _! l[] edges to angle b>s1 #c in*es by #c in*es by #a_/b in*1 :i* aga9 7 rivet$ to a bottom plate #af in*es wide1 orig9ally #a_/b in* ?ick1 wa/$ to #c_/h in*4 ,ly+ 9 ! bottom ( ! tr\gh1 & rivet$ ?r\gh ! inn] angle flanges1 0 a bridge-rail4 ,assum+ t ! metal reta9$ its ela/ic prop]ties f top to bottom ( ! section1 at :atev] /ress1 ?is works out at #cb tons p] squ>e in* at ! extreme top fibre1 & #ae tons at ! bottom1 on ! net section4 ,z puddl$ /eel1 ( :i* ! gird]s 7 made1 may h a t5acity ( #de to #ee tons p] squ>e in*1 ! assumption is probably correct4 ,! au?or has no record ( ! deflection1 b x may be rem>k$ x 0 su* t to /& "u ! gird]1 ) a tank eng9e pass+ ov]1 requir$ "s det]m9ation4 ,a po9t ( additional int]e/ 9 ?is little bridge is t1 ?\gh made ( /eel1 x dates z f> back z #ahfa1 hav+ be5 9 use ?irty-two ye>s :5 remov$4 ,! p>ticul> v>iety ( /eel us$ 0 kn[n z ,fir?'s puddl$4 ,! evid5ce ( ?is consi/s 9 correspond5ce %[+ t p]mission _h be5 ask$ ( ! controll+ au?ority1 by ! only us]s ( ! sid+1 to apply ?is mat]ial1 ) no evid5ce ( any refusal4 ,at ab\t ! same "t ?is /eel 0 also us$ ^u ! railway conc]n$ 9 ! top flanges ( "s gird]s ( consid]able span4 ,! appe>ance ( ! tr\gh gird]s to :i* ! =ego+ p>ticul>s apply 0 di/9ctly diff]5t to t :i* might be expect$ 9 ord9>y wr\ght iron4 ,! top edges ( ! v]tical plates 7 wa/$ away1 smoo?1 & r\nd$ 9 a mann] /rongly sugge/ive ( a /eely "*4 ,f9ally1 ! way 9 :i* ! gird]s held up to _! "w = s long is1 by itself1 conclusive on ! po9t4 ,! bridge-rail appe>$ to be ( wr\ght iron1 ! diff]5t modulus ( ela/icity ( :i* has be5 includ$ 9 ! calculation ^u :i* ! prec$+ results are bas$4 ,t ^! gird]s /ood s well is1 p]haps1 l>gely due to ! fact t ! load c>ri$ by !m 01 ?\gh v>y+ )9 wide limits1 practically free f impact1 :i*1 _h ! load pass$ ov] quickly1 w\ld1 ) gird]s s small1 %all[ & flexible1 h be5 v s5sible4 ,! second in/ance ( /eel con/ruction 9 :i* some:at high /ress is manife/ is t ( "s /eel tr\gh+ ( ! ,l9dsay patt]n1 us$ 9 a bridge built 9 #ahhe4 ,! tr\ghs ran p>allel to ! rails1 hav+ an effective span ( #ah feet #h in*es4 ,! dep? ( ! section 7:i* is %[n 9 ,fig4 #dg71 0 #h-a_/b in*es1 mak+ a ratio ( dep? to span ( #a_/bh4 ,! road 0 ( balla/1 sleep]s1 *airs1 & #he-lb4 rails4 ,illu/ration3 ,,fig4 #dg4 ,assum+ ?is to be c>ri$ on six tr\ghs1 :i* corresponds to #aa feet #c in*es ( wid?1 ! extreme fibre /ress works out at #ge tons p] squ>e in*1 "u usual eng9e-loads4 ,! bridge :5 exam9$ aft] f\rte5 ye>s' use 0 9 good condition1 & at t "t b little ru/$2 b ! end seam rivets 71 z is n uncommon ) su* tr\gh+1 loose4 ,! traffic ov] ! bridge 0 consid]able1 b n at great spe$4 ,on ! opposite page are set out ! results :i* h be5 giv51 9 tabulat$ =m1 z 0 done = rivet /resses1 to enable ready comp>ison to be made4 ,,examples ,,( ,,high ,,/ress4 ---------------------------------------- ---------------------- ,span ,"p ,/ress p] ,t5sion ,condition4 9 ,/ress$4 ,squ>e ,in*4 or ,feet4 --------------,compres- -- ,webs ,webs sion4 ,9- n clud$4 ,9- clud$4 ---------------------------------------- --------------------- ,wr\ght-iron ma9 gird]s1 #fjj ,flange 44 #fc ,t5sion ,good4 plate ,wr\ght-iron ma9 gird]s1 #fdj 44 #fh ,good4 plate ,wr\ght-iron ma9 gird]s1 #gfj 44 #ge ,fair4 plate ,wr\ght-iron #gd #ig ma9 gird]s1 #bie #fc #hc ,compres-,good4 plate sion ,wr\ght-iron ma9 gird]s1 #fcj #ga ,t5sion ,fair4 lattice ,wr\ght-iron ma9 gird]s1 #dgj ,flange #ajj 44 ,compres- ,fair4 plate edge sion ,wr\ght-iron cross-gird]s1#bfj ,flange 44 #fg ,t5sion ,fair4 plate ,wr\ght-iron cross-gird]s1#aa4j #fc #fe ,bad2 loose plate rivets4 ,wr\ght-iron cross-gird]s1#aij #hd #ia ,good1 b plate ru/$4 ,wr\ght-iron cross-gird]s1#bbj #aje #aaa ,good1 b plate ru/$4 ,/eel tr\gh #aej ,fair1 gird] #ae4g,top edge #cbj ,compres-b sion ru/$4 ,/eel #ahg ,flanges #ge 44 ,t5sion ,fair1 tr\gh+ & ,com- b pression ru/$4 ---------------------------------------- --------------------- ,x w\ld be unwise to inf] f ! in/ances :i* h be5 quot$ t high /ress may be reg>d$ ) complaisance4 ,9 ! mo/ consci5ti\s eng9e]+ "w !re %\ld /ill be a lib]al m>g9 = mat]ial possibly defective1 or ev5 bad1 = wa/e & det]ioration1 & = ! aggregate effect ( m9or errors 9 design1 any "o ( :i* consid]ations1 except ! fir/1 by itself might n be ( great importance4 ,! conclusion :i* may1 h[ev]1 be d]iv$ f ?is & ! previ\s *apt]s is1 t bridge failures are less likely to occur f high /ress ( a k9d readily calculat$ ?an f failure 9 detail1 obscure & little suspect$1 ! reason = :i* is n p]haps app>5t1 till ! att5tion is =cibly direct$ to x by ! refusal ( ! /ructure to su/a9 ! =ces to :i* x may be liable4 ,,*apt] ,,vii4 ,,de=mations4 ,in/ructive lessons are to be _h f a /udy ( ! v>i\s alt]ations 9 =m to :i* metallic bridgework is liable1 :i* alt]ations may be due simply to ! developm5t ( /ress ( ord9>y am\nt1 & are !n g5]ally small2 or to abnormal /resses1 ! result ( "s di/ortion 9 ! bridge /ructure itself n orig9ally int5d$1 & possibly extreme4 ,9 addition to ^! !re may be de=mations due to settlem5t1 to 8creep+0 ( p>ts ( ! /ructure relative to ! re/1 to temp]ature *anges1 to ru/1 & to orig9al bad workman%ip4 ,9 any in/ance quot$ bel[ ! me?ods adopt$ to asc]ta9 ! am\nts ( su* alt]ations 7 q simple1 ev5 crude2 b z c>e 0 ex]cis$1 & no attempt made to measure any v m9ute *anges1 ! results may be accept$ z practically correct4 ,dismiss+ = ! pres5t *anges ( =m su* z are to be expect$1 & t\*$ ^u 9 o!r places 9 ?is "w1 ) respect to ! p>ticul> p>ts ( bridge /ructures affect$ by !m1 a few in/ances w be adduc$ ( alt]ations :i*1 ?\gh n v surpris+1 are su* z 9 ! design ( ! "w are h>dly likely1 9 mo/ in/ances1 to h be5 contemplat$4 ,a case has already be5 ref]r$ to 9 :i*1 ow+ to ecc5tric load+ ( ma9 gird]s1 ^! 71 z to ! top flanges1 flex$ sideways a consid]able am\nt4 ,x is propos$ to supplem5t ?is by fur!r rem>ks relative to some:at simil> cases4 ,a l effect is frequ5tly to be obs]v$ 9 tr\gh or tw9 gird]s1 9 :i* ! rails are support$ ^u longitud9al timb]s re/+ ^u project+ l$ges =m$ by ! bottom angle-b>s ( su* tr\ghs4 ,9 old =ms ( ?is arrangem5t x is common to f9d ! two gird]s =m+ ! tr\gh connect$ only by bolts pass+ ?r\gh ! timb]s1 or j above !m & bel[ ! rails2 or connect$ by n>r[ /rips1 :i* s]ve no o!r purpose ?an to prev5t ! sides spread+ at ! bottom4 ,! top flanges 9 su* cases commonly curve inw>ds on ! passage ( ! runn+ load1 accompani$ ( necessity by an increase ( compressive /ress ^u ! out] edges ( ! flanges1 & p]haps by ! work+ ( any flange-jo9t :i* may exi/4 ,?is1 bo? z to flex+ ( ! top flange & ! work+ ( a jo9t1 0 notic$ 9 ! case ( a bridge tw5ty-?ree ye>s old1 v simil> to t illu/rat$ 9 ,figs4 #h & #i1 & describ$ on pages #ac & #ad4 ,! top flange consi/$1 h[ev]1 ( a bridge rail rivet$ to ! top edge ( ! web1 butt+ at a jo9t1 & cov]$ by ?ick cov] /rips 7see ,fig4 #dh74 ,! jo9t itself 0 poor1 & dep5d$ l>gely ^u ! "* ( ! butt1 :i* 0 n suffici5tly good to prev5t ! top memb] k9k+ at ?is po9t1 "u ! jo9t influ5ce ( transv]se ef=t & compressive /ress1 ) possibly "s help f bolts pass+ ?r\gh timb] & webs1 ?\gh ^! be+ loose1 ! au?or does n ?9k !m at all responsible4 ,al?\gh n /rictly relevant1 x may be rem>k$ 9 pass+ t x is v objectionable to use bolts z 0 done 9 ?is in/ance2 = z ! timb] settles d[n on its seat1 tak+ ! bolts ) x1 ^! be> h>d 9 ! webs1 enl>g+ or ev51 z 9 ?is case1 te>+ ! holes1 accompani$ by injury to ! bolts !mselves4 ,! practice is n[ almo/ obsolete1 b ! example is in/ructive z %[+ ! impropriety ( secur+ timb]s by bolts pass+ ?r\gh !m at "r angles to ! action ( ! load1 unless ^! bolts are q free to move ) ! timb] z x compresses4 ,if tr\gh gird]s mu/ be us$1 ! bett] plan is to connect ! two sides by a cont9u\s bottom plate1 ! tr\gh ?us =m$ be+ prop]ly dra9$1 if ! timb] is n b$d$ 9 asphalt concrete2 or to introduce /iff diaphragms at int]vals b5ea? timb]s1 if ! dep? suffices4 ,9 ! case j quot$ ! curvature ( ! top memb]s ( ! gird]s 0 inw>ds1 b 9 ! in/ance giv5 bel[1 ( tw9 gird]s #bf feet effective span1 ) longitud9al timb]s betwe51 re/+1 z be=e1 ^u ! inn] l$ge =m$ by ! bottom flanges1 ! curvature 0 obs]v$ 9 ?ree out ( f\r gird]s to be #a_/b in* 9 a contr>y direction1 ! f\r? rema9+ /raight4 ,illu/ration3 ,,fig4 #dh4 ,illu/ration3 ,,fig4 #di4 ,an inspection ( ! accompany+ section1 ,fig4 #di1 w1 p]haps1 r5d] ! reason evid5t :5 x is notic$ t ! top memb]s are v unsymmetrical 9 =m1 ! effect ( ?is be+ to give ^! memb]s1 "u /ress1 a /rong t5d5cy to flex outw>ds1 app>5tly m ?an suffici5t to c\nt]act ! t5d5cy ( an ecc5tric application ( load on ! bottom flange to br+ !m inw>ds4 ,x is to be obs]v$ t ! ecc5tricity ( ! flange appe>s to be n mat]ially 9 excess1 & is actually s1 only because ! ?9ness ( ! web--#a_/d in*--r5d]s x incompet5t to keep ! bottom flange up to its "w1 & s secure ! full effect ( ! ecc5tric load+ 9 limit+ ! outw>d t5d5cy1 due to ! section ( ! top memb]1 ! effects ( :i* are ?us m app>5t ?an w\ld h be5 ! case ) a /iff] web4 ,ties across f "o bottom flange to ! o!r prev5t ! want ( symmetry notic$ 9 ^!--:i*1 by ! way1 is on ! wrong side = utility--f hav+ any p>ticul> effect4 ,to give "o o!r example ( ! consequ5ces ( ecc5tric load+1 a bridge ( #dh feet effective span may be quot$4 ,?is bridge c>ri$ f\r l9es ( way support$ by five ma9 gird]s1 truss$ by kick+-/ruts 9 su* a mann] z to =m a ba/>d ar*4 ,a "p section & plan are giv5 9 ,figs4 #ej & #ea4 ,illu/ration3 ,,fig4 #ej4 ,illu/ration3 ,,fig4 #ea4 ,! floor consi/$ ( ,l9dsay's tr\gh+ re/+ ^u ! l[] flanges ( ! ma9 gird]s1 ! ?ree middle gird]s1 subject to ecc5tric load+1 sometimes on "o side1 sometimes on ! o!r1 71 ) dead load only1 /raight2 b ! two out] gird]s1 liable to load+ only on "o side1 _h1 "u repeat$ applications ( su* a load1 assum$ a p]man5t curve t[>ds ! rails--#ac_/af in* 9 "o case & #a in* 9 ! o!r--:i* curvature1 no d\bt1 increas$ :5 a live load came ^u ! contigu\s roads1 ?\gh ?is 0 n measur$4 ,x %\ld be rem>k$ 9 pass+ t1 ow+ to settlem5t & ! cant+ ( ! abutm5ts1 ! ?ree middle gird]s 7 also 8d[n0--9 "o case #c_/d in*4 ,! gird]s1 ) "o ne> road load$1 deflect$ #a_/h in*--greatly less ?an w\ld h be5 ! case _h ! ma9 gird] n be5 truss$4 ,! bridge1 at ! "t ^! p>ticul>s 7 obta9$1 _h be5 9 exi/5ce six ye>s4 ,de=mations due to settlem5t may be v consid]able4 ,! au?or recalls two in/ances affect+ cont9u\s gird]s4 ,9 ! fir/ ( ^!1 a bridge tw5ty ye>s old1 ( two spans ( ab\t #ej feet ea*1 & ) gird]s #d feet #f in*es deep1 ! c5tre pi] _h sunk #d in*es1 r$uc+ ! spans1 z respects ! dead load1 practically to ! condition ( simple beams1 j re/+1 b h>dly be>+1 ^u ! pi]s :5 free ( live load4 ,9 ! second case1 also ( two op5+s ( ab\t #ee feet ea*1 ) gird]s #h feet deep1 "o abutm5t _h sunk ab\t #c in*es1 m ?an d\bl+ ! /resses ov] ! c5tre pi]4 ,x is manife/ t cont9u\s gird]s %\ld only be adopt$ :]e settlem5t ( ! support+ po9ts is n likely to occur to any mat]ial degree4 ,if ?is _c be reli$ ^u1 ! !oretical flange sections may h>dly be work$ to ) any prud5ce2 x be+ !n advisable to make a lib]al all[ance = settlem5t /resses1 9 :i* case any economical advantage t %\ld exi/ w probably disappe>4 ,x is1 h[ev]1 to be ackn[l$g$ t s long z ! gird]s are 9 t\*1 "u dead load1 ) ! be>+s int5d$ to support !m1 ! /resses due to a live load are unalt]$1 ! pr9cipal effect 9 ?is case be+ t ! v>iation 9 /ress due to ! live load ranges betwe5 limits t are high] or l[] 9 ! scale ( /ress ?an is ! case ) be>+s undi/urb$2 /ill1 if x is desir$ t ! maximum /ress %all n exce$1 say1 #f tons p] squ>e in*1 x c h>dly be a matt] ( indiff]5ce t settlem5t %all induce a maximum (1 p]haps1 #aj tons1 z 9 t case ! /ress mu/ be #d tons ne>] ! limit ( /atical /r5g?4 ,be=e leav+ ?is matt] x may be well to po9t out t 9 ! case ( cont9u\s gird]s ( uni=m section a mod]ate settlem5t ( ! pi]s may ev5 be advantage\s by r$uc+ ! mom5ts ov] ! pi]s1 & possibly mak+ !m equal to ^? obta9+ ne> ! middle ( ! spans1 9 :i* case !re w be less inequality ( /ress 9 ! booms & a r$uction ( ! maximum /ress4 ,bridges consi/+ ( simple ma9 gird]s connect$ by cross-gird]s may be v prejudicially affect$ by unequal settlem5t2 = in/ance1 if "o gird] be>+ settles m ?an ! o!rs1 a twi/ is put ^u ! /ructure v try+ to ! floor-gird] connections1 & possibly to ! ma9 gird]s2 to ! web if a plate gird]1 or to ! v]ticals if an op5-webb$ truss ) rigid cross-gird] atta*m5ts4 ,inde$1 settlem5t ( ?is k9d may be mu* m de/ructive to a metallic bridge ?an to an ar* ( brick or masonry1 ! commonly accept$ op9ion not)/&+4 ,in/ances ( de=mations due to ! creep+ ( "s "p ( ! /ructure away f its "w1 are )9 ! au?or's k1 r>e2 except 9 ! case ( ! ends ( ma9 gird]s 9 skew bridges1 already ref]r$ to4 ,di/ortion1 ! result ( temp]ature *anges1 is frequ5tly to be obs]v$ 9 any consid]able l5g? ( gird] flange or p>apet :]e !re is n fre$om ( movem5t1 unless due provision is made to *eck x4 ,x is q common to see p>apets out ( l9e1 ei!r because ! ends are n free1 or because ! light "w ( ! p>apet be+ m expos$ to ! sun's rays ?an ! gird] "w to :i* ! l[] "p is atta*$1 exp&+ to a great] degree1 is subject to consid]able compressive =ce1 & buckles "u its influ5ce4 ,! cure = ?is condition is obvi\sly to provide su* p>apets ) free or flexible jo9ts at mod]ate di/ances ap>t1 or to make ! p>apet suffici5tly /iff to take ! /resses develop$1 )\t crippl+4 ,a p>apet may also g out ( %ape if directly atta*$ to ! top flange ( a gird] liable to heavy load+1 p>ticul>ly if ! gird] be %all[] ?an ! p>apet1 simply by its inability to ma9ta9 tru? ( l9e "u ! compressive /ress1 :i* x %>es ) ! top flange ( ! gird] prop]4 ,rivets spac$ too f> ap>t1 by all[+ ! plates or o!r p>ts to spr+ op5 slightly1 & p]mitt+ moi/ure to ent]1 results 9 ! gr[? ( ru/1 :i*1 z x swells 9 =m+1 =ces ! p>ts asund]1 & may set up consid]able /ress4 ,flat b>s rivet$ toge!r by rivets spac$ #ab in*es ap>t may f ?is cause be =c$ asund]1 z mu* z #a_/b in*1 suffici5t to set up a /ress1 ) any practicable ?ickness ( b>1 mu* exce$+ ! ela/ic limit4 ,local di/ortions may occur z ! result ( imp]fect workman%ip or c>eless erection1 caus+ q possibly v sev]e local /resses2 or gird] flanges may be out ( /raight z a result ( rivet+ up along "o side fir/1 in/ead ( advanc+ ! rivet+ simultane\sly along ! :ole bread? ( ! flange4 ,! injury done by drift+ is well kn[n1 & !re is reason to ?9k consid]able damage is sometimes done to gird]work dur+ manufacture by r\gh treatm5t to make ! "w come toge!r2 b ! au?or has little to (f] ) respect to ^! matt]s t is n common k4 ,x may1 h[ev]1 be po9t$ out 9 pass+ t a bridge ^u ! design ( :i* great c>e has be5 exp5d$1 ) ! idea t !oretical propriety %all n be violat$1 may be completely spoil$ 9 ?is respect by c>eless con/ruction4 ,=tunately1 bo? /eel & wr\ght iron1 if ( good quality1 are long suff]+4 ,incompet5t erection w sometimes result 9 ! true gird] camb] n appe>+1 or 9 diff]5ces z betwe5 gird]s suppos$ to be simil>4 ,?is is n1 ( c\rse1 a de=mation 9 ! s5se 9 :i* ! ^w has previ\sly be5 us$1 b x is desirable to be> ! fact 9 m9d z a possible cause ( defective camb] 9 deal+ ) que/ions ( de=mation4 ,! =ego+ has ref]5ce *iefly to alt]ations ( =m 9 bridgework ( wr\ght iron or /eel1 b a case ( consid]able int]e/ is t ( a ca/-iron ar*$ /ructure1 ( :i* ! au?or made a v complete exam9ation4 ,illu/ration3 ,,fig4 #eb4 ,illu/ration3 ,,fig4 #ec4 ,?is bridge1 built 9 #ahci1 & c>ry+ two l9es ( railway1 consi/$ ( ?ree spans1 #ajj feet ea*1 ( #aj feet rise1 made up ( f\r inn] & two out] ribs1 ea* rib be+ 9 ?ree ne>ly equal p>ts2 ! floor 0 ( timb]1 ! abutm5ts & pi]s ( masonry4 ,z orig9ally con/ruct$ !re 0 no brac+ betwe5 ! ribs o!r ?an ! frames indicat$ on ! plan "h giv5 7,fig4 #eb71 /ret*+ f out] rib to out] rib 9 ! neighb\rhood ( ! rib jo9ts1 :i* 7 simple butts )\t bolts or any equival5t means ( connection4 ,! floor 01 h[ev]1 brac$ 9 ! horizontal plane1 & ! /ructure 0 also brac$ ov] ! masonry pi]s4 ,aft] =ty-two ye>s' use supplem5t>y di/ance-pieces 7 introduc$ betwe5 ! ribs1 b /ill no brac+ betwe5 !m1 or any effici5t means ( *eck+ lat]al movem5t4 ,a crack develop+ 9 "o ( ! out] ribs at ! cr[n1 l$ to an inve/igation to trace ! cause1 ! bridge !n be+ fifty-f\r ye>s old4 ,c>eful plumb+ ( ! abutm5ts reveal$ ! fact t ?ree out ( f\r abutm5t pila/]s 7 out ( ! v]tical1 z %[n 9 ,figs4 #eb & #ec1 ! greate/ am\nt be+ #e_/h in* 9 #f feet--at t corn] f :i* ! crack$ rib _h its spr++2 !re 0 also o!r evid5ce ( settlem5t 9 an old crack ext5d+ f ! top ( ! abutm5t to ! gr\nd level1 al?\gh ?is movem5t 0 v old1 c]ta9ly z to ! great] "p4 ,! ribs ( ?is span 7 also out ( plumb1 t :i* 0 crack$ be+ #b-a_/b in*es out at ! c5tre4 ,! jo9ts ( ! ribs1 :i*1 z already /at$1 7 simple butts1 9 "s cases op5$ & %ut1 z ! load pass$ ov]1 9 su* a way z to sugge/ t ! ribs 7 act+1 9 a mann]1 z f\r-h+$ ar*es1 ( :i* two h+es 7 at ! spr++1 & ! o!r two at ! jo9ts1 "o ( :i* w\ld = mo/ positions ( ! load be out ( use1 r$uc+ ! rib to ! ?ree-h+$ condition2 9 o!r words1 z ! roll+ load pass$ ov] ! span1 "o or o!r ( ! two jo9ts ( a rib w\ld 8gape0 an appreciable am\nt at ! bottom or at ! top4 ,obs]vations 7 tak5 by means ( a !odolite plac$ bel[1 ei!r ^u ! bank or ^u ! tops ( ! masonry pi]s1 sight+ ^u suitable scales atta*$ to ! ribs to asc]ta9 ! am\nts ( v]tical & horizontal movem5t dur+ ! passage ( tra9s ov] ! bridge4 ,! pr9cipal results are set =? 9 ! foll[+ table3-- ,,movem5ts ,,( ,,ca/-,,iron ,,ribs ,,"u ,,live ,,load ,,9 ,a ,,bridge ,,( ,,?ree #ajj-;,,ft4 ,,spans4 ---------------------------------------- ---------- ,fall 9 ,rise 9 ,lat]al -- ,in*es4 ,in*es4 ,movem5t 9 ,in*es4 ---------------------------------------- ---------- ,span ,no4 #a4 ,at ,a4 ,up road load$ #bj #jh #jd ,a4 ,d[n road load$ #jh #jc #jd ,b4 ,d[n road load$ #ad ,no record4 #jb ,span ,no4 #b4 ,at ,c4 ,up road load$ #dj #ac ,slight4 ,c4 ,d[n road load$ #aj #je ,span ,no4 #c4 ,at ,d4 ,up road load$ #bb ,no record4 ,no record4 ,d4 ,d[n road load$ #ae ,slight4 ,slight4 ---------------------------------------- ---------- ,,note4--,! lat]al movem5ts are to ei!r side ( ! mean position4 ,! p>ticul>s = spans #b & #c 7 obta9$ ) ! in/rum5t set up on ! pi] betwe5 ^! spans4 ,! tremor ( ?is pi] 0 su* t no useful read+s = lat]al movem5t c\ld be obta9$4 ,fur!r1 z ! roll+ load came ^u ^! spans1 ! effect 0 to rock ! pi] to an ext5t vitiat+ ! read+s = v]tical displacem5t2 b by sight+ ^u ! fix$ abutm5t1 & obs]v+ ! am\nt ( ?is rock+1 suitable corrections 7 made 9 ! app>5t rib movem5ts4 ,! figures giv5 9 ! table are ?us correct$4 ,! pi] rock+ 0 equival5t1 z an extreme1 to an incl9ation f ! v]tical ( #a 9 #cbjj4 ,an attempt to measure ! horizontal movem5t ( ! pi]-top 0 unsuccessful1 ow+ to ! impracticability ( sett+ up ! in/rum5t 9 a suitable position1 suffici5tly ne> to ! pi] to enable read+s to be satisfactorily tak54 ,?is horizontal displacem5t probably am\nt$ to ab\t #a_/af in* ei!r way4 ,! rise & fall ( ! ar*es1 & rock+ ei!r way ( ! pi]s1 v>i$1 z might be expect$1 9 accordance ) ! position ( ! runn+ load ) respect to ! spans4 ,summ>is+ ! results1 ! greate/ v]tical movem5ts d[nw>ds 7 #jbj in*1 #jdj in*1 & #jbb in* = spans ,nos4 #a1 #b1 & #c1 ! upw>d movem5ts be+ #jjh in* & #jac in* = ! fir/ & second spans1 !re be+ no record$ result ( ?is k9d = ! ?ird span4 ,) adjac5t ribs load$1 ! movem5t ( ! ribs unload$ 0 "o f "o-?ird to "o-half ( ! full am\nts4 ,x is to be not$ t ! lat]al displacem5t 9 no case exce$$ #jjd in* ei!r way1 nor 7 ! v]tical movem5ts exceptional2 yet1 z a matt] ( s5sation1 :5 seat$ ^u ! ironwork1 x 0 a little difficult to believe !m really s mod]ate4 ,obs]vations 7 also made to asc]ta9 ! rise ( ! ar*es f w9t] to summ] temp]atures1 ) ! result t ?is 0 f\nd to be #jde in*1 #jde in*1 & #jee in* = ! spans 9 ord]1 ! extreme temp]atures be+ fairly repres5tative ( ! ,engli% w9t] & summ]4 ,! /ructure 01 z a consequ5ce ( ! exam9ation1 effici5tly brac$ by diaphragms betwe5 ! ribs1 & diagonals foll[+ ! ar* ribs r\nd f spr++ to spr++1 ) satisfactory results4 ,! crack already ref]r$ to1 & its probable causes1 w be dealt ) "u 8,ca/-,iron ,bridges40 ,ev5tually ?is bridge 0 recon/ruct$ to meet ! requirem5ts ( gr[+ eng9e-loads4 ,,*apt] ,,viii4 ,,deflections4 ,deflection1 consid]$ only z a fraction ( ! span1 & )\t reg>d to o!r conditions affect+ x1 is ( v little use z an indication ( a gird]'s fitness = its "w2 b :5 tak5 ) ref]5ce to ! dep? ( ! gird]1 ! nature & am\nt ( ! load produc+ flexure1 &1 fur!r1 ) reg>d to ! quality ( ! workman%ip & normal prop]ties ( ! mat]ial ( :i* ! beam is con/ruct$1 x may be ( "s little s]vice 9 help+ to =m a reliable op9ion4 ,?is consid]ation applies ) less =ce1 p]haps1 to new "w ?an to old1 9 :i* !re may be unkn[n influ5ces at "w1 or unkn[n defects :i* by excessive deflection may be betray$4 ,?\gh too mu* importance %\ld n be atta*$ to results ( deflection te/s 9 any "o in/ance1 yet ! practice ( obs]v+ su* movem5ts1 & consid]+ !m ) ref]5ce to ea* case1 gives a good g5]al idea ( :at may be expect$ 9 a fre% in/ance1 any mat]ial dep>ture f :i* %\ld be a reason = specific inquiry z to ! cause4 ,a fur!r reason ) new "w is f\nd 9 ! evid5ce x af=ds z to :e!r ! loads c>ri$ travel to ! supports really z int5d$1 or by "s r\te n contemplat$2 or1 9 ! case ( floor beams1 9 :at way ! load is di/ribut$ among/ !m1 if1 inde$1 !re be any su* di/ribution4 ,! au?or has commonly f\nd t new "w gives great] deflections ?an old--i4e41 :ile calculation gives ! same result = ea*1 x does n apply equally well to bo?4 ,! diff]5ces may be accid5tal1 b are probably due to o!r causes1 p]haps to ! fact t new "w has n by repeat$ applications ( load lo/ ! resili5ce ( p>ts liable to consid]able local /ress1 su* z is v liable to occur at connections1 s t ! deflection is1 :il/ new1 great] ?an aft] _m ye>s' use1 by :i* "t su* p>ts may develop a def9ite 8set10 & contribute 9 a less degree1 or n at all1 to ! total ela/ic de=mation4 ,x is also possible1 z already sugge/$1 t repeat$ high /ress may r$uce ! ratio ( /ra9 to /ress1 ! mat]ial gradually becom+ m rigid1 ! modulus ( ela/icity be+1 9 fact1 increas$4 ,9 gird]s ( ord9>y con/ruction1 ! major "p ( ! deflection is due to ! booms1 ! rema9d] to ! web2 ! latt] is = plate gird]s a small am\nt only1 & is commonly neglect$1 b = op5 web con/ructions x may be q appreciable4 ,= any giv5 type ( web arrangem5t ! deflection due to ! web w1 = all dep?s1 rema9 a con/ant quantity = ! same span & unit /ress2 & ?\gh a mod]ate fraction ( ! :ole deflection = a %all[ gird]1 x may be a v consid]able "p = a gird] ( great dep?1 9 :i* t "p due to ! booms is1 ( c\rse1 small]1 s9ce ! deflection due to ^! v>ies inv]sely z ! gird]s' dep?s4 ,deflection1 be+ dep5d5t ^u ! ela/icity ( ! mat]ial1 is ( necessity v l>gely influ5c$ by ! value ( its modulus ,e1 itself liable to consid]able v>iation1 & is increas$ 9 a small degree by ! yield ( jo9ts & rivets1 :i* effect1 ap>t f ! initial 8set0 ( ! gird]s1 appe>s to be negligible4 ,! /iffness ( memb]s 9 resi/+ angul> di/ortion at connections mu/ also1 = op5-web rivet$ /ructures1 affect ! result1 mak+ x some:at less1 &1 f9ally1 section excess at jo9ts & gusset atta*m5ts has an influ5ce 9 modify+ deflection z comp>$ ) t due to ! normal gross sections simply4 ,f ^! consid]ations x is app>5t t any simple deflection =mula mu/ be l>gely empiric 9 its nature4 ,= plate gird]s ( uni=m dep? & flange /ress1 ! writ] has f\nd ! foll[+ to give good results3-- ,s#b ----- f deflection 9 in*es4 ,d ,c ,! span ,s & dep? ,d are1 z a matt] ( conv5i5ce1 tak5 9 feet2 ! con/ant ,c is = wr\ght iron #cejj1 & = mild /eel #djjj2 f is ! mean ( ! extreme t5sile & compressive /resses ( ! booms1 9 tons p] squ>e in*1 e/imat$ ^u ! gross sections4 ,?is1 ?\gh satisfactory = plate gird]s1 is n s suit$ to gird]s hav+ op5 webs1 9 :i* ! deflection w m ne>ly be 7#c,s ,s#b 7 7-- -----7 f1 7,c ,d ,c7 ! con/ant ,c be+ #cijj & #ddej = iron & /eel respectively4 ,! latt] values ( ,c correspond to normal values ( ! modulus ( ela/icity ( #aa1gjj & #ac1cej tons = iron & = /eel1 x be+ assum$ t any slight rivet yield is (f-set by any small section excess--say1 #e p] c5t42 x may1 h[ev]1 happ5 t section excess is great] ?an assum$1 9 :i* case "s all[ance may prop]ly be made = ?is by increas+ ,c4 ,to adapt ! =mul to gird]s o!r ?an ^? hav+ p>allel booms & uni=m /ress1 ! results1 z d$uc$ above1 may be multipli$ by con/ants giv5 9 column ,b ( ! ,table giv5 on page #ic4 ,! practice ( adopt+ = ,e 9 deflection =mul a quantity mu* small] ?an its nom9al am\nt1 ) ! object ( all[+ 9 rivet$ gird] "w = ! yield ( rivets & ( jo9ts1 c h>dly n[ be def5d$1 :atev] may h be5 a case at a "t :5 workman%ip 0 mu* inf]ior1 :5 !re 0 no ma*9e rivet+1 & jo9ts 71 ow+ to ! small weight ( plates & b>s1 ?ree times z num]\s4 ,! initial 8set0 ( a gird] consequ5t ^u fir/ load+ is a quantity q di/9ct f deflection prop]1 & may be s small z to be negligible1 or read #aj p] c5t4 ( ! true deflection1 v>y+ ) design & workman%ip4 ,no e/imate ( gird] deflection c be ev5 approximately true if !re is1 at ! level ( ! top or bottom flanges1 a plat$ or o!rwise rigid floor sy/em :i* is n tak5 into acc\nt1 z ?is w h ! effect ( v mat]ially r$uc+ ! boom /ress4 ,to neglect ?is influ5ce1 :]e x exi/s1 mu/ necess>ily lead to disappo9t+ results1 & x is q practicable 9 _m in/ances to include x 9 ! calculation4 ,! influ5ce ( angul> di/ortion betwe5 ! v>i\s memb]s has be5 neglect$4 ,x may be po9t$ out1 h[ev]1 t ! resi/ance accompany+ ^! movem5ts 9 gird]s hav+ rivet$ connections1 ?\gh unimportant z affect+ deflection1 is wor? "s consid]ation 9 reg>d to second>y /ress4 ,= gird]s ( simil> type & unit /ress ^! angul> v>iations w be ! same 9 am\nt = any span1 b w g5]ally be ( less importance 9 l>ge gird]s ?an 9 small1 because 9 l>ge gird]s ! ratio ( ! bread? ( memb]s to _! l5g? is commonly less4 ,:5 det]m9+ ! probable deflection ( any gird] ( exceptional figure1 x w be f\nd conv5i5t to make a /ra9 diagram--an old device1 9 :i* ! actual alt]ations ( l5g? be+ asc]ta9$ = all memb]s1 ! gird] is c>efully set out to a suitable scale1 ) ! l5g?s ( memb]s increas$ or r$uc$ by ! actual e/imat$ am\nts4 ,! di/ort$ figure result+ w !n give ! probable deflection4 ,! value ( ,e = ?is purpose %\ld nev] be tak5 at less ?an ! normal am\nt1 & may = a consid]able excess ( metal 9 jo9ts & gussets be made z mu* z #aj p] c5t4 great]1 ?is be+ a conv5i5t means ( mak+ ! necess>y correction4 ,! effect ( loads quickly appli$ may "h be consid]$ 9 connection ) ela/ic de=mations ( gird]s ( ! same span1 b diff]5t dep?s4 ,if ^! be design$ = simil> loads & unit /resses1 ! deflections due to webs & booms ( ! gird]s comp>$ w be> ! same relation1 ea* to ea*1 z d ! weights1 :e!r 9 bo? cases ! loads be in]t or quickly appli$1 f :i* x foll[s t ! me*anical 8"w0 done by ! loads 9 fall+ ?r\gh ! deflection heights is1 neglect+ in]tia1 always 9 proportion to ! gird]work weights1 & is a simil> am\nt p] ton1 :i* z ! total l5g? ( memb]s rema9s sub/antially unalt]$1 corresponds to a simil> am\nt ( "w p] unit ( section1 or simil> /ress1 irrespective ( ! dep? ( ! gird]s4 ,b = a 8drop0 load1 z :5 !re is "s ob/ruction ^u a railway bridge1 !re w be 9 addition a fur!r am\nt ( "w to be absorb$1 :i* is to be consid]$ ! same :atev] ! gird]'s dep?1 & w = deep gird]s be a l>g] am\nt p] ton ( gird]work ?an 9 ^? t are %all[2 ?is1 tak+ effect on memb]s ( ! same aggregate l5g?1 b light]1 w develop a high] /ress ?an 9 gird]s ( less] dep?1 m p>ticul>ly 9 ! booms4 ,! influ5ce ( ! gird]'s in]tia 9 modify+ drop-load effects w also be less m>k$ 9 deep--i4e41 light--gird]s ?an 9 gird]s %all[ & heavy4 ,x is1 not)/&+ all ?is1 desirable t ! dep? ( ma9 gird]s %\ld be lib]al = economy's sake1 & also t ( floor beams1 = reasons already dealt )2 ! probability ( ! drop load is some:at remote1 &1 ?\gh possible1 w\ld simply induce1 if x occurr$1 an increm5t ( /ress r m important 9 deep gird]s1 mak+ x specially desirable 9 ^! to give p>ticul> att5tion to ! detail+ ( any connections liable to suff] f impact effects4 ,x %\ld be rem>k$ t = %ort & v flexible beams1 g5]ally outside ! limits ( practice1 !re may also be1 "u quickly mov+ loads1 a mat]ial increase ( /ress due to ! c5trifugal ef=t ( ! load on runn+ r\nd ! deflection curve1 & 9 ris+ ^u ! /eep "p ( ! curve beyond ! gird]'s c5tre4 ,:]e advisable1 ^! effects may be modifi$ by camb]+ ! rail4 ,= p9 bridges 9 :i* !re may be spr+ 9 ! p9s1 excess /ress 9 "s eye-b>s due to inequalities ( l5g?1 & a want ( t rigidity peculi> to rivet$ /ructures1 ! deflection w be great] ?an above indicat$ = gird]s ( ! ord9>y ,engli% type4 ,! me?od 9 common use = measur+ ! deflections ( gird]s b a mod]ate di/ance above ! gr\nd by means ( slid+-rods1 ?\gh crude1 gives1 ) c>e1 results suffici5tly accurate = mo/ practical purposes2 b "s po9ts necess>y to rememb] may be m5tion$ ) propriety4 ,! l[] rod %\ld re/ firmly ^u some?+ solid1 say a /one1 well b$d$ & free f any t5d5cy to rock2 ! upp] end %\ld be> aga9/ "s "p ( ! gird] above1 pres5t+ a h>d surface1 free f dirt or scale1 & z ! runn+ load approa*es ! bridge x %\ld be asc]ta9$ t !re is no slack1 t ! rods be> h>d at ! top & bottom4 ,! upp] end hav+ be5 depress$1 c>e is to be ex]cis$ to make sure ( ! read+ be=e ! rods alt] _! relation to ea* o!r4 ,^! precautions are s self-evid5t t an apology is almo/ necess>y = m5tion+ !m4 ,to asc]ta9 deflections ) a s+le pair ( rods is only all[able :5 ! gird]s re/ firmly on _! be>+s2 if felt has be5 plac$ "u ! gird] ends1 or if ! b$/ones are insecure or rock+1 x is necess>y to use ?ree pairs ( rods1 "o pair at ! middle & a pair at ea* end1 9 :i* case ! mean ( ! two end read+s mu/ be d$uct$ f ! read+ ( t at ! c5tre to get ! desir$ result4 ,9 ! case ( a numb] ( spans 9 s]ies1 ea* re/+ ^u sill gird]s common to two sets ( be>+s1 ?is me?od also gives results ( indiff]5t reliability1 z ! depression ( ea* end may be great] z ! travell+ load comes ^u & leaves ! span ?an :5 x is precisely ov] ! middle1 & x is 9 g5]al out ( ! "q to secure by ?is mode simultane\s read+s = a p>ticul> position ( ! runn+ load1 :i* are :at is requir$4 ,! au?or sugge/s1 z a means ( asc]ta9+ deflections free f ^! objections1 t x %\ld be done by fir/ measur+ ! slope at "o end1 & f ?is d$uc+ ! deflection at ! c5tre4 ,?is is to be accompli%$ by means ( a little in/rum5t1 consi/+ ( a telescope ) cross-hair sights1 & fitt$ ) a reflect+ prism at ! eye-piece capable ( be+ turn$ r\nd1 s t ! obs]v] has a wide *oice z to ! position he assumes ) ref]5ce to ! in/rum5t1 & may look ei!r directly ?r\gh x1 or at "r angles to ! axis ( ! telescope4 ,?is is clamp$ at "o end ( ! gird] ov] ! be>+1 at ! o!r end a scale is secur$1 to :i* ! telescope is direct$1 ! cross hair be+ made to sight on ! z]o ( ! scale1 or ! read+ not$4 ,= a gird] suppos$ to deflect to uni=m curvature 7say1 ) uni=m dep? & uni=m /ress1 ! ord9>y case7 ! read+ obs]v$ w be f\r times ! deflection2 e #a_/aj in* actual read+ on ! scale w correspond to #a_/dj in* ( gird] deflection4 ,ap>t f ! deflection1 ?is me?od gives a ready means ( obs]v+ ! end slope1 a quantity ( equal value = purposes ( comp>ison4 ,z ) gird]s ( simil> proportions1 & simil>ly /ress$1 ! deflection w at all spans be ! same fraction ( ! span2 s %\ld ! end slope be a con/ant quantity "u simil> conditions1 ! diagram1 ,fig4 #ed1 w make ! pr9ciple q cle>4 ,illu/ration3 ,,figs4 #ed to #eg4 ,/rictly ! "* ( ! deflection curve is slightly modifi$ by t "p ( ! deflection due to ! web2 s t ! depression at ! c5tre w\ld1 9 ! case assum$ above1 be some:at m ?an "o-f\r? "p ( ! end read+1 & g5]ally w be a l>g] fraction ( ! read+ ?an t d$uc$ f a consid]ation ( flange /ress simply4 ,9 ,figs4 #ee to #eg1 :i* are int5d$ to expla9 ?is1 x w be notic$ t deflection due to ! web is %[n /raight-l9$ f ! be>+s to ! c5tre ( ! gird]2 ?is is /rictly true only = a gird] correctly design$ = an immovable di/ribut$ load2 b z !re %\ld be = gird]s int5d$ = a travell+ load1 "s excess 9 web memb]s ne> ! c5tre "u ! condition ( uni=m load+1 ! po9t ( ! figure %\ld be r\nd$ (f to be 9 agreem5t ) ?is case1 ?\gh x is left z %[n 9 ! diagram = ! sake ( simplicity4 ,suitable con/ants1 includ+ ! corrections necess>y1 are giv5 9 column ,a ( ! table annex$ = a few typical cases1 & by ^! con/ants ! actual read+s %\ld be multipli$ to f9d ! deflection4 ,! con/ants h be5 work$ out = dep?s ( "o-t5? ! span2 = great] dep?s !y %\ld be slightly m1 & = small] dep?s some:at less1 b !y may be us$ betwe5 ! limits ( "o-six? & "o-f\rte5?1 ) a maximum error h>dly exce$+ #e p] c5t41 & g5]ally mu* less4 ,! figures 9 column ,b relate to ! =mul previ\sly /at$1 & apply equally well to all dep?s4 ,,tables ,,( ,,multipli]s ,,= ,,deflection4 ,uni=m ,/ress3 ,a4 ,b4 ,gird]s ( uni=m dep?1 v>y+ flange section #jbg #ajj ,hog-back$ gird]s1 ends half ( c5tre dep?1 v>y+ flange section #jbd #ajh ,v>y+ ,/ress3 #a;,gird]s ( uni=m dep? & flange section #jcb #jhg #a;,hog-back$ gird]s 7z above71 b uni=m flange section #jbi #jig #a;,b[-/r+ gird]s ( uni=m flange section #jaf #acj ,footnote #a3 ,= uni=m load+4 ,x is app>5t t1 if pref]r$1 ! scale1 in/ead ( be+ 9 in*es1 divid$ suitably1 may1 = ea* type ( gird]1 be amplifi$ to ! prop] degree1 s t ! am\nt ( ! deflection may be read (f at once4 ,?is me?od ( deal+ ) deflections is q indep5d5t ( ! "* ( ! be>+s1 & is applicable to gird]s at any height above gr\nd or ov] wat]2 b its use w\ld h>dly be practicable = v small beams1 or ^? 9 an awkw>d position1 or ne> :i* x w\ld be impossible to rema9 ) a runn+ load ^u ! bridge4 ,!re is a possible s\rce ( error 9 ! use ( ! in/rum5t1 mo/ likely to occur ) triangulat$ gird]s1 ) :i*1 if ! in/rum5t is plac$ at ! top ( an end po/1 ! read+ obs]v$ may be ! jo9t effect ( deflection & ( local flexure ( ! memb]s meet+ ne> ! telescope4 ,?is may be te/$1 &1 if necess>y1 all[$ =1 by fir/ sight+ ^u a scale at ! next apex1 & obs]v+ ! effect ( ! mov+ load4 ,aga91 z gird]s sometimes cant t[>ds ! runn+ load1 if ! in/rum5t is plac$ on "o edge ( a gird]1 & ! cant+s ( ! two ends are dissimil>1 a false read+ w result1 :i* may be am5d$ by asc]ta9+ ! am\nt ( cant at ea* end1 & correct+ = ! effect ( ! diff]5ce betwe5 ! cants ^u ! obs]vation4 ,only 9 exceptional cases is x likely t ei!r ( ^! consid]ations w\ld ne$ att5tion4 ,! au?or has secur$ ) ?is in/rum5t v promis+ results1 not)/&+ t "u a runn+ load !re is a slight haz9ess ( ! scale z se5 ?r\gh ! telescope1 due to 8di!r10 l>gely ! result ( imp]fections :i* may be rem$i$4 ,deflections may sometimes be conv5i5tly tak51 by a quick-ey$ obs]v]1 ) a good surveyor's level & a specially-divid$ /aff held at ! c5tre ( ! gird]4 ,! divisions pref]r$ by ! au?or = ?is purpose are #a_/aj in*1 pla9ly m>k$1 :i* may be se5 at #ej feet di/ance ) suffici5t cle>ness to make possible read+s by e/imation betwe5 ! divisions to1 say1 #a_/ej in*4 ,b x is cle>ly desirable n to rely ^u a s+le obs]vation only1 :]e all ! evid5ce is gone s soon z ! sight has be5 tak54 ,9 rail-be>]s1 or o!r %ort gird]s1 x may n be practicable to adopt su* me?ods1 ei!r on acc\nt ( an inability to f9d a suitable place = ! in/rum5t1 or to read ) any telescope ) suffici5t promptitude z ! load passes rapidly ov]4 ,! use ( rods may also be out ( ! "q1 z ! errors att5d+ _! manipulation may be s]i\s :]e b a small movem5t has to be not$1 ?is be+ complicat$ 9 "s in/ances by ! be>+s be+ insecure1 & work+ to an ext5t :i* obscures ! measurem5t s\ght4 ,9 su* cases x is pref]able to use a /iff slat ly+ along ! gird]1 :i* be>s1 ?r\gh %ort blocks ov] ! gird] be>+s1 ^u ! flanges2 ! deflection is !n read by direct measurem5t ( ! gird]'s depression at ! c5tre1 relative to ! slat4 ,! au?or is1 un=tunately1 n able to give any precise in=mation on ! effect ( runn+-load z aga9/ a load t is /ation>y 9 connection ) gird] deflections4 ,x is by no means easy 9 ord9>y "w ^u a railway to secure facilities = mak+ su* comp>ative te/s4 ,x may1 h[ev]1 be confid5tly /at$1 z a result ( su* obs]vations z he has made1 t ! deflection due to a load com+ rapidly ^u a bridge is1 z to ! ma9 gird]s (1 say1 a #ej feet span1 b little great] ?an t due to ! same load /ation>y2 x may be1 p]haps1 #e to #aj p] c5t4 m4 ,x is evid5t t to det]m9e ! precise diff]5ce :]e ! quantity to be measur$ is s small ne$s app>atus ( a m delicate "* ?an t 9 common use1 & ! control ( an eng9e1 or eng9es1 = ! purpose ( mak+ ! special te/s1 conditions :i* on a busy l9e c only be secur$ by special arrangem5ts previ\sly made4 ,,*apt] ,,ix4 ,,decay ,,& ,,pa9t+4 ,! au?or has collect$ p>ticul>s z to ! am\nt & rate ( ru/+ 9 metallic /ructures :i* are ( "s int]e/4 ,9 all su* in/ances x is v necess>y to note ! conditions :i* h obta9$ dur+ ! process ( wa/+1 z )\t ?is1 mislead+ conclusions may be drawn4 ,! in=mation giv5 relates 9 all cases to wr\ght iron1 unless o!rwise /at$4 ,a plate-gird] bridge1 hav+ gird]s "u rails1 0 f\nd to be badly ru/$4 ,! atmosph]ic conditions 7 unusually try+1 ! air be+ damp & impregnat$ ) acid fumes f adjac5t /eel works4 ,t ! wa/+ 0 l>gely due to ?is latt] cause 0 indicat$ by ! fact t ! gird]s ne>e/ to ! /eel works suff]$ m ?an ^? f>!r remov$ & p>tly %elt]$ f ! corrosive influ5ce4 ,! webs 7 9 places eat5 "r ?r\gh1 hav+ lo/ a mean am\nt ( ab\t #a_/h in* full on ea* surface 9 tw5ty-eight ye>s4 ,pa9t+ _h n be5 well att5d$ to4 ,9 a simil> bridge1 n a great di/ance f ?is1 b suffici5tly f> away to modify ! conditions = ! bett]1 consid]able wa/+ 0 also obs]v$1 b m p>ticul>ly :]e ! gird]s _h be5 built into masonry1 :i*1 loos5+ ) ! con/ant movem5t ( ! gird]-ends1 _h all[$ moi/ure to collect1 & ru/ to develop1 )\t ! *ance ( repa9t+ ^! surfaces4 ,! am\nt ( wa/e at ! places indicat$ 01 z 9 ! la/ case1 ab\t #a_/h in* on ea* face1 & 9 ! same "t1 o!r p>ts ( ! gird]s hav+ suff]$ less4 ,illu/ration3 ,,fig4 #eh4 ,a ?ird plate-gird] bridge1 ) out] ma9 gird]s1 cross-gird]s1 & plat$ floor1 c>ry+ a road ov] a railway & sid+s1 & :i* 0 kn[n to h be5 neglect$ 9 ! matt] ( pa9t+1 0 v badly ru/$1 bo? z to ! cross-gird]s & floor-plates4 ,! atmosph]e 0 some:at damp2 ! *ief cause ( det]ioration 01 h[ev]1 ! smoke & /eam f locomotives1 :i* frequ5tly /ood = "s "t1 dur+ %unt+ op]ations1 directly "u ! bridge4 ,! webs ( ! cross-gird]s1 :i* 7 orig9ally #a_/d in* ?ick1 _h ru/$ into occasional holes dur+ f\rte5 ye>s--i4e4 #a_/h in* f ea* surface 9 t "t4 ,:5 remov$ a little lat] ! wa/+ 0 s complete t x 0 possible to knock out ) a light hamm] ! rema9s ( ! web betwe5 flanges & /iff5]s1 s z to leave an op5 frame only4 ,"o ( ! cross-gird]s 0 s treat$ by ! m5 engag$ ^u ! "w1 :5 x pres5t$ ! appe>ance %[n 9 ,fig4 #eh4 ,9 ano!r case--t ( a bridge ) lattice gird]s "u rails--! ends 7 built into masonry1 :i* _h1 ( c\rse1 loos5$1 ) ! usual result4 ,! air ( ! locality 0 c]ta9ly pure1 b some:at damp4 ,! g5]al condition ( ! ironwork 0 good1 b end-b>s ( ! diagonal brac+1 :]e !y _h be5 clos$ 91 _h lo/ #a_/h in* on ea* surface 9 ?irty-?ree ye>s4 ,! top flanges imm$iately "u ! timb] floor 7 9 a v fair /ate1 :i* is ( "s int]e/ :5 x is consid]$ t ^! 7 made ( /eel ( ! same k9d z t already notic$ z be+ us$ 9 ! con/ruction ( small gird]s 7see ,fig4 #df1 ante71 describ$ 9 ! *apt] ^u 8,high ,/ress10 bo? cases dat+ f ! ye> #ahfa4 ,! pa9t+ ^u ! lattice-gird] bridge _h be5 pretty well att5d$ to2 b 9 ! case ( ! small /eel gird]s x _h be5 greatly--p]haps altoge!r--neglect$2 ?is1 c\pl$ ) adv]se atmosph]ic conditions1 _h produc$ ! result t ! rate ( ru/+ _h = ! small gird]s be5 mu* great] ?an t ( ! /eel top flange ref]r$ to1 be+ fully #a_/h in* on ea* surface1 z aga9/ a negligible am\nt "u ! m fav\rable circum/ances4 ,gird]-"w ov] sea-wat]1 z 9 pi]s1 seems to ru/ at a s5sibly great] rate ?an inl& "w "u av]age conditions2 b x is h>dly practicable to make any /rict comp>ison1 z 9 ei!r case ! rate ( oxidation is s mu* affect$--ev5 controll$--by ! c>e be/[$ ^u ! /ructures4 ,?is g5]al conclusion is bas$ ^u ! results ( exam9ation ( wr\ght-iron gird]-"w ov] sea-wat] ( ages v>y+ f f\rte5 to =ty-f\r ye>s4 ,x %\ld be rem>k$1 h[ev]1 t 9 "o case /eel gird]s b five ye>s old1 & :i* 7 frequ5tly wett$ ) sea-spray1 7 f\nd to be wa/+ r badly--! pa9t refus+ to keep ^u ! surface4 ,x may be conclud$ f ! above in/ances1 & f o!rs :i* h come "u notice1 t wr\ght-iron "w1 if n prop]ly c>$ = 9 respect to pa9t+1 or "u conditions o!rwise bad1 may be expect$ to ru/ at a rate :i* corresponds to ! loss ( #a_/h in* on ea* surface 9 f fifte5 to ?irty ye>s2 b ) prop] c>e z to pa9t+1 & exclusive ( exceptionally bad conditions1 x does n appe> to wa/e at any measurable rate4 ,9 "s in/ances1 ^u scrap+ ! pa9t f gird]s :i* _h be5 9 use = ?irty ye>s1 ! au?or has f\nd1 b5ea? ! orig9al r$ lead1 ! metallic surface bright & clean1 %[+ no trace ( ru/4 ,( ord9>y /eelwork ! same _c be said1 ! common exp]i5ce be+ t mild /eel is v liable to be attack$ by ru/4 ,) passable c>e 9 ! bridge-y>d dur+ manufacture1 su* t ) wr\ght iron no aft]-tr\ble w\ld be noticeable1 /eel is v liable to %[1 )9 a ye> ( be+ built up1 num]\s little bli/]s on ! pa9t$ surface2 any "o ( ^! be+ brok5 away discloses a small ru/-pit4 ,?is is m (t5 se5 on ! flange surfaces 7horizontal7 ?an on web surfaces 7v]tical71 b x is probable ! position has little to d ) ! matt]1 & t x is r due to ! fact t ru/ has be5 e>li] />t$ on ! flange-plates1 ^u be+ put ?r\gh ! drill+-ma*9es & inundat$ ) slurry1 :i* occurs only to a m limit$ ext5t ) webs hav+ few] holes4 ,! heads ( /eel rivets d n %[ ?is t5d5cy to 8pit10 or to e>ly developm5t ( ru/4 ,! rivet+ is ab\t ! la/ op]ation 9 mak+ a gird]1 ea* rivet be+ fre$ ( all ru/ by heat+1 & quickly com+ "u ! protection ( oil or pa9t4 ,x may happ5 9 ?is way t ! heads ( rivets on a gird] may be expos$ )\t protection = z _m h\rs only z ! re/ ( ! "w = weeks1 :i* fully acc\nts = ! diff]5ce 9 behavi\r4 ,! ess5tial po9t to be obs]v$ 9 all /eelwork is to prev5t1 if possible1 ! fir/ developm5t ( ru/1 = once begun x is mu* m difficult to arre/ ?an 9 iron2 = ?is reason1 oil+ ( all mat]ial = a /eel bridge1 at a v e>ly /age ( its exi/5ce1 _c be too /rongly insi/$ ^u4 ,?is practice1 h[ev]1 makes ! "w s objectionable1 & ev5 dang]\s :5 be+ lift$--because ( ! liability to slip--to ! m5 engag$ ^u x1 t x is commonly v difficult to ensure x be+ done suffici5tly soon to satisfy a c>eful inspector4 ,if ! "w is c>ri$ out "u cov]1 ! requirem5t is less urg5t4 ,/rictly1 all mat]ial %\ld be oil$ s soon z roll$1 b ! au?or does n rememb] to h se5 ?is done at any ( ! mills he has visit$1 ?\gh x is common en\gh to f9d x specifi$4 ,ironwork does n ne$ ! extreme c>e :i* %\ld be be/[$ ^u /eelwork1 b x is desirable t x %\ld be pa9t$ z soon z possible1 ! surfaces be+ fir/ ?or\ghly clean$4 ,!re is1 probably1 = pa9t+ gird] "w no?+ to beat good r$ lead z a protective coat+2 b !re is consid]able difficulty 9 gett+ x reasonably pure1 )\t :i* quality its utility w be greatly r$uc$4 ,! "q ( purity w1 h[ev]1 be f\nd to be l>gely a "q ( price4 ,x may be /at$ broadly t1 :e!r = /eel or = iron1 ! fir/ protective cov]+ is1 p]haps1 ! mo/ important ( any x w ev] receive4 ,9 repa9t+ old "w1 c>e %\ld be tak5 to remove all traces ( ru/ previ\s to lay+ on ! new coat4 ,x is n an altoge!r uncommon practice to repa9t old /ructures by deal+ only ) ! p>ts readily accessible1 :i*1 be+ less liable to ru/1 probably b little ne$ x2 leav+ ^? p>ts :i* are difficult ( access1 & :]e ru/ is develop+1 unt\*$2 treat+ ! :ole bus9ess z a matt] ( appe>ance simply4 ,?is1 x ne$ h>dly be said1 is indef5sible4 ,x is bett] r to neglect ! surfaces freely expos$ & v5tilat$1 & devote ! :ole c>e ^u ^? o!r p>ts1 conf9$ & difficult to get at2 tak+ ! tr\ble necess>y to remove balla/1 timb]1 or :atev] may ob/ruct ! op]ation1 9 ord] t ! bad places may be ?or\ghly scrap$1 & !n pa9t$4 ,^? p>ts :i* mo/ ne$ att5tion may co/1 p]haps1 to rea*--& deal ) :5 expos$--t5 times z mu* p] y>d ( surface z ! re/ ( ! sup]fices1 :i* ne$s little1 & is always accessible2 b ! co/ %\ld n det] ! prop] c>ry+ out ( ! "w1 z x w prove ! v wor/ sort ( economy to deal ) pa9t+ 9 a p]functory mann]4 ,x %\ld be not$ t gird] "w1 :e!r ( wr\ght or ca/ iron1 :5 emb$d$ 9 lime or cem5t concrete1 or mort>1 g5]ally proves to be v well pres]v$1 provid$ t close contact has obta9$4 ,ca/-iron gird]s1 :5 c>ry+ jack ar*es re/+ ^u ! bottom flanges1 are f\nd aft] long use to be 9 rem>kably good ord]1 :5 f9ally tak5 out1 hav+1 inde$1 ! surface appe>ance ( new gird]s4 ,mu* ! same rem>ks apply to gird]s ( wr\ght iron c>ry+ jack ar*es1 :]e protect$ by ! brickwork2 provid$ t ! gird]s are suffici5tly /iff to m9imise deflection1 & all[ ! masonry or brickwork to adh]e to ! surfaces4 ,su* gird]s are 9 a v diff]5t condition to ^? previ\sly ref]r$ to1 9 :i* ! ends ( ! gird]s1 c>ry+ a light floor /ructure1 are built into masonry :]e ! deflection slope is greate/2 ?\gh1 ap>t f ! few cases :]e adh]5ce c be reli$ ^u1 build+-9 is an undesirable practice1 & has ! disadvantage t aft]-exam9ation is only possible by remov+ portions ( ! masonry1 :i* x is evid5t w\ld v seldom be resort$ to4 ,ca/ iron has ord9>ily--unlike wr\ght iron or /eel--great capacity = resi/+ ru/1 & w1 aft] _m ye>s ( absolute neglect1 appe> b little ! worse2 an advantage :i* is ! m pron\nc$ :5 consid]$ relatively to ! great] ?ickness ( ! ?9ne/ p>ts 9 ca/-iron gird]s1 ! p]c5tage ( wa/e be+ proportionately less5$4 ,ca/ iron does1 h[ev]1 behave some:at badly 9 sea-wat]1 ! metal sometimes los+ its orig9al "*1 & becom+ 9 "t q s(t2 ?\gh1 if n worn away1 z by ! attrition ( %+le1 ma9ta9+ its orig9al bulk4 ,( "s =ty-five ca/-iron piles belong+ to v>i\s /ructures1 exam9$ :il/ engag$ ^u sea-pi] "w = ,mr4 ,/4 ,george-,moore1 ?\gh ! au?or f\nd some:at div]se results1 9 no case did !re appe> to be any g5]al s(t5+ ( ! :ole ?ickness1 b a di/9ct *ange = "s def9ite di/ance inw>ds1 g5]ally to be decid$ )\t difficulty1 beyond :i* ! metal appe>$ to reta9 its orig9al "*4 ,9 all cases any mat]ial dep? ( s(t5+ 0 f\nd close to ! gr\nd1 ?is dep? rapidly decreas+ high] up1 till1 at a height ( #e feet1 b little if any s(t5+ c\ld be detect$4 ,at #b feet above gr\nd ! s(t5+ 0 frequ5tly b "o-qu>t] ( t at gr\nd level4 ,!re 01 too1 (t5 a consid]able diff]5ce 9 ! behavi\r ( diff]5t piles 9 ! same /ructure "u simil> conditions2 "o pile be+ f\nd to h only "o-f\r? "p ( ! s(t5+ notic$ 9 o!rs1 or possibly none at all4 ,= six diff]5t /ructures ! am\nt ( s(t5+ ne> gr\nd level1 ( ab\t tw5ty-five piles exam9$1 0 z giv5 9 ! table on ! next page4 ,! greate/ dep? ( s(t5+ f\nd 7see ,no4 #b7 0 #i_/af in*1 #a foot above gr\nd1 9 a pile ?irty-six ye>s old4 ,! decay$ mat]ial :5 remov$ 0 ( a s(t1 greasy consi/5cy1 p]fectly black1 :i* a few h\rs lat] 0 f\nd to h *ang$ to a dry yell[ p[d]1 by ! rapid absorption1 x may be suppos$1 ( atmosph]ic oxyg54 ,x is app>5t1 !re=e1 f ?is example t det]ioration may proce$ to a consid]able dep?2 b x %\ld be obs]v$ t o!r piles ( ! set %[$ s(t5+ at gr\nd level ( #a_/h in* only4 ,,s(t5+ ,,( ,,ca/-,,iron ,,piles ,,9 ,,sea-,,wat]4 ---------------------------------------- -------------------- ,no4 ,age4 ,maximum ,maximum ,mean ,rate ,quality ,mat]ials ,s(t5+4 ,rate ( ( ( ,metal4,ent]$ ,s(t5+4 ,s(t5+4 by ,piles4 ---------------------------------------- -------------------- #a #ag ye>s#e_/af 94 #a_/h 94 9 #a_/h 94 9,s(t ,extremely #g ye>s #ae ye>s s(t s&/one4 #b #cf ye>s#i_/af #a_/h 94 9 ,no result ,rubble #h-a_/b ye>s m\nd4 #c #cb ye>s#c_/h #a_/h 94 9 #a_/h 94 9,mod]ate-,f9e #aa ye>s #ae ye>s ly h>d s&4 #d #ch ye>s#a_/aj #a_/h 94 9 #a_/h 94 9,h>d ,extremely #dg ye>s #adj ye>s h>d rock4 #e #ag ye>s,small ,negligible 787 ,s& & ,%+le4 #f #ad ye>s,negligible,ditto 787 ,s&4 ---------------------------------------- --------------------- ,! lea/ rate ( s(t5+ notic$1 ap>t f ^? /ructures ( a m rec5t date1 9 two ( :i* x 0 v slight1 occurr$ 9 a pi] ?irty-eight ye>s old 7,no4 #d71 :]e1 ( ?ree piles te/$1 two 7 q h>d1 & ! ?ird s(t5$ #a_/aj in* only4 ,:atev] may be ! precise cause ( ! *ange1 x does n appe> to be affect$ by ! p]iod or p]c5tage ( imm]sion dur+ ! rise & fall ( tides4 ,illu/ration3 ,,fig4 #ei4 ,?is w be cle> f ! diagram1 ,fig4 #ei1 :i* ref]s to f\r piles 7,no4 #c ( table71 all ( ! same age1 9 ! same /ructure4 ,on ea* pile ! dep? ( s(t5+ is giv5 at po9ts 9 /rict relation to ea* o!r1 & to ! tidal range4 ,! p]c5tages ( imm]sion = ! v>i\s heights are also giv51 f a /udy ( :i* x w be app>5t t ^! h no relation to ! am\nt ( s(t5+2 ?is1 inde$1 is always greate/ ne> ! gr\nd1 at :atev] actual height x may be4 ,= in/ance1 pile ,a 0 at gr\nd-level s(t5$ #a_/d in*1 t po9t be+ #fj p] c5t4 ( its life "u wat]2 b on pile ,b1 at a po9t #gd p] c5t4 ( ! "t subm]g$1 & #d feet above a l[] gr\nd-level1 no s(t5+ 0 app>5t2 fur!r1 at gr\nd-level ( ?is pile1 ! p]c5tage be+ !re #hg1 ! s(t5+ 0 no great] ?an at gr\nd-level at pile ,a4 ,x is probable t :ile ! p]c5tage ( subm]sion 9 mov+ wat] h>dly appe>s to affect ! result1 yet prolong$ contact ) wet s&1 sea-we$1 or cl++ %ell-fi% may d s4 ,?is seems to sugge/ t ! process ( *ange1 z betwe5 ! sea-wat] & ! iron1 is sl[1 & to be effective mu/ be cont9u\s2 s t x is only f\nd to any consid]able ext5t :]e ! wat] 9 contact ) ! surface is /ill4 ,9 ! two wor/ cases1 ,nos4 #a & #b ( ! table1 at po9ts #a foot & #f in*es above gr\nd-level1 ! surface 0 9 "o pile %r\d$ 9 a ?ick mantle ( heavy sea-we$1 & 9 ! o!r cov]$ by molluscs2 9 bo? in/ances ! surfaces be+ ?us kept moi/ & undi/urb$4 ,! piles ( ! f\r? case 7 9 h>d rock1 7 clean1 &1 :]e accessible1 always ei!r 9 mov+ wat] or q dry4 ,h[ev] ?is may be1 ! p[] to resi/ s(t5+ c]ta9ly appe>s to v>y l>gely ) ! quality ( ! iron4 ,! piles1 ref]r$ to above1 9 :i* det]ioration proce$$ at ! mo/ rapid rate 7 c]ta9ly ( a s(t metal1 ! fir/ be+ m>k$ly s4 ,on ! o!r h&1 c]ta9 piles 7,no4 #d7 ( h>d1 close-gra9$ iron suff]$ v little4 ,x may be m5tion$ ) respect to ! la/ nam$1 z a matt] ( int]e/1 t ! caps ( ! l[] l5g?s 7j above gr\nd-level7 _h be5 ca/ ) %ort pieces ( wr\ght iron project+--possibly = lift+ purposes--:i* dur+ ?irty-eight ye>s _h alt]$ 9 "* to some?+ v l s(t5$ ca/ iron1 b lam9at$1 & h>d]4 ,( ab\t #a-a_/d in* orig9al ?ickness1 only #c_/af in* rema9$ hav+ ! semblance ( wr\ght iron4 ,! p]c5tage ( subm]sion 0 ab\t #fj4 ,a numb] ( piles1 n includ$ 9 ! table1 v>y+ f fifte5 to =ty-f\r ye>s old1 & ( ! same /ructure to :i* set ,no4 #b belong$1 7 all f\nd to be h>d1 ) ! exception ( "o %[+ #c_/af in* ( s(t5+4 ,^! are omitt$1 because ! mud surr\nd+ !m 0 at ! "t ( exam9ation unusually high1 s t ! m normal gr\nd-level c\ld n be rea*$1 at :i* po9ts te/+ might h disclos$ diff]5t results4 ,x is probable t = any piles /&+ 9 s(t mat]ial exam9ation bel[ ! surface w\ld reveal m pron\nc$ s(t5+ ?an :]e occasionally expos$4 ,to meet ! effects ( sea-wat] on ca/-iron piles1 & = o!r reasons1 x is a common & good practice to make ! l[] l5g?s ( great] ?ickness--say1 #c_/h in* m--?an t suffici5t = ! upp]4 ,occasionally1 also1 ! bottom l5g?s are fill$ ) concrete1 :i* no d\bt adds to ! l5g? ( "t dur+ :i* !y may be reli$ ^u4 ,,*apt] ,x4 ,,exam9ation1 ,,repair1 ,,& ,,/r5g!n+ ,,( ,,rivet$ ,,bridges4 ,9 ! prec$+ *apt]s defects ( v>i\s k9ds to :i* rivet$ bridgework is liable h be5 m p>ticul>ly dealt )2 x is n[ propos$ to consid] ! exam9ation ( su* /ructures1 foll[+ ?is by a ref]5ce to me?ods ( repair & /r5g!n+1 leav+ ! treatm5t ( o!r classes ( bridgework to be develop$ "u _! prop] head+s1 ?\gh "s ( ! rem>ks imm$iately foll[+ w apply to all4 ,! exhau/ive survey ( a bridge is only to be made aft] consid]able exp]i5ce 9 ! "w1 b x may be /at$ t 9 look+ = defects x is well to seek :]e !y are lea/ expect$1 till1 ) practice1 "o kn[s bett] :]e to direct att5tion4 ,:5 exam9+ ) a view to pron\nc+ an op9ion ^u ! fitness ( ! /ructure to rema9 9 place1 if 9 any real d\bt1 x is wise to give a ca/+ vote aga9/ x2 & f9ally x may be said t ^u tak+ d[n a bridge condemn$ = any "o or m defects1 x %\ld be exam9$ = worse4 ,?is may seem to be some:at pessimi/ic1 b is bas$ ^u ! tea*+s ( exp]i5ce4 ,prelim9>y exam9ation ( a bridge may reveal su* faults or weaknesses z at once to ensure its condemnation2 b if ?is is n ! case1 & !re is a reasonable probability t ! /ructure may be giv5 a fre% lease ( life1 x w1 = ! purpose ( e/imat+ ! /r5g?1 or = possible repairs1 commonly be desirable to secure precise p>ticul>s ( ! exi/+ /ructure indep5d5tly ( any draw+s t may be 9 exi/5ce1 & :i* w v probably be incorrect1 ! f9i%$ "w1 if old1 seldom agree+ ) ! contract draw+s4 ,a f9al decision may 9 ?is case be def]r$ till aft] ! measur+ up has be5 complet$1 ! condition ( ! /ructure becom+ m famili> 9 ! process4 ,x is desirable fir/ to asc]ta9 :e!r ! bridge rema9s 9 good =m1 :e!r ! camb] ( gird]s appe>s to be :at might be expect$1 or agreeable ) exi/+ records1 ?\gh mu* reliance mu/ n be plac$ ^u figur$ camb]s1 x be+ q common = gird]s to leave ! bridge y>ds ) ! camb] some?+ o!r ?an t int5d$4 ,! deflections "u live load w also be obs]v$1 & comp>$ ) ! calculat$ result1 or *eck$ by judgm5t4 ,! calculations ^u :i* /r5g? & deflections are bas$ w1 ( c\rse1 ref] to ! actual sections1 :i* are sometimes a little difficult to asc]ta9 if !re has be5 irregul> ru/+4 ,9 cont9u\s gird]s also1 levels hav+ be5 tak51 all[ance %\ld be made = effects ( settlem5t1 if any2 & ) ar*es evid5ce ( movem5t ( ! pi]s or abutm5ts s\ght =1 ) ! l object4 ,x is seldom t ! ma9 flanges ( gird]s %[ signs ( weakness1 unless f flexure 9 ! case ( long & n>r[ top memb]s1 insuffici5tly /iff5$2 b !re may be want ( tru? f o!r causes already dealt )4 ,9 plate gird]s ! webs %\ld be mo/ c>efully scann$ = possible cracks1 p>ticul>ly :]e cross-gird]s are connect$1 & along ! upp] edges ( bottom flange angles1 if ! floor re/ ^u ! flange4 ,all rivet$ connections1 ( c\rse1 ne$ close att5tion1 bo? = /ra9+ effects1 :]e !re is a liability to wrack+1 & to detect loose rivets4 ,loose rivets & want ( tightness 9 o!r p>ts ( ! "w may frequ5tly be detect$ at sight by a r$di% bloom :i* appe>s on ! neighb\r+ surfaces1 caus$ by ru/ work+ out & spread+ "u ! effects ( wea!r2 x may be se5 r\nd rivet-heads or along ! edges ( angle-b>s1 or o!r p>ts :]e !re is movem5t4 ,loose rivets1 ?\gh g5]ally to be detect$ also by ! hamm]1 may p]haps 9 ! case ( ?9-webb$ cross-gird]s be work+ 9 ! web-?ickness only1 possibly to a consid]able ext5t4 ,?is1 if n o!rwise evid5t1 may sometimes be detect$ by simultane\s deflection te/s--) rods--at ! top & bottom flanges ( a gird]1 at ! same di/ance f ! be>+s4 ,any diff]5ce 9 ! read+s may indicate loose web-rivets1 or possibly a te> 9 ! web runn+ p>allel to ! flange angles4 ,brac+s betwe5 gird]s are v apt to display a ri* h>ve/ ( work+ rivets4 ,cross-gird]s & longitud9als also may h loose rivets at _! connections1 & be v badly wa/$1 ) q possibly cracks 9 ! webs1 or o!r defects already enl>g$ ^u4 ,! condition ( ! road ^u ! bridge w frequ5tly be an indication ( ! /ate ( ! floor :i* c>ries x2 or ! exi/5ce ( rail-jo9ts :i* are work+ badly may v prop]ly lead to a critical exam9ation ( ! gird]-"w imm$iately bel[1 z ?is is a fruitful s\rce ( damage 9 light con/ructions4 ,floor-plates1 :]e ^! exi/1 %\ld be scann$ = leakages1 dra9age nozzles1 & gutt]+1 to see t !y are free1 ! atta*m5ts ( ! latt] be+ (t5 loose & unsatisfactory4 ,tr\gh floors may be expect$ to %[ loose rivets ne> ! ends1 ) a probability ( excessive leakage :]e !y abut aga9/ ! webs ( support+ gird]s4 ,floor plates re/+ ^u abutm5ts or pi]s1 be+ v liable to s]i\s decay1 require att5tion1 & gird]-"w ent]+ masonry %\ld receive close scrut9y1 any ob/ruction to a suffici5t exam9ation be+ remov$ s f> z is judg$ suffici5t = ! purpose4 ,! /ructure %\ld1 ( c\rse1 be closely wat*$ dur+ ! passage ( live load = any signs ( abnormal movem5t1 excessive vibration1 or lur*+4 ,9 addition to seek+ = ^! v>i\s defects1 or o!rs :i* h be5 ref]r$ to 9 ^! pages at l5g?1 x w be well always to be alive to ! possibility ( faults to be se5 = ! fir/ "t1 or ( :i* ! au?or has furni%$ no in/ance4 ,hav+ =m$ a reliable op9ion z to ! /ate ( ! bridge1 ?is1 if satisfactory1 may leave to be det]m9$ only ! "q ( /r5g? relative to ! loads c>ri$4 ,x is app>5t t /ress limits suitable = a new /ructure1 :i* has all its life be=e x1 ( purpose mod]ate to cov] possible det]iorations1 ! gr[? ( loads1 & o!r adv]se influ5ces1 may to avoid imm$iate recon/ruction1 reasonably be p]mitt$ ( a high] value = a fur!r t]m ( ye>s 9 ! case ( a /ructure :i* x is kn[n has = a consid]able p]iod behav$ well1 & rema9s 9 good condition4 ,:at ?is high] value may be w be greatly influ5c$ by ! circum/ances ( ea* case1 &1 be+ l>gely a matt] ( judgm5t1 may be expect$ to v>y ) diff]5t eng9e]s4 ,exp]i5ce %[s1 h[ev]1 t ! nom9al unit /ress 9 an old bridge may be a v consid]able am\nt 9 excess ( t all[$ = new "w1 )\t1 ( necessity1 %[+ any ill effects2 & ! au?or is ( op9ion t = old bridges 9 good condition x is q prud5t to all[ an excess ( #cc p] c5t4 beyond t p]missible = a new design4 ,if ! /ructure is too weak to satisfy ?is modifi$ condition1 x may be possible to br+ x )9 ! /ress limit by a r$uction ( balla/ or o!r removable dead weight4 ,if ?is exp$i5t does n promise to be satisfactory1 or ! bridge %[s actual signs ( weakness1 or palpable defects1 x w be necess>y to deal ) ! "q ( repair1 /r5g!n+1 or recon/ruction4 ,! repair ( built up bridgework resolves itself l>gely into a matt] ( replac+ loose rivets by cutt+ ^! out1 rhym]+ ! holes1 if desirable1 & aga9 rivet+4 ,x w (t5 be suffici5t to d ?is ) no p>ticul> precautions z to bolt+ up tempor>ily2 ! rivets hav+ be5 loose1 may v well be sp>$ = a "t4 ,9 re-rivet+ cross-gird] connections x may1 h[ev]1 be imp]ative to remove all ! rivets1 bolt+ up securely z ?is is done1 9 ord] to make a tight job1 tak+ out ea* bolt 9 turn z requir$1 & aga9 fill+ ! holes2 or x may be well 9 a bad case fir/ to remove all loose rivets1 sub/itut+ good bolts1 9 ord] t "w :i* has gone out ( %ape ow+ to defective rivets may fir/ be br\ght true4 ,cross-gird] webs1 crack$ v]tically or ne>ly s1 are commonly repair$ ) splice-plates on ei!r side2 b 9 do+ ?is x is undesirable to add plates ( excessive ?ickness relative to ! web--probably poor--z by an abrupt *ange ( web section x appe>s n unlikely a fre% break may be fav\r$4 ,illu/ration3 ,,fig4 #fj4 ,illu/ration3 ,,fig4 #fa4 ,illu/ration3 ,,fig4 #fb4 ,illu/ration3 ,,fig4 #fc4 ,replac+ wa/$ flange-plates1 or add+ new plates to ^? :i* exi/1 is occasionally resort$ to 9 ! case ( ma9 gird]s1 ! flanges ( :i* are suffici5tly accessible1 b ! op]ation is difficult1 takes "s little "t1 & %\ld only be attempt$ "u ! con/ant sup]vision ( a ?or\ghly capable man4 ,:5 done1 if ! gird] has n be5 reliev$ ( load by /ag+1 ! /ress "u full load w be unequally di/ribut$ betwe5 ! old & ! new section1 ! old always tak+ m by ! am\nt ( ! dead-load /ress previ\sly c>ri$4 ,! me?od :i* ! au?or has se5 appli$ to lattice gird]s ( ab\t #hj feet span1 hav+ good angle-b>s 9 ! flanges1 ) a %all[ v]tical web = atta*m5t ( diagonals1 consi/$ 9 fir/ cutt+ out ! old flange rivets1 & sub/itut+ bolts well screw$ up1 till all ! rivets necess>y _h be5 remov$4 ,! new plate l5g? hav+ be5 prep>$1 01 on a ,sunday1 dur+ a few h\rs' cessation ( traffic1 m>k$ (f1 ! tempor>y bolts be+ remov$ = ! purpose1 & !n replac$4 ,aft] ! plate _h be5 drill$1 on a lat] ,sunday1 x 0 f9ally put into position1 bolt$ up1 & rivet$ at leisure2 cov]-plates make additional tr\ble1 b are dealt ) on ! same pr9ciple4 ,! me?od z %[n 9 ,fig4 #fj is1 h[ev]1 b>ely practicable = s _m plates4 ,x is pref]able1 if x is propos$ to add section1 to d ?is ) z little int]f]5ce z possible ) exi/+ rivets ( importance4 ,?is may be accompli%$1 if ! exi/+ plates are n too wa/$ at _! edges1 by rivet+ on new /rips or angle-b>s 7see ,figs4 #fa to #fc74 ,occasionally ! /r5g? ( a gird] is increas$ by ! addition to ! top or bottom boom ( mat]ial 9 su* a =m z s5sibly to increase ! dep?1 & ?us1 :ile add+ increas$ section to "o boom1 to r$uce ! /ress 9 ea*1 ?\gh to dissimil> am\nts4 ,by ?is device also ! relief is effective only z reg>ds ! live-load /ress2 "u dead load only ! new mat]ial does no "w1 provid$1 ( c\rse1 t no relief /ag+ 0 us$ dur+ ! alt]ations4 ,= gird]s c>ry+ any consid]able proportion ( dead load ! me?od is v ineffici5t1 ?\gh = o!rs1 9 :i* ! live load is relatively l>ge1 ! result %\ld be m satisfactory4 ,z ?is "q ( add+ new section to old is ( mu* importance 9 deal+ ) repairs & /r5g!n+ op]ations1 a few g5]al rem>ks ^u ! subject w be p]t95t4 ,! difficulty 9 su* "w commonly is to cause ! new to r5d] any consid]able assi/ance to ! old 9 ^? cases :i* occur 9 practice4 ,if a b> be imag9$ "u longitud9al /ress v>y+ betwe5 #j & a maximum1 !n1 if ! area ( ! piece be increas$ at ! "t :5 x takes no /ress1 its capacity = resi/+ ! maximum am\nt w be increas$1 & = add$ mat]ial ( simil> ela/icity ! unit /ress proportionately r$uc$4 ,if1 h[ev]1 ! load on ! b> does n v>y1 ! m]e addition ( metal w n relieve ! orig9al section 9 any degree4 ,to take a ?ird case1 ( ! maximum be+ twice ! m9imum load1 x w be necess>y1 9 ord] to l[] ! maximum unit /ress by #be p] c5t41 to d\ble ! orig9al section ( ! b> if1 z suppos$1 ! extra metal has be5 add$ to ! piece :5 "u ! small] load1 s t ! new section is only effective 9 assi/+ to c>ry ! rema9d] ( ! load at su* times z x may be impos$4 ,! relation%ip /&s ?us3-- ,live load ,new area ---------------- -------------- relief4 ,live dead load ,new old area ,^! /atem5ts w be true "u ! conditions nam$1 )9 ! ela/ic limit ( ! mat]ial2 b "s advantage w\ld be d]iv$ 9 ! second case1 & a m m>k$ b5efit 9 ! ?ird1 if ! load assum$ to be a maximum 7 exce$$1 or if ! composite b> 7 te/$ to de/ruction2 z1 h[ev]1 ^! effects w\ld be outside ! limit+ conditions impos$1 x mu/ be a matt] ( judgm5t z to h[ f> ?is res]ve ( /r5g? may be consid]$ ( value4 ,if1 in/ead ( simply add+ section to ! b>1 "s "p ( ! con/ant load is put ^u ! new section by ! mann] ( atta*m5t1 ! comb9ation w1 ( c\rse1 be m effective4 ,to apply ^! consid]ations & illu/rate ! way 9 :i* ! two me?ods ( add+ flange section "w out :5 r$uc$ to figures1 ! case w be suppos$ ( a gird] #f feet deep1 c>ry+ a load ( :i* "o-?ird is dead & two-?irds live4 ,to ! flanges ( ?is gird] are add$ plates equal to #ej p] c5t4 ( ! orig9al areas1 9 ord] to r$uce ! /ress ( #g tons p] squ>e in* to :i* ! gird] be=e /r5g!n+ is liable1 ! dep? rema9+ sub/antially unalt]$4 ,) dead load only ! orig9al section w\ld be /ress$ to #bc tons p] squ>e in*1 ! new section be+ !n un/ress$4 ,"u full load ! new & old mat]ial take #ca tons p] squ>e in* additional1 mak+ ! modifi$ /ress on ! orig9al section #ed tons p] squ>e in*1 z aga9/ #g tons2 or a r$uction ( #bb p] c5t4 ,?is comp>es ) #cc p] c5t41 ! relief due to #ej p] c5t4 increase ( flange area "u ord9>y conditions ( /ress di/ribution4 ,let ! second me?od ( /r5g!n+ ! gird] n[ be consid]$1 us+1 = purposes ( comp>ison1 ! same total am\nt ( new mat]ial to increase ! gird] dep? by an addition to ! top flange4 ,?is section w be equal to ! area ( "o flange1 :i*1 ?\gh x may be appli$ 9 _m diff]5t ways1 giv+ a great] or a less increase to ! dep?1 w\ld probably be us$ 9 "s su* mann] z t %[n 9 ,fig4 #fd1 increas+ ! effective dep? = live-load /ress by ne>ly #aj in*es4 ,illu/ration3 ,,fig4 #fd4 ,! add$ mat]ial w1 z 9 ! previ\s case1 leave ! dead-load /ress unalt]$1 or #bc tons p] squ>e in*4 ,! /ress 9 ! bottom flange due to live load w1 h[ev]1 n[ be #da tons p] squ>e in*1 mak+ a total /ress ( #fd tons p] squ>e in*1 aga9/ #g tons--! orig9al /ress4 ,! r$uction "h is #h p] c5t4 only1 z comp>$ ) #ab p] c5t41 ! relief due1 "u ord9>y conditions1 to an increase ( effective dep? f #f feet to #f feet #aj in*es1 & by ! use ( additional mat]ial1 equal1 z be=e1 to "o-half ( ! total flange areas be=e ! alt]ation4 ,! effect on ! top flange ne$ n be "h gone into 9 detail1 b x may be said t1 ow+ to ! increase ( gross section & ( dep?1 ! ultimate /resses ( bo? ! new & old mat]ial are greatly less ?an z giv5 = ! bottom flange4 ,gird]s /r5g!n$ by ! fir/ ( ^! two me?ods w\ld1 x is probable1 if te/$ to de/ruction1 give results m ne>ly 9 accord ) ! actual p]c5tage increase ( flange section1 pla/ic de=mation ( ! metal1 be=e failure1 t5d+ to r$uce ! diff]5ces ( /ress on ! new & old mat]ial ( ! sections4 ,illu/ration3 ,,figs4 #fe & #ff4 ,web memb]s ( lattice gird]s may1 if weak1 sometimes be dealt ) by ! introduction ( supplem5t>y b>s1 p>allel to & betwe5 ! old memb]s1 or by ! addition ( /rips or angles to ! exi/+ diagonals4 ,! treatm5t w be l>gely influ5c$ by ! nature ( ! old detail1 :i* may l5d itself to "s "o arrangem5t mu* bett] ?an to any o!r4 ,end rivet+ ( web memb]s may1 if x has become loose1 be dealt ) by simply rhym]+ ! holes a size l>g]1 & re-rivet+ 9 ! be/ mann]1 if ! /resses are n excessive2 or x may be necess>y to devise "s additional atta*m5ts by :i* new rivets are br\ght into use 7see ,figs4 #fe & #ff74 ,! effective relief due to supplem5t>y rivets w be influ5c$ by simil> consid]ations to ^? gov]n+ increase ( section4 ,illu/ration3 ,,fig4 #fg4 ,illu/ration3 ,,fig4 #fh4 ,old /ructures are v frequ5tly defici5t 9 brac+1 :i* may1 9 su* cases1 be advantage\sly introduc$2 or gird]s individually weak may be r5d]$ collectively effici5t by suitable brac+4 ,9 consid]+ ! advisability ( ?is1 h[ev]1 ! case %\ld be view$ ) reg>d to ! possible effects ( su* memb]s1 z already dealt ) 9 ! *apt] relat+ to ^! que/ions4 ,!re x has be5 po9t$ out t brac+ betwe5 a sy/em ( p>allel gird]s may h ! effect1 "u live load1 ( increas+ ! /ress on ! out] gird]s due to twi/+ ( ! /ructure z a :ole1 ?\gh ! inn] gird]s w1 except = full load+ ( ! :ole bridge1 be advantag$ z to /ress values1 & 9 any ev5t bett]$ by be+ held up to _! "w4 ,! effect ^u ! out] gird]s may be met by increas+ _! /r5g?1 if ?is appe>s to be necess>y4 ,9 all su* alt]ations ! detail %\ld be s*em$ ) special c>e to ensure simplicity 9 execution1 smi?'s "w be+ rigor\sly avoid$4 ,a good arrangem5t = supplem5t>y brac+ betwe5 plate-gird]s1 :i* gives little tr\ble 9 c>ry+ out1 is %[n 9 ,fig4 #fg2 or :]e ! /iff5]s ( su* gird]s are 9 l9e across ! bridge1 ! detail giv5 9 ,fig4 #fh may involve less exp5diture4 ,difficulties may be exp]i5c$ 9 rivet+1 unless great c>e is tak5 9 ! position+ ( rivets4 ,fitt+-bolts are only to be reli$ ^u z su*1 if !y really ju/ify ! "n2 !y are1 ?\gh easy to specify1 by no means easy to secure "u ! conditions ( practical "w4 ,weak cross-gird]s may make alt]ations--9 "s cases consid]able--necess>y1 to rectify ! defect ( /r5g?4 ,! removal ( old gird]s to make room = new is seldom resort$ to1 unless ! exi/+ detail r5d]s ?is a simple op]ation2 b x is n unusual to introduce new gird]s betwe5 ! old 9 cases :]e !re is no plat$ floor to make ! "w difficult4 ,by ?is me?od !re is1 ( c\rse1 an increase ( appreciable am\nt 9 ! dead load c>ri$ by ! ma9 gird]s1 :i* w\ld 9 _m in/ances be objectionable4 ,) deep & heavy ma9 gird]s1 hav+ plate webs1 cross-gird]s may be /r5g!n$ by improv+ ! end connections by suitable gussets1 & atta*m5t to good v]tical /iff5]s1 ! fixity ( ! ends ?us aim$ at be+ assur$ by ov]head /ruts or gird]s1 f "o ma9 gird] to its fell[1 at int]vals ap>t well consid]$ ) ref]5ce to ! horizontal /r5g? ( ! top flanges1 ! :ole ?us mak+ a clos$ frame1 z %[n 9 ,fig4 #fi4 ,! me?od appe>s feasible1 b x %\ld be /at$ t ! au?or has n kn[n x to be appli$ 9 its entirety z a means ( /r5g!n+ an old floor4 ,illu/ration3 ,,fig4 #fi4 ,a simple & v common device consi/s 9 sub/itut+ = ! ord9>y cross-sleep] road1 :]e ?is exi/s1 /\t timb] longitud9als "u ! rails1 :i* h1 :]e ! cross-gird]s d n exce$ #e feet c5tres1 a m>k$ di/ributive effect1 t5d+ to r$uce ! maximum load ^u any individual gird]4 ,) a simil> object1 tr\gh gird]s conta9+ longitud9al timb]s are sometimes adopt$ :]e ! dep? available is n en\gh to enable suffici5tly /iff timb]s to be us$ alone4 ,9 ei!r case ! object s\ght is ! same--to modify ! effect ( ! heavi] :eel loads ^u isolat$ cross-gird]s4 ,:5 ! spac+ is s close z #d feet1 ! b5eficial result ( ?is treatm5t is consid]able1 b at #h feet c5tres x c h b a mod]ate effect :]e timb]s alone are us$4 ,occasionally1 = long cross-gird]s1 a di/ribut+ gird] is plac$1 ) ! same int5t1 9 ! #f feet way1 its function be+ limit$ to ?is use only if ! dep? & /r5g? are suffici5tly small to s]ve ?is object alone1 z di/9ct f ! case 9 :i* x becomes a c>ry+ gird] transf]r+ load to ! abutm5ts4 ,z a di/ributor simply1 ! gird] has to equalise ! b5d+ mom5ts among/ ! cross-gird]s1 to effect :i* x w be evid5t t ^! mom5ts hav+ be5 asc]ta9$ = ! sev]al cross-gird]s previ\s to alt]ation1 = a position ( ! :eel loads su* t ! heavie/ comes ^u a c5tre cross-gird]1 ! mean ( ^! mom5ts w1 :5 comp>$ ) t = ea* gird]1 %[ ! diff]5ce to be induc$ z a result ( introduc+ ! di/ributor4 ,^! diff]5ces ( mom5t r5d] necess>y at ! c5tre ( ! cross-gird]s reactions upw>ds or d[nw>ds1 z ! case may be1 ( am\nts compet5t to induce mom5ts bel[ ! inn] rails equal to ^! diff]5ces4 ,x is ^! reactions :i* mu/ be provid$ by ! di/ribut+ gird] at a mod]ate /ress1 & )\t flexure ( su* an am\nt z s5sibly to modify ! reactions4 ,! greate/ section necess>y at any "o po9t may !n be adopt$ = ! gird] ?r\gh\t4 ,! result w commonly "w out to a mod]ate section1 b !re w be no h>m 9 a little excess 9 a case ( ?is k9d1 ! total co/ be+ b little affect$ by "s small addition to ! weight1 :]e lab\r ^u ! site is s consid]able an item z 9 "w ( ?is description4 ,! ends ( ! di/ribut+ gird] %\ld be c>ri$ on to ! abutm5ts or pi]s to ensure adequate relief ( ! end cross-gird]s4 ,x w be f\nd desirable 9 arrang+ = di/ribut+ gird]s to asc]ta9 at an e>ly /age1 by bon+ or by levell+1 ! condition ( ! cross-gird]s z to uni=mity ( heights1 z ?is may affect ! l5g? mo/ suitable = sep>ate sections4 ,betwe5 ! und]side ( ! di/ributor & ! cross-gird] tops !re w commonly be spaces ( v>y+ am\nts1 :i* %\ld be fill$ by pack+s to fit1 r ?an by pull+ ! "w toge!r by =ce1 introduc+ undesirable /resses ( unc]ta9 am\nt4 ,9 ! e>li] rem>ks ^u ! /r5g!n+ ( bridgework by ! use ( new mat]ial1 x has be5 assum$ t ! modulus ( ela/icity ( ! new metal is simil> to t ( ! old2 x may1 h[ev]1 z 9 cases :]e wr\ght-iron "w is re9=c$ by additions 9 /eel1 be necess>y to take ! diff]5ce ( ela/ic prop]ties into acc\nt1 ) :i* object ! new section %\ld be multipli$ by a quantity 7great] or less ?an unity7 inv]sely proportional to ! high] or l[] modulus ( ! new mat]ial1 t is to say1 by ,e ( old mat]ial ----------------- ,e ( new mat]ial ,,*apt] ,,xi4 ,,/r5g!n+ ,,( ,,rivet$ ,,bridges ,,by ,,c5tre ,,gird]s4 ,! addition ( di/ribut+ gird]s1 describ$ 9 ! la/ *apt]1 z a means ( /r5g!n+ a bridge floor1 :ile suffici5t 9 _m cases s f> z ! cross-gird]s are conc]n$1 does n 9 any appreciable way assi/ ! ma9 gird]s4 ,:5 = a two-l9e bridge1 hav+ out] ma9 gird]s only1 ?is result also is desir$1 toge!r ) a m complete relief ( ! floor /ructure1 c5tre ma9 gird]s may be us$1 plac$ ei!r above or bel[ ! cross-gird]s1 on ! c5tre l9e ( ! bridge4 ,!re are two pr9cipal ways 9 :i* su* a gird] may be br\ght into use2 ! easi]1 b g5]ally less economical1 is by mak+ a simple atta*m5t to ! cross-gird]s1 ! old gird] "w /ill tak+ ! :ole dead load4 ,by ?is me?od ! new gird] does no "w b c>ry itself till ! live load comes ^u ! bridge1 & mu/ be made v /iff to take any s5sible portion ( ! runn+ load2 ! second me?od is to make ! connection adju/able1 s t a "p ( ! floor weights may be impos$ ^u ! new gird] z an initial load4 ,9 do+ ?is ! old out] gird]s w rise slightly1 be+ reliev$ ( /ress1 & ! cross-gird]s also lift$ at ! middle1 :il/ ! new gird] is depress$ z ! load is br\ght ^u x4 ,) "s "p ( ! live load a v consid]able proportion ( ! total may 9 ?is way be c>ri$ by a c5tre gird] ( mod]ate section4 ,! :ole "q1 by ei!r me?od1 turns ^u deflections2 & x is 9 det]m9+ ! relative movem5ts ( ! gird]s t ! problem *iefly lies4 ,x is conv5i5t fir/ to det]m9e ! p]c5tage ( load relief to be effect$ 9 ! ma9 gird]s1 z to :i* x is to be obs]v$ t z ?is relief 7di/ribut$7 is induc$ by ! upw>d reaction ( ! new gird] act+ at ! c5tre ( ! cross-gird]s1 ! /ress relief ( ^! w1 z a rule1 greatly exce$ t ( ! outside gird]s4 ,= ! g5]ality ( cases1 x may be tak5 t ! relief suitable = ! outside gird]s w be satisfactory 9 its effects ^u ! cross-gird]s1 ev5 ?\gh x is desir$ to r$uce ! /ress 9 ^! to a great] degree4 ,if1 h[ev]1 x be ?\ght desirable to *eck ?is1 x may be done by consid]+ a cross-gird] subject to its dead & live loads act+ d[nw>ds1 & to reactions at ! c5tre & ends4 ,at ! c5tre ! reaction w be ! load ( :i* ! two ma9 gird]s are reliev$ on a l5g? equal to ! pit* ( ! cross-gird]s1 or z "h giv53-- c t ,p reaction at c5tre 7#a7 c be+ ! p]c5tage ( relief2 t ! total load p] foot run ( ! bridge2 & ,p ! pit* ( cross-gird]s4 ,! live loads c>ri$ by ! cross-gird]s are = ?is purpose tak5 at p] foot run1 z = ! ma9 gird]s4 ,) ^! data x w be easy to con/ruct a diagram ( mom5ts1 mak+ x evid5t :e!r ! relief propos$ = ! ma9 gird]s w give a suffici5t p]c5tage ( relief to ! floor beams4 ,grant+ t ?is proportion has be5 decid$1 & deal+ fir/ ) ! case 9 :i* ! c5tre gird] is simply atta*$ to ! cross-gird]s1 & takes no dead load o!r ?an its own weight1 !n ! live load c>ri$ by ! outside gird]s1 & previ\sly borne :olly by !m1 w be r$uc$ by ! am\nt x is int5d$ to transf] to ! c5tre gird]1 & w become ,ll - 7c ,lt7 live load on out] gird]s 7#b7 ,ll be+ ! total live load1 & ,lt ! total dead & live load c>ri$ by ! bridge4 ,f ?is ! deflection ( ! out] gird]s correspond+ to ?is modifi$ live load may be d]iv$4 ,illu/ration3 ,,fig4 #gj4 ,x is next necess>y to asc]ta9 ! v]tical movem5t1 commonly a depression1 ( ! cross-gird]s at ! c5tre relative to _! ends1 :5 subject to ! runn+ load only1 & support$ at ! middle & ends1 ! c5tre reaction be+ obta9$ z be=e indicat$ 7#a74 ,?is movem5t w be ! diff]5ce 7if any7 betwe5 ! deflection on ! :ole span ( ! cross-gird] due to ! live load1 & ! upw>d flexure ( ! gird] due to ! c5tre reaction1 consid]$ z sep>ate effects4 ,/ress values hav+ be5 e/imat$ = ! two conditions1 ^! results may readily be d$uc$ by simple flexure =mul1 obs]v+ t :ile ! curve ( mom5ts due to live load suffici5tly approximates to t = a di/ribut$ load to ju/ify1 = ?is1 ! use ( a di/ribut$ load =mula z giv5 9 ! *apt] 8,deflections10 ! flexure due to ! c5tre reaction w be b #jhj ( t :i* corresponds to ! same /ress = di/ribut$ load+4 ,or1 ! curve assum$ by ! gird] "u live load may be plott$ by a me?od to be lat] expla9$4 ,! sum ( ! movem5ts n[ det]m9$--t is1 ! live-load deflection ( ! out] gird]s1 & depression1 z is commonly ! case1 ( ! cross-gird]s--w give ! extreme depression 7m>k$ m 9 ,fig4 #gj71 f ! dead-load condition ( ! middle cross-gird]s1 :5 support$ to ! ext5t desir$ by a c5tre gird] ^: proportions are n yet kn[n1 b :i*1 c>ry+ ! requir$ p]c5tage ( ! total load1 mu/1 subject to a res]vation pres5tly /at$1 deflect only ?is am\nt4 ,! unit /ress 9 ! flanges ( ! new gird]1 gov]n$ by ?is flexure1 w = a plate gird] be ,d ,c m ----------- f1 unit /ress on gross section 7#c7 ,s#b ,d & ,s be+1 z be=e 7see 8,deflections071 ! dep? & span respectively 9 feet1 ,c a con/ant1 m ! deflection 9 in*es1 & f ! /ress p] squ>e in* on ! gross section ( flange4 ,! gross area ,a1 ( ! flange1 is giv5 by ,s c ,lt ---------------- gross area ( flange 7#d7 #h ,d f c ,lt1 be+1 z 9 7#b71 ! load transf]r$ to & c>ri$ by ! c5tre gird]4 ,! actual /ress 9 ! flanges w1 ( c\rse1 be great] by an am\nt due to ! gird]'s own weight2 b ?is does n affect ! "q ( relief4 ,= any ord9>y case ! /ress p] squ>e in* w be l[2 b x w manife/ly be useless to assume a great] /ress ) a view to economy1 z ! effect ( r$uc+ ! section w simply be to make ! gird] too flexible1 ?us caus+ x to be less effective ?an prim>ily int5d$4 ,if1 z is seldom ! case1 !re is fre$om z to ! dep? ( gird] p]missible1 x is evid5t ! unit /ress may be made a condition1 & ! dep? d$uc$ by a suitable modification ( =mula 7#c72 ! relief desir$ be+ 9 ?is way equally well assur$4 ,inde$1 9 ! r>e in/ances 9 :i* any dep? may be adopt$1 ?is me?od is--contr>y to ! g5]al rule--di/9ctly economical1 p>ticul>ly if ! gird] may be plac$ bel[ ! cross-gird]s1 :i* simply re/ ^u x1 )\t elaborate atta*m5ts4 ,illu/ration3 ,,fig4 #ga4 ,consid]+ n[ ! second me?od ( apply+ c5tre gird]s by :i* ! new gird] is made initially to c>ry "p ( ! dead load1 by adju/m5t1 x w at once be recognis$ z a m complex matt]4 ,! measure ( relief by :i* ! old gird]work %all b5efit ne$ n be affect$ by ! me?od ( apply+ ! c5tre gird]1 & may be decid$ on ! pr9ciples already consid]$4 ,! out] gird]s c>ry+ a r$uc$ load1 :5 ! bridge is fully load$1 & ! cross-gird]s be+ 9 "p support$ at _! c5tres 9 ! mann] already describ$1 w give a result+ depression m 7see ,fig4 #ga7 ( ! c5tre cross-gird]s1 bel[ ! orig9al dead-load position1 ( a simil> am\nt det]m9$ 9 ! same way4 ,?is extreme depression det]m9es also ! l[e/ position ( ! new c5tre gird]1 :i* may be design$ to c>ry ! requir$ p]c5tage ( ! total bridge loads ) ! maximum /ress & dep?1 z conditions1 leav+ ! initial dead load & necess>y adju/m5ts to be asc]ta9$4 ,?is is ! common case & w be "h dealt )1 x be+ assum$ to avoid ambiguity 9 description t ! new gird] lies above ! cross-gird]s4 ,! c5tre gird] ( fix$ dep? be+ !n requir$ to c>ry a def9ite load at a def9ite flange /ress1 w deflect a def9ite am\nt at ?is /ress4 ,if ?is deflection equall$ ! extreme depression m ( ! old gird] "w1 no adju/m5t w\ld be necess>y1 ! c5tre gird] !n c>ry+ no initial dead load1 z by ! fir/ me?od2 b = c5tre gird]s design$ = economical flange /ress ! deflection w 9 ord9>y cases greatly exce$ ?is1 ! dep? g5]ally be+ small1 & 9 ord] to ensure t ! new gird] %all d its full "w1 "s dead load mu/ be put ^u x4 ,9 ! act ( adju/m5t ! cross-gird]s mu/ be lift$ & ! c5tre gird] depress$1 till ! jo9t movem5t equals ! excess s ( ! c5tre gird] deflection ov] m1 :5 ! new gird] w c>ry ! prop] am\nt ( initial load1 & ^u fur!r deflection "u live load give ! full measure ( relief4 ,! am\nt ( 8lift0 or upw>d flexure ( ! old gird] "w1 & ! depression or 8drop0 ( ! new gird]1 dur+ adju/m5t1 w dep5d ^u relative /iffness1 & may be asc]ta9$ z foll[s3-- ,= unit reactions at ! c5tre ( ! cross-gird]s ! upw>d flexure ( ^! may be asc]ta9$1 z also ! upw>d flexure ( ! two out] gird]s :5 subject to =ces ( ! same total am\nt 7"o-half to ea*7 appli$ at ! cross-gird] ends4 ,! sum ( ^! movem5ts w give ! total lift ( ! c5tre cross-gird]s1 :5 all are subject to unit lift+ =ces2 simil>ly1 ! depression ( ! c5tre gird] = unit loads appli$ at ! cross-gird]s may be det]m9$4 ,!re w !n be kn[n ! movem5ts upw>ds & d[nw>ds ( ! old & new "w :5 be+ drawn toge!r by unit =ces appli$ z /at$4 ,if l lift due to unit loads1 lt total lift due to adju/m5t1 d drop due to unit loads1 dt total drop due to adju/m5t1 s deflection excess gross adju/m5t1 !re w !n be d --------- s dt1 l d total drop ( c5tre gird] "u adju/m5t1 l --------- s lt1 l d total lift ( c5tre cross gird]s "u adju/m5t1 dt ------ unit load d initial load put ^u c5tre gird] at ea* cross-gird]4 ,! rise ( ! two out] gird]s = upw>d =ces toge!r equal to ^? depress+ ! c5tre gird] may readily be d$uc$4 ,illu/ration3 ,,fig4 #gb4 ,illu/ration3 ,,fig4 #gc4 ,! act ( adju/m5t may conv5i5tly be effect$ by ! arrangem5t %[n 9 ,fig4 #gb1 9 :i* ea* cross-gird] is hung up at its c5tre by f\r bolts4 ,at ! middle ( ! c5tre gird] ! total am\nt to be screw$ up w be t correspond+ to ! deflection excess s1 b t[>ds ! ends ?is am\nt decreases1 & may advantage\sly be repres5t$ by a diagram z ,fig4 #gc1 9 :i*1 if s repres5ts to scale ! am\nt to be screw$ up at a c5tre cross-gird]1 ! correspond+ am\nts = o!r gird]s may be read (f direct4 ,x w be app>5t t x mu/ be necess>y to place ! c5tre gird] at su* a height z to leave a space betwe5 ! old & ! new "w great] ?an ! am\nt to be screw$ up1 ?is excess cle>ance be+ ultimately fill$ by a pack+4 ,! precautions to be obs]v$ 9 c>ry+ out ?is k9d ( "w1 & ! practical me?ods ( adju/m5t adopt$ by ! au?or aft] "s little exp]i5ce1 may "h be giv54 ,great c>e is necess>y at ! outset to asc]ta9 ! true spac+ ( ! cross-gird]s1 to ensure t ! bolt-holes 9 ! bottom flange ( ! c5tre gird] %all come :]e desir$4 ,! fix+ ( ! cross-gird] brackets also ne$s close att5tion to avoid aft] tr\ble1 ! bolt-holes 9 ! brackets be+ pref]ably drill$ on ! site aft] fix+4 ,x w1 = masonry abutm5ts1 be necess>y to fix b$/ones to receive ! new c5tre gird]1 :i*1 be+ c>ri$ out q possibly "u adv]se traffic conditions1 w p]haps leave ! /ones liable to settle slightly :5 ! full load is c>ri$4 ,to elim9ate ! bad effect ( ?is ^u ! ultimate adju/m5t1 & to take up any initial set ( ! new gird] "w1 :i* w\ld be prejudicial 9 ! same way1 x is desirable1 ! c5tre gird] be+ 9 place1 to screw up ! bolts tempor>ily & leave ! "w = a week or two4 ,to ensure regul>ity 9 ! screw+ up process1 x is conv5i5t to prep>e1 = use at ! bridge1 a diagram some:at simil> to ,fig4 #gc1 giv+ ! am\nt by :i* ! new & old "w are to be br\ght toge!r at ea* cross-gird]1 ) ! numb] ( turns = ea* nut to effect ?is4 ,) a man at ea* side ( ! gird]1 ! :ole l5g? is trav]s$1 giv+ a half-turn to ea* nut2 ?is is repeat$ z (t5 z necess>y1 & s manag$ z to br+ all up proportionately to ! f9al requirem5t1 keep+ tally ) *alk m>ks ov] ea* cross-gird] z a *eck4 ,! prelim9>y screw+ up %\ld be conduct$ ) little less c>e ?an t adopt$ = ! lat] adju/m5t1 to avoid damage to ! old "w4 ,?is lat] adju/m5t hav+ 9 due c\rse be5 effect$1 x is !n necess>y to measure = pack+s to fill ! spaces rema9+ betwe5 ! old cross-gird]s & ! new c5tre gird]4 ,^! spaces %\ld be callip]$ at ea* ( ! f\r corn]s1 c>e be+ tak5 to avoid aft]-confusion4 ,! measurem5ts asc]ta9$ w1 h[ev]1 be too great = ! f9i%$ pack+s1 z an all[ance ( n less ?an #a_/aj in* 7total71 w commonly be want$ to cov] irregul>ities 9 ! surfaces4 ,! pack+s1 hav+ be5 prep>$ & *eck$1 may be slipp$ into place aft] slack+ all ! bolts a small am\nt to p]mit ?is to be done1 f9ally screw+ up tight & secur+ ! nuts by split-p9s1 ?r\gh holes drill$ z ! la/ op]ation4 ,z a *eck ^u ! calculations & adju/m5t1 ! 8lift0 ( ! out] gird]s & cross-gird]s1 & ! 8drop0 ( ! c5tre gird] may be obs]v$ by levell+4 ,= ?is purpose ! au?or has us$ a /aff ( in*es divid$ into t5?s1 ) :i*1 & a good level1 v accurate read+s may be tak5 = %ort di/ances4 ,no ref]5ce has be5 made to ! effect ( skew 9 a bridge on ! above me?ods1 ! explanation giv5 apply+ r to bridges squ>e on plan4 ,! influ5ce ( skew on ! load di/ribution w l>gely be a matt] ( detail$ calculation4 ,! flexure ( ! gird]s may also be s5sibly affect$1 b may be arriv$ at ) suffici5t accuracy )\t any great tr\ble4 ,! *ief effect ( skew is to modify ! am\nt ( screw+ up dur+ adju/m5t1 :i* may be bett] und]/ood by ref]5ce to ,fig4 #gd1 & comp>+ x ) ,fig4 #gc1 ! adju/m5t diagram = a squ>e bridge4 ,to illu/rate h[ ^! me?ods ( /r5g!n+ "w out1 & comp>e z to weights ( c5tre gird]s requir$1 ! case has be5 assum$ ( a wr\ght iron bridge ( #fj-;feet span1 hav+ out] gird]s #e feet deep1 ( #ci squ>e in*es gross flange area2 & cross-gird]s1 at #h-;feet c5tres1 #bg-;feet span1 #a foot #i in*es deep1 ) a gross flange area ( tw5ty squ>e in*es4 ,! dead load & live load on ei!r road are ea* #age tons p] foot run4 ,! /ress 9 ! out] gird]s previ\s to ! alt]ation be+ #f tons p] squ>e in* gross1 x is desir$ to relieve ?is to ! ext5t ( #cc p] c5t4 by a /eel c5tre gird]4 ,9 ! table "h giv5 ! quantities giv5 9 italics are fix$ z prim>y conditions3-- ,,c5tre ,,/r5g!n+ ,,gird]s ,,= #fj-;,,ft4 ,,span4 ---------------------------------------- ----------------------- ,c5tre ,c5tre ,gird]1 ,gird]1 ,adju/m5ts ---- ,/ress ,dep? ,unkn[n4 ,unkn[n4 ,unkn[n4 ---------------------------------------- ----------------------- ,out] ,gird]4 ,deflection "u modifi$ live load #db 94 #db 94 #db 94 ,lift ( adju/m5t nil nil #aec ,cross ,gird]s4 ,depression "u live load --modifi$ conditions ( support #ac 94 #ac 94 #ac ,extreme depression 7m7 #ee #ee #ee ,lift ( adju/m5t 7cross- gird] only7 nil nil #jie ,total lift ( adju/m5t 7lt7 nil nil #bdh ,c5tre ,gird]4 ,dep? #ce ft4 #hb ft4 #ce ft4 ,unit /ress on gross section 7ex gird]'s weight7 #bad tons #ej tons #ej tons ,total deflection 7ex gird]'s weight7 #ee 94 #ee 94 #abh 94 ,deflection excess 7s7 nil nil #gc ,depression1 or 8drop0 ( adju/m5t 7dt7 nil nil #dhb ,gross area ( flange #aje sq4 94#aib sq4 94#dde sq4 94 ,weight #bj tons #ajd tons #aad tons ,net flange /ress 7includ+ gird]'s weight7 #cai tons #fhg tons #fid tons ---------------------------------------- ----------------------- ,gird]s subject to di/ribut$ load are treat$ z hav+ uni=m /ress1 b :]e ?is is n /rictly ! case1 z 9 "s light gird]s1 x w be necess>y to take ! fact into acc\nt4 ,= c5tre gird]s ( wr\ght iron1 & a unit /ress on ! gross section ( #d in/ead ( #e tons1 ! gird] weights are betwe5 #i & #aj p] c5t4 great]4 ,illu/ration3 ,,fig4 #gd4 ,9 ! above treatm5t ( ! application ( c5tre /r5g!n+ gird]s !re is a s\rce ( error :i* %\ld be t\*$ ^u4 ,if1 "u live load1 ! c5tre gird] deflects m ?an ! out] gird]s1 z x commonly w1 !re mu/ be a want ( uni=mity 9 ! behavi\r ( ! cross-gird]s1 ^? ne> ! abutm5ts be+ m reliev$ ?an ! e/imat$ am\nt ( relief ( ^? at ! c5tre1 :i* w h less ?an t int5d$2 b ! r$uction ( /ress 9 ! cross-gird]s w g5]ally be s consid]able t any su* ambiguity ( excess or defect is commonly unimportant2 ! effect ( ?is also ^u ! ma9 gird]s is mu* less ?an might be suppos$1 be+1 = ! ?ird ( ! cases j giv51 ab\t #b-a_/b p] c5t4 excess = ! c5tre gird]1 & g5]ally a mu* small] error4 ,) ?is qualification1 ! me?od c1 h[ev]1 be reg>d$ z approximate only4 ,x is possible to elim9ate "s "p ( ! error by lift+ ! end cross-gird]s dur+ adju/m5t1 a less am\nt ?an t giv5 by ! diagrams1 ,figs4 #gc & #gd1 tak+ c>e t ! c5tre gird] is depress$ its full am\nt by lift+ ! c5tre cross-gird]s a little m2 ?is ref9em5t is h>dly necess>y1 & unless controll$ by calculation _c be dep5d$ ^u = precise results4 ,p>ticul>s are "h giv5 ( five ord9>y cases1 comp>+ ! calculat$ & obs]v$ results ( adju/m5t4 ,! op]ation ( levell+ 0 conduct$ by a quick-ey$ & capable assi/ant1 :o 0 n made acqua9t$ ) ! results expect$1 9 ord] to avoid any sub-consci\s t5d5cy to mat* ! calculat$ figures3-- ,,examples ,,( ,,c5tre ,,gird] ,,adju/m5ts4 ---------------------------------------- --------------------------- -- ,calculat$4 ,obs]v$4 ---------------------------------------- --------------------------- 94 94 ,no4 #a4--ef-;,ft4 ,span4 ,depression ( c5tre gird] #hb #hd ,lift ( cross-gird]s at c5tre #bc #bb ,lift ( out] gird]s #bj #aj & #ac ,no4 #b4--eg-;,ft4 ,span4 ,depression ( c5tre gird] #ej #ej ,lift ( cross-gird]s at c5tre #ah #bj ,lift ( out] gird]s #aa #jh & #aj ,no4 #c4--fg-;,ft4 ,span4 ,depression ( c5tre gird] #gj #ge ,lift ( cross-gird]s at c5tre #ae #ag ,lift ( out] gird]s #aj #ji ,no4 #d4--fh-;,ft4 ,span4 ,depression ( c5tre gird] #gj #fe ,lift ( cross-gird]s at c5tre #bj #ah ,lift ( out] gird]s #ac #ad ,no4 #e4--eb-;,ft4 & #bh-;,ft4 ,spans cont9u\s4 ,long ,%ort,long ,%ort ,span4,span4,span4,span4 ---------------------------------------- ------------------------- 94 94 94 94 ,depression ( c5tre gird] #bh 44 #bi 44 ,lift ( c5tre gird] 44 #jd 44 #jc ,lift ( cross-gird]s 7c5tre ( spans7 #ag #ji #ae #ac ,lift ( out] gird]s #jh 44 #jh 44 ,depression ( out] gird] 44 #ja 44 negligible4 ---------------------------------------- ------------------------- ,! me?od ( calculation adopt$ = ^! cases 0 n precisely t giv51 ?\gh dep5d+ ^u ! same broad pr9ciples4 ,! fir/ _c be consid]$ a good example4 ,! la/1 hav+ cont9u\s gird]s1 ( c\rse ne$$ special treatm5t4 ,( ab\t sev5te5 bridges /r5g!n$ 9 ! mann] describ$1 ! effect g5]ally 0 satisfactory1 9 r$uc+ deflection & vibration2 b 9 two cases ( small span1 ow+ probably to settlem5t ( b$/ones1 ! results 7 n s good4 ,f fir/ to la/ ! "w ( putt+ 9 a c5tre gird] takes "s little "t1 ow+ to ! sl[ progress g5]ally made 9 fix+ ! brackets1 prep>+ pack+s1 etc4 ,! co/ ( a typical case 0 ab\t #bc p] c5t4 ( ! co/ ( a new sup]/ructure1 ) a #cj p] c5t4 relief ( /ress4 ,illu/ration3 ,,fig4 #ge4 ,illu/ration3 ,,fig4 #gf4 ,a special case ( /r5g!n+ by a c5tre gird]1 hav+ consid]able int]e/1 may be "h ref]r$ to4 ,! prim>y idea involv$ 0 n ! au?or's4 ,! bridge dealt ) has already be5 notic$ "u 8,brac+0 & a section1 be=e alt]ation1 %[n 9 ,fig4 #bf4 ,! span be+ #he feet1 !re 0 no room = a c5tre gird] ( suffici5t dep? above ! cross-gird]s & betwe5 ! roads1 nor 0 x consid]$ economical to place ! gird] :olly bel[ ! floor1 because ( ! co/ly /ag+ ?is w\ld h necessitat$ = erection purposes1 ! height above gr\nd level be+ v great4 ,a gird] 0 !re=e design$1 hav+ op5 lattic+ at an angle ( #fj degrees1 ) a bottom boom to be bel[ ! cross-gird]s1 ! top be+ z high above ! rails z c\ld be p]mitt$ 7see ,figs4 #ge & #gf74 ,a tempor>y boom 0 arrang$ at ! int]section ( diagonals1 ! l[] boom prop] n be+ fix$ till ! gird] hav+ be5 lift$ into place1 ) ! diagonal memb]s pass+ betwe5 ! cross-gird]s1 all[$ ?is to be done4 ,! gird] = "s "t c>ri$ itself f be>+ to be>+1 ) ! tempor>y boom 9 t5sion1 ! deflection be+ !n #b in*es4 ,! p]man5t boom 0 !n put 9 place1 & ! gird] re/or$ z ne>ly z 0 practicable to ! camb] x 0 int5d$ to h :5 complete1 b )\t ?r[+1 dur+ ! process1 any improp] loads ^u ! old "w4 ,! l[] boom be+ f9ally rivet$ up1 ! cross-gird]s 7 made to be> ^u x by suitable pack+s4 ,!re 71 9 addition to ! new gird]1 two /iff frames betwe5 ! old ma9 gird]s1 to :i* ! new 0 secur$4 ,! gird] 0 design$ ) ! int5tion t "u dead load only ! cross-gird]s %\ld j re/1 b ?r[ no weight1 ^u ! new "w1 ! latt] assi/+ to c>ry live load only4 ,! floor beams be+ ( small span1 & securely rivet$ to ! old gird] tops1 ! c5tre gird] 0 requir$ to deflect1 "u its %>e ( live load1 ! same am\nt z ! old ma9 gird]s "u ! rema9+ portion1 ! ?ree po9ts ( support ( ! cross-gird]s ?us n alt]+ _! relative levels4 ,t ?is result$ 0 evid5t f ! fact t1 previ\s to connect+ ! cross-frames to ! c5tre-gird]1 ! "w be+ o!rwise complete1 a space betwe5 ! two ( ab\t #a_/b in*1 aft]w>ds fill$ by a pack+1 %[$ no alt]ation1 ! close/ measurem5t fail+ to disclose any relative movem5t ^u ! passage ( live load4 ,! r$uction ( vibration 01 z might be expect$1 v m>k$4 ,9 ! conduct ( t class ( /r5g!n+ "w :i* has be5 dealt ) 9 ?is *apt]1 x is ess5tial1 9 ! au?or's judgm5t1 t ! man responsible = ! detail$ calculations & design %\ld himself see ! op]ations ( adju/m5t c>ri$ out1 or delegate x only to "o equally famili> ) ! requirem5ts4 ,be=e dismiss+ ! subject1 x w be well to ref] to a me?od ( approximately det]m9+ flexure curves1 ( occasional use 9 deal+ ) c5tre gird] or simil> que/ions4 ,! figure assum$ is plott$ to an exagg]at$ scale1 ) :i* object ! actual radius ( curvature at po9ts along ! gird]'s l5g? are fir/ asc]ta9$ by ! =mula ,e ,d ------- ,r1 radius ( curvature 9 feet1 f #b & ! radius ( curvature = ! diagram by #ab ,r ,f#b r1 radius = plott+1 9 in*es 7#e7 ,e be+ ! modulus ( ela/icity1 ,d ! gird]'s dep? 9 feet1 f ! mean ( ! extreme flange /resses p] squ>e in* ( gross area1 & ,f ! fraction indicat+ scale z #a_/dh1 :]e #a_/d in* #a foot4 ,! curve1 be+ plott$1 %[s by direct scal+ ! movem5t ( any po9t relative to its orig9al position4 ,ne> ! ends ( ! curve :]e ! radii may be ( consid]able l5g?1 ! arcs may be drawn ) ! help ( template curves1 or ev5 set out z pieces ( 8/raight40 ,:5 ! curve is laid d[n s t its *ord equals ! span to scale1 ! me?od involves an error ( excess 9 ! result+ deflection or droop :i* is z mu* z #g p] c5t4 :5 ! mean radius = plott+ equals ! span z drawn1 or :5 ! droop ( curve approa*es "o-eigh? ( ! span4 ,z ! exagg]ation ( curvature is made less pron\nc$1 ?is error rapidly dim9i%es1 till = a droop ( ab\t "o-sixte5? ! p]c5tage is "o-f\r? "p ( t above giv54 ,?is excess 9 ! droop ( curve may be am5d$ by ! foll[+ expression3-- 7droop#c 7 droop - 7------- #cgc7 correct$ droop1 or deflection4 7*ord#b 7 ,= "s purposes x may be pref]able to am5d ! radii = plott+1 s t ! curve1 z laid d[n1 %all be correct1 :i* may be effect$ by ! =mula "h giv51 to be appli$ to ea* value ( r1 z fir/ asc]ta9$3-- 7*ord#b 7 r 7------- #jfbe7 correct$ plott+ radius4 7 r 7 ,if1 h[ev]1 ! l5g? ( curve is made equal to ! span 7! *ord !n be+ less71 & ! radii = plott+ z giv5 by 7#e7 are us$1 ! result w = mo/ purposes be suffici5tly precise1 ?\gh !re w n[ be an error ( a contr>y k9d1 :i*1 = a curve hav+ a droop ( "o-eigh?1 w be ab\t #b p] c5t4 too little4 ,a some:at simil> me?od ( sett+ out deflection curves is describ$ by ,pr(essor ,fleem+ ,j5k9 9 ! article 8,bridges0 ( ! 8,encyclopdia ,britannica10 b )\t corrections4 ,a c>eful comp>ison ( results by ! above means1 ) ^? calculat$1 %[s t ) good draughtsman%ip !y may be reli$ ^u = consid]able accuracy4 ,equally applicable to gird]s ( v>y+ dep? & flange /ress1 !y h also a limit$ use 9 cases ( cont9uity4 ,illu/ration3 ,,figs4 #gg & #gh4 ,figs4 #gg & #gh illu/rate ! deflection & /ress diagrams = ! cross-gird]s ( ! bridge suppos$ to h be5 /r5g!n$ by a c5tre-gird]1 :5 "u ! influ5ce ( live load & a c5tre reaction ( a def9ite am\nt4 ,z a matt] ( conv5i5ce1 ea* radius l5g? has be5 halv$1 be=e correction1 s t ! result+ droop ( ! curve is twice ! true am\nt4 ,,*apt] ,,xii4 ,,ca/-,,iron ,,bridges4 ,ca/ ,iron z a mat]ial = bridges has ( late ye>s fall5 into disrepute4 ,x is n[ entirely taboo$ by ! ,bo>d ( ,trade = railway "u-bridges1 unless ( ar*$ con/ruction4 ,?is condemnation ( ca/ iron foll[$1 & 0 app>5tly ! result (1 an accid5t :i* occurr$ to an "u-bridge on "o ( ! s\!rn l9es1 :i* bridge _h already e>n$ = itself an ill repute by break+ d[n on a previ\s occasion4 ,! ultimate issue 01 h[ev]1 good1 inasmu* z x l$ to a ?or\gh ov]haul ( all railway "u-bridges 9 ?is c\ntry1 & ! r5ewal ( a great numb] no long] 9 a condition suit$ to ! c>riage ( heavy or ( pass5g] traffic2 yet !re is little d\bt t1 9 ! au?or's judgm5t1 _m excell5t ca/-iron bridges 7 !n remov$ at consid]able co/1 to be replac$ by o!rs ( wr\ght iron or /eel1 :i* w n la/ s long z _m ( ^? displac$ _h done1 or w\ld /ill h la/$ _h !y n be5 dismantl$4 ,! e>li] ca/-iron bridges 7 commonly made ( cold-bla/ iron1 a mat]ial ( su* /r5g? & t\ghness z to give an extraord9>y am\nt ( tr\ble 9 break+ up ! heavi] p>ts1 :5 ! "t arriv$ to d ?is1 & ) :i* mat]ial ord9>y hot-bla/ iron is n to be comp>$ = reliability4 ,illu/ration3 ,,fig4 #gi4 ,z illu/rat+ ! v consid]able /ress to :i* ca/ iron may be subject$1 )\t ( necessity lead+ to any mi%ap1 two cases may be cit$4 ,! fir/1 a bridge ( #cb feet effective span1 c>ry+ two l9es ( way1 ea* pair ( rails be+ support$ ^u ,b>l[ rails1 =m+ ! bridge floor1 ! ends re/+ ^u ! bottom flanges ( inv]t$ ,t-%ap$ gird]s1 #b feet #c in*es deep1 z %[n 9 ,fig4 #gi4 ,! extreme fibre /ress works out at #bi tons p] squ>e in* 9 t5sion1 & #ei tons p] squ>e in* compression1 calculat$ z x w\ld be 9 ord9>y (fice "w2 b = ! actual loads1 at a span z above1 exce$+ ! cle> span by #f in*es only1 & )\t reg>d to ! effects ( ecc5tric application ( ! load4 ,! gird]s :5 tak5 out %[$ ^u exam9ation no sign ( ov]/ra94 ,! practice ( load+ ca/-iron gird]s 9 ?is mann] _c1 h[ev]1 be too /rongly condemn$1 not)/&+ t 9 ?is case no ill result$4 ,x is evid5t t a piece ( ! l[] flange be+ brok5 out f ?is cause1 z occasionally happ5s1 might s r$uce ! section z to result 9 complete failure4 ,illu/ration3 ,,figs4 #hj & #ha4 ,! second example is t ( a small railway "u-bridge ( two spans1 cont9u\s ov] ! c5tral pi]1 ea* span be+ #af feet #f in*es4 ,! rails 7 support$ ^u longitud9al timb]s ly+ )9 tr\gh-%ap$ gird]s1 z %[n 9 ,figs #hj & #ha4 ,! /ress ov] ! pi]1 9 ! extreme fibres ( ! top flange1 is e/imat$ at #dg tons p] squ>e in* 9 t5sion1 b x %\ld be not$ t ! effect ( ! timb] longitud9al & rail has be5 neglect$ 9 arriv+ at ?is result1 :i* might possibly on ?is acc\nt be r$uc$ to ne> #c tons p] squ>e in*4 ,! case is noticeable because no evid5ce ( high /ress 0 app>5t4 ,! au?or saw no?+ to sugge/ s9k+ ( ! c5tral pi]1 ! effect ( :i*1 )9 limits1 w\ld be to fur!r r$uce ! /ress z calculat$2 b x is q possible "s slight settlem5t _h occurr$2 ?is1 z ! spans 7 s small1 w\ld h a s5sible effect4 ,:ile too mu* reliance %\ld n1 x is cle>1 be plac$ ^u any e/imat$ result ab\t :i* !re is a l+]+ d\bt1 x %\ld be rem>k$ t1 z x w\ld be necess>y ! pi] %\ld s9k #c_/af ( an in*1 = ea* ton ( r$uc$ /ress1 x is n probable t ! results quot$ are 9 excess to any mat]ial degree2 !y are1 inde$1 m probably l[1 z no notice has be5 tak5 ( impact4 ,?\gh ca/-iron gird]s = railway "u-bridges are n[ prohibit$ 9 ?is c\ntry = new works1 !re are /ill uses to :i* !y may be appli$1 & x may be well to insi/ t gird]s ( ?is mat]ial %\ld be fairly load$1 ! weight be+ br\ght ^u !m 9 su* a way t !re %all be no s]i\s second>y /ress1 su* z arises :5 wide flanges are made to c>ry conc5trat$ loads2 ! au?or has1 inde$1 met ) no in/ance ( a ca/-iron gird] break+ d[n "u a load fairly appli$4 ,pref]5ce is n[ giv5 to /eel or wr\ght iron = columns2 :ile ?is is (t5 q ju/ifiable1 !re rema9 _m cases 9 :i* no?+ bett] ne$ be desir$ = ?is purpose ?an good ca/ iron1 provid$ only t ! column be load$ 9 a suitable mann]--i4e41 axially1 & t ! arrangem5t & details ( ! sup]-/ructure are su* t !re %all be no cross-break+ ef=ts1 or rock+ ( ! column due to temp]ature or o!r causes2 unless1 inde$1 su* cross-break+ or rock+ is def9itely tak5 into acc\nt 9 design+ ! "w4 ,! same c>e obs]v$ 9 ! detail+ ( ca/-iron "w t is n infrequ5tly tak5 9 ! design ( /ructures made ( roll$ sections w\ld1 9 suitable cases1 ! au?or has no d\bt1 yield results j z reliable 9 practice1 ) ! advantage ( great] resi/ance to ru/1 & a r$uc$ co/ 9 ma9t5ance4 ,good ca/ iron is1 9 fact1 :5 us$ ) discretion1 a mo/ excell5t mat]ial1 popul> pr$judice not)/&+4 ,! olde/ metallic bridge 9 ?is c\ntry at ! pres5t mom5t is ( t metal4 ,! "o *ief respect 9 :i* ca/ iron is at a disadvantage comp>$ ) wr\ght iron or /eel is t x does n give premonitory w>n+ ( failure--x rema9s intact1 or x breaks4 ,! indications ( weakness1 :i* may be read by an exp]i5c$ inspector ( o!r metallic bridges1 are 9 a great measure abs5t4 ,!re is also an objection :i* may exi/1 b is to be avoid$ by good design & c>e 9 ! f\ndry--viz41 int]nal /ress due to unequal cool+4 ,9 extreme cases ?is may lead to fracture be=e ! "w has left ! mak]'s h&s1 b x c only occur by neglect ( ord9>y precautions4 ,illu/ration3 ,,figs4 #hb & #hc4 ,9 a case :i* has already be5 ref]r$ to 9 ! *apt] on 8,de=mations10 page #hj1 an out] rib ( a ca/-iron ar* fractur$ ne> ! cr[n aft] fifty-f\r ye>s' use4 ,ow+ to ! nature ( ! design1 & ! fact t ! ne> abutm5t _h clos$ 9 slightly1 br++ ! l9e> ar* ( necessity ne> ! l[] edges ( ! ar* segm5t 9 "q1 x 0 possible to e/imate1 ) a probability ( tru?1 ! extreme fibre /ress 7t5sile7 due to ! load =ces1 at ! upp] edge :]e fracture comm5c$4 ,! result 0 v f> f expla9+ ! occurr5ce ( ! break1 b an exam9ation ( ! details %[n 9 ,figs4 #hb & #hc w make x app>5t t1 9 addition to ! t5sile /ress1 z calculat$1 !re 0 probably a sev]e initial /ress ( ! same "* due to irregul> cool+ 9 ! f\ndry half a c5tury be=e4 ,! sum ( ^! /resses1 x is sugge/$1 plac$ ?is p>ticul> ca/+ 9 a critical condition1 su* t op]ations 9 ! con/ruction ( a new bridge adjac5t ei!r by produc+ a small fur!r settlem5t ( ! f\ndations1 ( :i* ! au?or saw no evid5ce1 or1 z is m probable1 ! atta*m5t ( a rope to ?is rib = ! purpose ( keep+ a b>ge 9 position1 :i* c]ta9ly did occur1 gave ! ar* rib j su* an additional /ra9 z to result 9 ! break %[n1 ?\gh no "o ( ^! causes act+ s+ly w\ld h be5 suffici5t to induce fracture4 ,! inn] ribs 7 ( a mu* less objectionable section4 ,illu/ration3 ,,fig4 #hd4 ,ca/-iron ar*es1 ?\gh /ill all[$ by ! ,bo>d ( ,trade rules1 are1 inde$1 liable to be s]i\sly affect$ by settlem5t1 or yield+ ( ! abutm5ts1 unless h+es at ! cr[n are introduc$4 ,z an in/ance ( ?is may be quot$ a bridge ( "s #de feet span1 9 :i* ! ar*es 7 ca/ 9 two pieces abutt+1 & v effici5tly bolt$ toge!r at ! cr[n1 ! spr++ & v]tical abutm5t memb] ( ! sp&rel be+ bolt$ & built solidly into heavy masonry4 ,! ar* sank at ! cr[n1 caus$ by1 or itself ! cause (1 a movem5t ( ! abutm5t1 ) ! result t ! l[] bolts at ! cr[n jo9t broke away1 ruptur+ ! ca/+1 z %[n 9 ,fig4 #hd4 ,! ar* mu/ !n h act$ z ?\gh h+$ at ! cr[n1 z effectiv5ess ( ! connection 0 de/roy$4 ,x _h be5 bett]1 evid5tly1 if a prop] h+e _h orig9ally be5 provid$4 ,! break happ5$ to occur s z to leave a suffici5tly good be>+ face at ! cr[n2 !re 01 inde$1 no t5d5cy = "o surface to slide ^u ano!r2 b 9 ! accid5tal fracture ( ca/ iron ?is _c be assur$1 & ! liability to x is a risk :i* %\ld be elim9at$ if possible4 ,a second case ( v mu* ! same "* has also be5 "u ! au?or's obs]vation1 ?\gh 9 ?is ! ends ( ! sp&rels 7 n built into ! brickwork ( :i* ! abutm5ts 7 compos$4 ,o!r in/ances ( fracture ei!r 9 ! ar* prop] or 9 ! sp&rel "w1 h come "u notice1 ?\gh p>ticul>s _c n[ be adduc$2 b ! examples cit$ are by !mselves suffici5t to ju/ify ! conclusion t x is imprud5t to con/ruct a ca/-iron ar* )\t a c5tral p9 or its equival5t1 unless ! abutm5ts1 be+ exceptionally well f\nd$1 may be reli$ ^u z free f any liability to move4 ,x is1 h[ev]1 to be borne 9 m9d t movem5t 9 ! abutm5ts ( a small ar* ( any giv5 absolute am\nt is m injuri\s ?an ! same am\nt ( movem5t 9 ! abutm5ts ( l>ge ar*es ( simil> design1 s t :at may be negligible 9 ! latt] case w\ld p]haps be de/ructive 9 ! =m]4 ,to ! abs5ce ( ductility & liability to initial /ress mu/ be add$ yet ano!r disadvantage to :i* ca/-iron "w is prone--viz41 ! possibility ( conceal$ defects1 bl[-holes or cold-%uts2 ^! 9 good f\ndry practice are n v likely to occur1 b1 z !y are possible1 _c be ov]look$ 9 consid]+ ! suitability ( ca/ iron = bridgework1 or1 inde$1 any /ructural "w liable to s]i\s /ress1 & p>ticul>ly t5sile /ress4 ,) ^! rem>ks by way ( qualification1 ! au?or reit]ates 8 op9ion t !re is /ill a use = ca/ iron 9 bridgework4 ,) respect to ! repair ( ca/-iron bridges1 b little is to be said2 ! possibilities 9 ?is direction are v limit$4 ,occasionally x may be desir$ to deal ) ! fracture ( "s memb] 9 ! sp&rel brac+ ( an ar*1 :5 x is commonly suffici5t1 & ev5 pref]able1 to limit ! repair "w to conf9+ ! fractur$ p>ts 9 su* a way z to prev5t displacem5t4 ,r>ely x may happ5 t an ar* fractures z a result ( settlem5t1 or o!r movem5t1 :51 if x is decid$ t safety ( ! /ructure is n imp]ill$1 x w 9 ?is case also be pref]able to conf9e ! p>ts simply by flit*-plates or o!r contrivance1 ) no attempt rigidly to make good ! break1 ! consequ5ces ( :i* treatm5t w\ld probably be to induce fracture 9 "s o!r place4 ,effective /r5g!n+ ( a ca/-iron /ructure is seldom practicable1 ?\gh some?+ may occasionally be done by ! negative process ( light5+ ! dead load1 or by remodell+ ! p]man5t way4 ,ar*es may1 h[ev]1 be r5d]$ mu* m reliable by ! introduction ( suitable brac+ :]e ?is is ei!r want+ or ineffici5t4 ,9 s*em+ su* additions x is desirable to arrange = z little drill+ ( ! old "w z is possible2 :]e ?is _c be altoge!r avoid$1 ! position ( ! holes %\ld be c>efully *os5 ) reg>d to ! effect !y may h ^u ! /r5g? ( ! old "w4 ,,*apt] ,,xiii4 ,,timb] ,,bridges4 ,timb] bridges1 ?\gh probably ! mo/ anci5t 9 type1 are yet ! lea/ durable 9 any p>ticul> in/ance4 ,! p]i%able nature ( ! mat]ial :5 us$ = expos$ con/ruction r5d]s x peculi>ly liable to develop defects :i* quickly put a limit to ! life ( ! /ructure4 ,9 addition to decay 9 ! body ( ! ma9 memb]s--:i* may p]haps be long delay$1 s t a simple beam bridge may la/ = _m ye>s--!re is 9 m complex designs decay at connections & jo9ts1 :i* proves v detrim5tal to ! integrity ( ! :ole4 ,wat] runn+ ^u ! surface ( a memb] gravitates to its l[] end1 &1 if !re be a jo9t or o!r connection1 settles !re1 to be productive ( la/+ mis*ief4 ,f ?is cause1 toge!r ) a v common defici5cy ( be>+ surface relative to ! =ces to be met1 ! jo9ts soon develop "s movem5t2 work+ ( ! /ructure comm5ces "u pass+ loads1 its f9al de/ruction be+ !n a "q ( "t only4 ,ea* jo9t is1 9 fact1 9 timb] bridge con/ruction a s\rce ( s]i\s weakness to a degree :i* has no p>allel 9 well-design$ metallic bridges4 ,wr\ght-iron /raps to conf9e ! ends ( rak+ memb]s1 or = o!r uses1 are liable to cru% into ! wood1 & bolts are apt to enl>ge ! hole ?r\gh :i* !y pass4 ,wood keys1 :]e ^! are introduc$ to prev5t "o timb] f slid+ ^u ano!r1 are also prone to develop cracks 9 ! ma9 memb]s1 & fibre crippl+ f excess ( /ress4 ,all ^! defects are1 h[ev]1 9 timb]-"w m easily def9$ ?an effici5tly rem$i$1 z x is b>ely practicable = any b ! h>d] woods to ensure1 = heavy loads1 a suffici5cy ( be>+ surfaces4 ,! mo/ readily detect$ evid5ce ( det]ioration 9 timb] bridges is ! sag ( its be>+ memb]s1 or trusses1 = ! simple reason t if !re is no local tr\ble at ! jo9ts1 !re w probably be no appreciable drop at ! c5tre ( ! span4 ,! exi/5ce ( su* a depression may1 h[ev]1 be caus$ 9 r>e in/ances by ! spread ( ! support+ pi]s or abutm5ts1 p>ticul>ly 9 ! case ( beams truss$ by end diagonal rak]s & hav+ no tie4 ,bridges =m$ ( deep trusses1 ) ! road ^u ! top1 are sometimes f\nd to be want+ 9 lat]al brac+1 ! result ( :i* is t ! ma9 trusses g out ( l9e1 lean+ consid]ably "o way or ! o!r1 be+ *eck$ only by su* rigidity z ! jo9ts & floor-beam atta*m5ts may h1 ) possibly "s assi/ance f ! end connections ( ! span4 ,! decay ( piles :]e ent]+ ! gr\nd or wat] is1 ( c\rse1 a fruitful s\rce ( tr\ble1 z also is ! s9k+ ( piles1 :]e ^! are insuffici5t 9 numb]1 or h n be5 well driv5 9 ! fir/ place4 ,a vital difficulty ) timb] /ructures g5]ally is ! unc]ta9ty t w commonly exi/ z to h[ f> decay ext5ds 9 ^? cases :]e x has />t$4 ,timb] does n necess>ily %[ ^u its surface ! evid5ces ( int]nal rott+4 ,memel timb] may1 inde$1 be sometimes f\nd to h become ?or\ghly unreliable1 yet %[+ no sign ( ?is ^u its pa9t$ surface4 ,by s\nd+ ! wood ) a hamm]1 or by prob+1 its condition may commonly be asc]ta9$4 ,9 cases ( d\bt1 an aug]-hole w make x cle> z to :e!r ! int]ior be good or o!rwise1 z to ! p>ticul> p>ts te/$2 b only z to ^? p>ts1 leav+ x a matt] ( guesswork z to ! rema9d]4 ,illu/ration3 ,,fig4 #he4 ,a railway bridge hav+ _m ( ! defects :i* h be5 indicat$ may be quot$ z an example4 ,?is /ructure cross$ a canal1 support$ ^u piles1 "s ( :i* 7 9 wat]1 o!rs c>ry+ l& spans4 ,! canal span consi/$ ( f\r trusses1 "o "u ea* rail1 or ne>ly s1 fram$ 9 ! mann] %[n 9 ,fig4 #he1 precise details n1 h[ev]1 be+ n[ available4 ,! trusses1 ap>t f deflection "u live load1 sagg$ consid]ably--9 "o in/ance1 #d-a_/b in*es2 "o inside truss 0 also lean+ t[>ds ! c5tre l9e ( ! bridge z mu* z #c in*es4 ,"o rak]1 or diagonal /rut1 0 rott$ half ?r\gh its ?ickness1 & _m o!r timb]s 7 badly decay$4 ,! end connections & jo9ts 7 also 9 a bad condition4 ,! v]tical tie-bolts ( ! ma9 trusses 7 all slack4 ,! piles g5]ally1 _m ( :i* 7 badly decay$1 _h sunk & incl9$ t[>ds "o end ( ! bridge ab\t #d in*es 9 #g feet ( height1 ! gr\nd be+ s(t & unreliable4 ,movem5t "u a pass5g] tra9 crawl+ ov] ! bridge 0 v appreciable1 b n />tl+4 ,!re _h be5 introduc$1 f "t to "t1 additional timb]s & iron ties1 ) ! object ( r5d]+ ! spans m reliable1 b leav+ x some:at difficult to det]m9e ! function ( ! sev]al memb]s4 ,! bridge 01 ( c\rse1 recon/ruct$4 ,illu/ration3 ,,fig4 #hf4 ,illu/ration3 ,,fig4 #hg4 ,illu/ration3 ,,fig4 #hh4 ,an in/ance may "h be cit$ %[+ h[ badly di/ort$ a timb] /ructure may become )\t actually fall+4 ,! bridge ref]r$ to consi/$ ( ?ree spans ( #bi feet1 ea* span hav+ two trusses1 betwe5 :i* ran a colli]y tramroad1 #a-;foot #f-;in* gauge2 ! corves runn+ ^u ?is1 at #d feet #f in* c5tres1 weigh$1 :5 full1 ab\t #aj cwt4 ea*4 ,! trusses 7 badly out ( %ape1 ! c5tre span hav+ sagg$ #e-a_/b in*es1 ) "o truss ( ! same span ne>ly #aj in*es out ( l9e at ! c5tre4 ,?is little bridge1 ( :i* "s details are %[n 9 ,figs4 #hf1 #hg1 & #hh1 _h be5 9 use ab\t tw5ty ye>s4 ,illu/ration3 ,,fig4 #hi4 ,a ?ird case :i* may be nam$ is t ( a road bridge1 ab\t #ab feet wide1 cross+ by ?irte5 spans a %all[ riv] liable to floods4 ,! con/ruction 0 ( a simple "*1 z indicat$ 9 ,fig4 #hi1 & consi/$ ( piles support+ truss$ beams1 :i* _h sagg$ 9 "s in/ances ov] #b-a_/b in*es4 ,! bridge _h1 "s ye>s previ\s to ! au?or's inspection1 be5 heavily repair$1 _m new /rut & /ret*+ pieces hav+ be5 introduc$1 ! piles also be+ re9=c$ or r5ew$4 ,five ye>s be=e1 a traction eng9e1 said to weigh #e tons1 _h pass$ across ! bridge 9 safety2 b ! au?or notic$ t a coal wagon1 :i*1 ) ! horse1 weigh$ ab\t #ej cwt41 :5 walk$ sl[ly ov] set up mu* movem5t4 ,?is bridge _h be5 9 use ne>ly ?irty ye>s1 & 0 v mu* out ( l9e f end to end4 ,?\gh timb] bridges _c at ! be/ be consid]$ durable1 yet1 by att5tion to c]ta9 po9ts 9 design & con/ruction1 _! l5g? ( life may be mat]ially enhanc$4 ,e cut across ! gra9 may be consid]$ an elem5t ( weakness by expos+ ! mat]ial to quick] decay1 = :i* reason ! numb] ( ends1 or ( jo9ts1 %\ld be r$uc$ to a m9imum4 ,an additional reason = r$uc+ ! numb] ( jo9ts or o!r connections is ! liability ( ^! to develop movem5t1 z already /at$1 ! yield ( any "o jo9t1 be+ ! cause ( movem5t 9 o!rs1 :i* might1 b = ?is1 h rema9$ close4 ,^! consid]ations lead to ! conclusion t fewness ( p>ts is1 9 timb] con/ruction1 z 9 /ructural "w g5]ally1 an excell5t pr9ciple to obs]ve4 ,mortis+1 elaborate sc>f jo9ts1 recess+1 or any cutt+ into ! timb] :i* is n ess5tial1 %\ld be avoid$1 ! simple/ =ms ( connection be+ pref]able1 if at all suitable4 ,if a /ep or butt surface is want$ = any memb]1 x is commonly bett] to provide ?is by a cleat or o!r add$ piece1 r ?an by cutt+ into ! timb] butt$ aga9/4 ,a complicat$ jo9t =m$ 9 ! body ( ma9 timb]s c only be r5ew$ by r5ewal ( ! timb] itself1 :]eas by ! me?od indicat$ ! jo9t is readily tight5$1 or re-made1 )\t involv+ ! ma9 memb]4 ,be>+ surfaces %\ld be ample1 /raps ( lib]al dim5sions1 & bolts l>ge 7) good wa%]s71 bo? = ! sake ( be>+ surface 9 ! holes1 & r$uction ( any liability to b5d "u cross-/ress4 ,9 trusses ( ! =m %[n 9 ,figs4 #he & #hf1 x is desirable to introduce diagonal memb]s 9 ! middle bay1 ev5 ?\gh x may appe> t ! /iffness ( ! ma9 beams is suffici5t to r5d] ?is unnecess>y z a matt] ( /r5g?1 z )\t ^! !re is apt to be1 "u roll+ load1 a slight di/ortion1 lead+ to work+ ( ! jo9ts & free entry ( moi/ure4 ,lat]al brac+s %\ld also1 = mu* ! same reasons1 be introduc$1 ev5 ?\gh !y may n appe> necess>y 9 ! new /ructure1 ) jo9ts all close & effective4 ,project+ ends ( timb]s %\ld be c>ri$ out well beyond ! requirem5t ( /r5g? or be>+1 9 ord] to ensure a lib]al m>g9 = t decay 9 ! end fibres :i* commonly develops4 ,timb]s re/+ ^u abutm5ts1 or runn+ into conf9$ spaces1 %\ld be arrang$ = free v5tilation & ready dry+4 ,occasionally jo9ts at ! l[] ends ( timb]s are protect$ by lead or z9c fla%+s to prev5t wat] runn+ into !m1 a me?od :i* %\ld h "s protective value4 ,:atev] measures may be adopt$1 :e!r 9 ! design or execution ( timb] bridge-"w1 w1 h[ev]1 be b little effective1 if ! timb] itself is n good ( its k9d1 & well season$4 ,creosot+ to be useful %\ld be ?or\gh & some?+ m ?an sk9 deep4 ,! timb] itself %\ld be well dri$ be=e treatm5t4 ,! repair ( timb] bridges v l>gely consi/s 9 ! r5ewal ( decay+ timb]s1 :]e ?is is practicable1 or 9 add+ supplem5t>y pieces :]e ! old _c conv5i5tly be displac$4 ,jo9ts may be tight5$ up by h>d-wood w$ges1 prop]ly secur$ to prev5t slack+ back1 all bolts be+ also screw$ up tight1 p]haps "s additional be+ introduc$4 ,piles /&+ 9 wat]1 :i* h decay$1 may be /r5g!n$ by driv+ o!r piles betwe5 ! old1 or on ei!r side1 b n ( necessity opposite to !m1 & by means ( wal+ timb]s bolt$ to ! old piles1 put 9 a position to take load1 ei!r by ! wal+s re/+ ^u _! tops1 or be+ bolt$ to !m4 ,piles decay$ :]e ent]+ solid gr\nd may g5]ally be /r5g!n$ by bolt+ on supplem5t>y timb]s to rea* well above & bel[ ! decay$ "p1 or by cutt+ out ! bad l5g?1 introduc+ a new piece1 & fi%+ ! butt-jo9ts 9 a prop] mann]4 ,b all rem$ial measures h g5]ally to be consid]$ ) ref]5ce to co/1 z comp>$ ) ! probable increase ( life ( ! /ructure4 ,) a bridge 9 an advanc$ /ate ( decrepitude1 su* repairs may prove any?+ b economical1 & at ! be/ def] recon/ruction b a v mod]ate l5g? ( "t4 ,,*apt] ,,xiv4 ,,masonry ,,bridges4 ,masonry bridges1 9 :i* description x is int5d$ to include /ructures bo? 9 /one & brick1 are1 :5 well built1 among/ ! mo/ durable & long-suff]+ ( any :i* come "u ! c>e ( a ma9t5ance eng9e]2 yet :5 develop+ ! faults peculi> to _! k9d1 !y may be ! occasion ( mu* anxiety1 & r5d] necess>y frequ5t inspection1 or ev5 cont9u\s wat*+4 ,ap>t f decay ( mort> or mat]ial1 defects may v commonly be trac$ to ! f\ndations1 or to e>?-slips4 ,s9k+1 :5 uni=m1 may be q h>mless1 ?\gh possibly inconv5i5t2 irregul> s9k+ ( pi]s or abutm5ts is q a diff]5t matt]4 ,x is1 h[ev]1 rem>kable to :at a degree s9k+ may be evid5t1 )\t ( necessity r5d]+ a /ructure unsafe4 ,movem5t ( an am\nt & k9d :i* w\ld be fatal to ! connections ( metallic bridgework is endur$ by bridges ( /one or brick2 n1 x may be1 )\t damage1 yet ) no occasion = al>m4 ,! sup]/ructure ( metallic bridges may (t51 h[ev]1 be re/or$ to ! true level be=e ! mis*ief has become s]i\s1 :]eas 9 ! case ( masonry ar*es ?is is n practicable4 ,spread+ ( ! abutm5ts is v seldom ! cause ( any great injury to an ar*1 ?\gh x is common en\gh to f9d old & flat ar*es slightly d[n at ! cr[n2 b ! contr>y case ( abutm5ts clos+ 9 is n v unusual :5 ^! are high1 or t]m9ate a viaduct ov] a deep valley4 ,su* an abutm5t may move dur+ or soon aft] con/ruction1 ?r[+ up ! cr[n ( ! end span affect$2 or1 if ! ar*es are v solid & heavy1 ! abutm5t may slide =w>d at ! base1 ) no s5sible r$uction ( ! op5+4 ,:5 a viaduct connects ! two ends ( a high embankm5t1 x may happ5 t ! end pi]s are n cle> ( ! embankm5t slope1 9 :i* ev5t a pi] may1 %\ld ! bank slip1 move ) x1 z to t "p n 9 solid gr\nd2 ) ! result1 9 a bad case1 t x is brok5 across & ! sup]/ructure imp]ill$4 ,illu/ration3 ,,fig4 #ij4 ,a case ( abutm5t movem5t is illu/rat$ 9 ,fig4 #ij1 :i* repres5ts ! end ar* ( a masonry viaduct1 "o abutm5t ( :i* _h mov$ =w>d 9 ! mann] already ref]r$ to4 ,f ! spr++ upw>ds ! ar* reta9$ its =m to )9 a %ort di/ance ( ! cr[n1 :]e x 0 =c$ up 9 ! way indicat$4 ,:5 ! movem5t became pron\nc$1 heavy timb] c5t]+ 0 introduc$1 ) ! object ( prev5t+ any mi%ap1 ! damag$ portions be+ ultimately cut out & made good4 ,! /ructure 0 ?irty-five ye>s old4 ,! practical utility ( /op pi]s 9 long ar*$ viaducts is1 p]haps1 r 9 *eck+ movem5t ( ! tops ( pi]s "u mov+ load ?an 9 arre/+ actual failure ( a s]ies ( ar*es4 ,t ! tops ( pi]s d move v s5sibly ne$ n be d\bt$4 ,! au?or has attempt$ to measure ?is 9 ! case ( pi]s ab\t #fj feet to ! spr++1 by means ( a !odolite plac$ bel[1 b has rea*$ no m def9ite result ?an t a movem5t exi/$1 ( :i* he 0 n able to det]m9e ! am\nt4 ,if 9 a viaduct "s ar*es are m heavily load$ ?an o!rs1 ea* spread+ slightly1 ! end pi]s ( ! gr\p w move am\nts :i* toge!r equal ! sum ( ! individual span spreads1 ) a t5d5cy 9 ! ar*es beyond ^? ( ! gr\p ov]load$ to rise4 ,?is rock+ may be detrim5tal bo? to ! pi]s & ar*es1 & helps to acc\nt = ! dis9tegration ( mort> 9 ar*es & pi]s1 :i* n infrequ5tly happ5s4 ,! s(fits w sometimes be se5 ) a ?ick incru/ation ( lime1 :i* has wa%$ out ( ! jo9ts1 or f lime/one balla/ above1 :]e ?is has be5 9 use4 ,ar*es ( tall viaducts may1 inde$1 become 9 s bad a condition t pieces ( /one or brick w drop out1 necessitat+ repair at heavy exp5se1 ( :i* scaffold+ is commonly a l>ge "p4 ,tall pi]s may be f\nd badly out ( ! upright due to s9k+ ( f\ndations4 ,a m>k$ case ( ?is k9d came "u ! au?or's notice--a viaduct ( fifte5 semicircul> ar*es1 9 :i*1 ?\gh _m pi]s 7 want+ 9 tru?1 "o 9 p>ticul> 0 ab\t #a foot #d in*es out ( v]tical1 mak+ "o side ( ! %aft plumb1 & d\bl+ ! normal batt] ( ! o!r4 ,inquiry %[$ t 9 ?is in/ance ! pi] _h nev] be5 upright f its e>lie/ hi/ory dat+ back ?irty-six ye>s4 ,?is makes cle> ! desirability1 to avoid ha/y conclusions1 ( asc]ta9+1 :5 x is possible to d s1 ! complete record ( any /ructure4 ,a bridge fifty-eight ye>s old1 ( ?ree skew spans1 c>ry+ a railway ov] a canal1 & hav+ some:at flat brick ar*es ) /one quo9s ^u l[ pi]s1 develop$ ! some:at unusual defect1 z to ! c5tre ar*1 ( splitt+ along its l5g? = ab\t #aj feet1 p>allel to & "s #g feet f "o face4 ,9 ?is case !re 0 reason to believe t !re _h be5 consid]able local settlem5t ( ! pi]s on t side ( ! bridge4 ,! ar*es 7 o!rwise 9 bad condition1 ! brickwork poor1 & ! mort> decay$4 ,ea* ar* 0 d[n at ! c5tre1 & display$ a fault n unusual :]e bad brickwork jo9s up to good cut /onework1 ! quo9s %[+ a t5d5cy to sep>ate f ! brick r+s4 ,bel[ ! bridge 7 coal-work+s4 ,brick ar*es built 9 p>allel r+s sometimes sep>ate "o r+ f ! o!r1 demon/rat+ ! kn[n propriety ( bond+ ! r+s toge!r prop]ly1 & ( c>ry+ ! ar* r\nd1 :5 build+1 at its full ?ickness4 ,illu/ration3 ,,fig4 #ia4 ,an in/ance ( bridge failure f a some:at peculi> cause may be quot$ z ( "s int]e/1 l>gely because ! /ructure 0 v anci5t1 hav+ be5 9 exi/5ce "s #djj ye>s4 ,?is bridge1 c>ry+ a road1 0 ( ! type usual 9 old masonry bridges ov] a riv]1 hav+ small ar*es1 ?ick pi]s1 & solid back+s to ! ar*es4 ,two flood-op5+s at "o end _h1 by s9k+ & want ( c>e1 become p>tly clos$4 ,! c5tre ar* _h1 h[ev]1 be5 wid5$ ab\t #adj ye>s previ\sly4 ,dur+ a sev]e flood1 ! swoll5 riv]1 ov]fl[+ its banks1 trespass$ ^u a timb] y>d a little above bridge1 & wa%$ d[n into ! /ream a l>ge quantity ( sawn timb]2 ?is1 unable to get ?r\gh ! ma9 ar* ) fre$om1 compact$ into a s]i\s ob/ruction4 ,! flood wat]1 ?us *eck$ 9 its passage1 seems to h sc\r$ bel[ ! timb]1 & robb$ ! pi]s ( su* support z !y =m]ly _h 7see ,fig4 #ia74 ,! bridge /ood 9 ?is condition till ! wat] l[]$1 :5 ! middle "p ( ! /ructure broke up1 & subsid$ into ! hole :i* _h be5 wa%$ out4 ,b = ! monoli?ic "* ( ! old "w x is probable ! bridge w\ld h fail$ long be=e1 z ! gravel b$ on :i* ! pi]s /ood _h be5 p>tly und]m9$ = v _m ye>s4 ,! case is in/ructive1 z %[+ h[ a slight accid5t--p[]less by itself to "w mis*ief--may be v damag+ :5 alli$ ) s p[]ful an ag5t z runn+ wat]4 ,illu/ration3 ,,fig4 #ib4 ,! endur+ "* ( ev5 ! r\ghe/ class ( masonry ar*1 if only ! mat]ial be good & abutm5ts /able1 is %[n :5 x becomes necess>y to de/roy old "w ( ?is "*4 ,fig4 #ib repres5ts a %ort l5g? ( 8cut & cov]0 ar*+ 9 process ( demolition1 j be=e x fell 94 ,! masonry 0 ( h>d s&/one rubble & _h be5 cut away1 z %[n1 till at ! po9t ,a only a v small piece ( ! ar* rema9$1 :5 ! l5g? f9ally broke up & dropp$4 ,ar*es h commonly a great res]ve ( /r5g?2 tunnel l9+s are1 inde$1 (t5 badly out ( %ape1 clos$ 91 & sunk52 yet cont9ue1 ) close wat*+1 & occasional repairs :]e ! "w has decay$ or bulg$1 to s]ve ! purpose int5d$4 ,?\gh ! equilibrium ( masonry ar*es has be5 ! occasion ( mu* pr(\nd /udy1 & ! nice/ calculation has sometimes be5 appli$ to ! design ( su* "w1 yet x appe>s t :5 an ar* is well back$ up1 ! !oretical l9e> ar* ne$ h b little connection ) ! figure ( ! intrados2 a /atem5t consonant bo? ) common-s5se & ! tea*+s ( exp]i5ce4 ,) solid back+1 ?is w\ld inde$ seem to be m important ?an any "p ( ! ar* r+ bel[ ! top ( ! back+1 ! l[] "p ( ! r+ s]v+ *iefly to pres]ve ! face ( ! solid "w4 ,ar*es are frequ5tly to be met ) s out ( _! true %ape t b = ! consid]ation nam$1 failure w\ld seem to be inevitable4 ,! masonry or brickwork does n always %[ evid5ce ( damage1 if ! di/ortion has be5 sl[2 sugge/+ t /ructures ( ?is k9d h a p[] ( accommodation ) :i* !y are n g5]ally cr$it$4 ,a noticeable cause ( det]ioration ( masonry /ructures1 :i* may be q indep5d5t ( settlem5t1 is s]i\s vibration4 ,?is is well kn[n 9 connection ) *ur* belfries1 & is also locally app>5t :5 telegraph or o!r poles are atta*$ to masonry p>apets4 ,vibration1 :5 caus$ by heavy railway traffic1 act+ ^u ar*es light or orig9ally bad1 may demoralise ! /ructure to su* an ext5t t repair becomes exce$+ly difficult1 because ( ! ext5sive "* ( ! mis*ief2 b masonry bridges sub/antially built1 & p>ticul>ly ^? c>ry+ ord9>y roads1 & n subject to mu* vibration1 h great la/+ p[]s1 if repair$ ) skill1 or ev5 let alone4 ,di/ortion ( ! ar* may be q consi/5t ) practical /ability1 if ! movem5t or decay ) :i* x orig9at$ is n progressive1 or has be5 arre/$4 ,9 ?is connection a di/9ction is to be made betwe5 ar*es well back$1 to :i* ! =ego+ rem>ks apply1 & 9 :i* ! two halves ( ea* ar* may act z sep>ate monoli?s meet+ at ! cr[n1 & ! case ( a true ar* r+ indep5d5t ( any outside resi/ance1 su* z back+ or sp&rels may give1 & dep5d+ almo/ :olly ^u ! prop] balance ( its compon5t v\ssoirs = its /ability4 ,) ! latt] class ( /ructure no lib]ties may be tak52 :il/ ) ! =m] !re is seldom cause = fe>1 if ! f\ndations d n give way1 & ! "w is dealt ) judici\sly1 if at all4 ,x mu/1 h[ev]1 be und]/ood t !re are limits z to :at may be done effectively1 %ort ( rebuild+1 9 deal+ ) /ructures 9 :i*1 p]haps1 brickwork is rott5 & mort> decay$ & crumbl+1 ! :ole be+ little bett] ?an a brok5 mass ( rubbi%4 ,9 cases :]e x may be prud5t to introduce safety c5tr+1 z 9 an in/ance already ref]r$ to1 x is commonly exp$i5t to refra9 f caus+ ?is to take any s5sible "p ( ! load till all movem5t has ceas$1 ! c5tres be+ at ! outset l>gely precaution>y4 ,! requirem5t ) an ar* 9 bad condition is to avoid di/urb+ x = ! worse4 ,if ! c5tres are w$g$ up :il/ movem5t is /ill go+ on1 ! effect may be to cause ! ar* to break up ^u ! c5tr+1 & precipitate repair "w :i* might o!rwise h be5 left to a m conv5i5t "t1 :5 all movem5t _h /opp$ or be5 *eck$ by suitable measures4 ,viaduct ar*es 9 a bad condition1 b n necessitat+ ! use ( relief c5tres1 are commonly dealt ) piecemeal by cutt+ out ! bad places1 a small "p at a "t1 & mak+ good4 ,! "w requires ! greate/ c>e ( exp]i5c$ m54 ,po9t+ masonry or brickwork is effective = little o!r ?an protective purposes1 & to *eck fur!r wea!r+2 x has obvi\sly no effect ^u ! int]ior "w1 & if made to cov] up ! evid5ces ( int]nal decay1 is ev5 mislead+ & objectionable4 ,9 extreme cases x may be desirable to op5 out ! road & deal ) ! fill+1 to relieve or to /r5g!n ! out] sp&rel walls1 :i* sometimes bulge1 or = o!r purposes1 z1 = example1 = rebuild+ inn] sp&rel walls1 gr\t+ up or o!rwise repair+ solid back+1 9 :i* op]ations "s reg>d mu/ be _h to ! effect ( ! "w ^u ! balance ( ! oppos+ halves ( ! ar*4 ,( ! diff]5t classes ( masonry commonly us$ 9 bridgework1 x may be well to rem>k t good c\rs$ rubble1 or pref]ably t v>iety bond+ bo? v]tically & horizontally1 ( a durable /one1 p]haps q unfit = any b r\gh dress+1 may make a mo/ la/+ /ructure1 ! mort>1 ( c\rse1 be+ good4 ,ea* r\gh-dress$ /one pres5ts a durable piece1 fragm5ts remov$ sep>ate f ! block1 probably along "s l9e ( relative weakness--!re is no 8nurs+0 ( weak corn]s2 :]eas ) /ones r$uc$ to a p]fectly regul> %ape by *isel "w1 ! plane surfaces & geometrical angles are made ) p>tial reg>d only to ! natural gra9 ( ! /one4 ,,*apt] ,,xv4 ,,life ,,( ,,bridges--,,relative ,,m]its4 ,! life ( bridges ( diff]+ mat]ials has be5 incid5tally t\*$ ^u by ! examples quot$1 9 deal+ ) ea* class ( /ructure4 ,x w be useful to recapitulate "s ( ! facts adduc$1 & to comp>e ! t]ms ( life s f> z !y appe> to be indicat$2 b 9 do+ ?is x is necess>y to rememb] t ! life ( a bridge ( any "o mat]ial is insep>ably connect$ ) its own private hi/ory4 ,! duration ( any su* /ructure may be limit$ by adv]se conditions1 peculi> to ! case consid]$1 by defects ( design1 mat]ial1 or workman%ip--pres5t f ! fir/--or by neglect1 ov]load+1 or accid5t1 mak+ up its lat] record4 ,) ! exception ( timb] /ructures1 x is difficult to f9d any class ( bridges furni%+ examples :i* h rea*$ ! limit ( life1 indep5d5tly ( ! evils nam$1 & z a result ( unavoidable decrepitude4 ,!re are none ! less influ5ces at "w t5d+ to ?is condition1 & :i* x is too mu* to expect c 9 all cases be =ese5 or completely gu>d$ aga9/1 su* z ! %ift+ or sc\r+ ( riv]-b$s1 settlem5t ( f\ndations1 natural decay1 & m9or faults 9 design1 :i* ev5 9 ! mo/ capable h&s may be expect$ ev] to fall %ort ( p]fection4 ,at ! be/1 !n1 ! life ( any /ructure1 ?\gh long1 mu/ h a limit4 ,) bridges ( m av]age or inf]ior qualities ! life may be positively %ort1 ev5 )\t ! de/ructive influ5ce ( ov]load+4 ,deal+ ) in/ances ( metallic bridges1 ! adjac5t table gives ! "t ea* _h be5 9 exi/5ce :5 remov$1 & "s indication ( ! reason = its condemnation4 ,^? m>k$ ) an a/]isk 7 cases ( pron\nc$ high /ress4 ,f a /udy ( ! table x appe>s t 9 actual practice1 mak+ no excuses ( any sort1 ! l5g? ( life ( ! wr\ght-iron bridges specifi$ v>i$ betwe5 twelve & ?irty-six ye>s2 b ^! figures appli$ to ?is collection ( cases only4 ,x is to be rem>k$ t _m o!r bridges outla/$ ^!1 & are likely to cont9ue reliable4 ,^! results %[1 !n1 no m ?an t "s wr\ght-iron bridges are %ort-liv$1 hav+1 9 fact1 be5 select$ z examples ( ?is4 ,long]-liv$ exceptions are useful1 z indicat+ t ! durability ( su* /ructures is by no means s limit$ z ! table w\ld sugge/4 ,x is to be obs]v$ t1 z design & ma9t5ance are n[ bett] & m g5]ally und]/ood ?an :5 exp]i5ce 0 l>gely want+1 x is to be expect$ t lat] examples w %[ no su* poor results4 ,( /eel bridges little c be said1 because ( ! limit$ "t ?is mat]ial has be5 9 use2 b ! g5]ally ackn[l$g$ belief1 q 9 agreem5t ) ! au?or's obs]vation1 t /eel ru/s m freely ?an wr\ght iron1 sugge/s t su* bridges w h a %ort] lease ( life1 ! m s t ! surface-to-section ratio is also great] = high] unit /resses1 ?\gh o!r adv]se influ5ces are mu* ! same = "o mat]ial z = ! o!r4 ,( ca/-iron /ructures b few cases h be5 giv52 ( ^!1 ca/-iron ar*es h be5 notic$ z develop+ defects :i* l$ to recon/ruction1 or to limit+ ! loads to be c>ri$4 ,pla9 ca/-iron gird]s1 on ! o!r h&1 h nev]1 "u ! au?or's direct obs]vation1 be5 remov$ = any o!r reason ?an because !y 7 ca/ iron1 or f ov]-/ress1 due to ! gr[? ( loads2 nev] f defects or wa/+1 ?\gh x is n sugge/$ no su* cases exi/4 ,! au?or has no evid5ce :i* po9ts to :at may be ! limit ( life ( a good ca/-iron gird] fairly treat$4 ,examples ( ,life ( ,metallic ,bridges4 ---------------------------------------- -------------------------- ,description4 ,span4 ,age4 ,defect4 ,ref]5ce4 ---------------------------------------- -------------------------- ft4 94,ye>s4 ,wr\ght ,iron4 ,plate gird]s 787 #ab ,loose rivets 99,ditto #ce #j #ab ,ditto p4 #eb ,ditto #ee #j #ad ,ru/4 ,di/ortionpp4 #gh #ig ,tr\gh gird]s #aa #j #af ,loose rivets4 p4 #ej ,crack$ webs ,plate gird]s 787 #bb ,loose rivets ,tw9 gird]s #ca #f #bc ,weak4 ,crack$ p4 #ac webs ,ditto #ce #f #bc ,weak4 ,di/ort$4p4 #gd ,plate gird]s #db #j #bc ,loose rivets4 p4 #ba ,crack$ webs ,ditto #gb #j #bi ,weak4 ,loose p4 #ec rivets ,ditto #dg #j #bd ,di/ortion p4 #i ,ditto #cb #j #cb ,ru/4 ,crack$ p4 #ad webs 99,ditto #be #j #cf ,weak p4 #fc ,/eel4 99,tr\gh gird]s #ae #h #cb ,weak4 ,ru/$ pp4 #fh #ih ,ca/ ,iron4 99,gird]s #cb #j #cf ,weak p4 #ada ,gird]s1 ca/-iron piles 787 #dd ,ditto ,ar*es #de #j #ee ,crack4 ,settle- p4 #ade m5t ,ditto #ajj #j #fb ,crack4 ,de=ma- pp4 #hj #ade tion ---------------------------------------- -------------------------- ,) timb] bridges ! l5g? ( life appe>s to be ab\t tw5ty-five ye>s1 b ?is is v l>gely dep5d5t ^u ! "q ( ma9t5ance1 & may range f fifte5 to ?irty-five ye>s4 ,x is manife/ t repairs1 :5 ext5sive & consi/+ ( ! r5ewal ( ! m ess5tial p>ts ( ! /ructure1 bord] ^u recon/ruction1 & may be cont9u$ indef9itely4 ,! l5g? ( life 9 ord9>y cases1 & = ! timb]s commonly us$ 9 ?is c\ntry1 may1 = railway bridges1 be tak5 z /at$1 ?\gh = highway bridges possibly long]4 ,( masonry bridges little is to be said b t x is only 9 cases ( bad "w or mat]ial--)1 p]haps1 vibration or settlem5t--t ^! h a %ortness ( life comp>able ) t ( defective metallic bridges4 ,:]e ^! adv]se conditions obta91 heavy repairs may be necess>y be=e ! /ructure is _m ye>s old2 b1 "u reasonably fair conditions1 bridges ( masonry may be expect$ to outla/ /ructures 9 any o!r mat]ial4 ,ap>t f road-bridges :i* are admitt$ly long-liv$1 !re are a l>ge numb] ( railway bridges & viaducts ( masonry :i*1 despite heavy loads & vibration1 h be5 9 use = ! pa/ sev5ty ye>s4 ,deal+ ) ! co/ ( ma9t5ance1 ?is ) bridges ( wr\ght iron or /eel %\ld result simply f scrap+ & pa9t+1 ) su* o!r incid5tal "w z may be necess>y on ! subsidi>y mat]ials us$ 9 ! /ructure4 ,! co/ ( pa9t+ w v>y ) ! height & "* ( ! bridge1 & ! am\nt ( scaffold+1 if any1 & may be f #e;d4 to #as4 or m p] squ>e y>d2 ?is if di/ribut$ ov] five ye>s1 a n unusual int]val betwe5 ea* pa9t+1 works out at an appreciable figure1 :i* may v>y f "o-?ird to "o p] c5t4 ( ! fir/ co/1 p] annum4 ,! ye>ly co/ ( pa9t+ /eel-"w w1 = %ort] int]vals1 come to a some:at high] figure4 ,s]i\s occasional items ( exp5se are ^? :i* %\ld n be necess>y1 repairs & possibly /r5g!n+1 :i* may raise ! total co/ ( ma9t5ance v consid]ably4 ,ca/-iron bridges1 be+ less liable to ru/1 co/ less = pa9t+ ?an o!r metallic bridges2 & if ! ca/ iron is clos$ 9 by masonry1 practically no?+2 !y d1 inde$1 involve v little exp5diture 9 ! ma9t5ance4 ,n be+ v am5able to repair or /r5g!n+1 ca/-iron bridges commonly rema9 v mu* z built1 or are recon/ruct$4 ,! prop] c>e ( timb] bridges may become co/ly z ! /ructure ga9s 9 age1 & soon gr[ to a v wa/eful exp5diture4 ,?is is evid5t :5 x is consid]$ t repairs may be necess>y aft] t5 ye>s1 & t :atev] may h be5 ! co/ ( any "p :5 new1 x _c be replac$ = ! same am\nt1 hav+ reg>d to ! lab\r exp5d$ 9 remov+ ! old memb]1 & ! special precautions to be obs]v$ 9 deal+ ) an old /ructure c>ry+ its load4 ,9 addition to ord9>y repairs1 !re w be pa9t or o!r protective coat+ to be appli$1 ?\gh ?is is n always done4 ,! upkeep *>ges ( masonry bridges w be practically no?+ 9 fav\rable cases2 b1 on ! o!r h&1 :]e ext5sive repairs become necess>y1 may rea* a consid]able am\nt4 ,exceptional outlays are1 h[ev]1 infrequ5t1 & may be spread ov] a l>ge numb] ( ye>s1 9 ^? r>e in/ances 9 :i* !y become imp]ative4 ,durability4 ,ma9t5ance ,fir/ ,co/4 ,*>ges4 ,masonry ,masonry ,timb] ,ca/ ,iron ,ca/ iron ,masonry ,wr\ght iron ,wr\ght iron ,/eel ,/eel ,/eel ,ca/ iron ,timb] ,timb] ,wr\ght iron ,= purposes ( ready comp>ison1 plac+ bridges ( ! mat]ials "u review 9 ord] ( durability1 !y w\ld appe> z 9 column #a ( ! table above2 9 ord] ( l[ ma9t5ance *>ges1 g5]ally z 9 column #b2 & 9 ord] ( l[ fir/ co/1 z 9 column #c4 ,) respect to ! "q ( fir/ co/1 ! arrangem5t ( ! ?ird column applies only to small bridges1 say1 up to #gj-;foot span2 &1 be+ liable to v>iation ) ! conditions1 is b approximately correct4 ,! less co/ly descriptions ( masonry are alone consid]$ 9 ?is connection4 ,x may be add$ t ! total ye>ly *>ge ( int]e/ on fir/ co/1 r$emption1 & ma9t5ance1 appe>s to be = masonry bridges1 ab\t "o-half only ( ! correspond+ totals = bridges ( wr\ght iron1 /eel1 or timb]2 ^? ( ca/ iron tak+ an int]m$iate place4 ,summ>is+ ! above consid]ations1 & deal+ ) ! relative m]its ( bridges 9 ! diff]5t mat]ials1 x may be broadly /at$ t = conditions at all suitable no?+ seems to be sup]ior to masonry--includ+ 9 ?is description fir/-class brickwork--:e!r = road or railway bridges4 ,"o pron\nc$ advantage ( su* bridges ) respect to l5g? ( life1 is t !y are b little affect$ by increase ( loads4 ,! mass ( a masonry ar*$ /ructure is s great1 & ! m>g9 ( /r5g? commonly s lib]al1 t consid]able increm5ts ( load may h b little effect ^u ! reliability ( ! /ructure4 ,ca/ iron has1 = bridges ( simple design1 a /rong claim to ! second place1 ?\gh its want ( ductility is a dem]it4 ,x c1 h[ev]1 h b a limit$ use 9 bridge con/ruction1 be+ applicable only to small gird] spans & skilfully-design$ ar*$ /ructures4 ,= bridges ( mod]ate span 9 :i* ! "q ( co/ does n control ! matt]1 wr\ght iron %\ld probably come next1 /eel be+ be/ res]v$ = ^? ( a l>g] size1 9 :i* weight ( ! /ructure greatly affects economy4 ,timb] may be reg>d$ z a mat]ial r>ely to be us$ 9 ?is c\ntry = /ructures to occupy a p]man5t place1 unless = urg5t economic reasons ( ! mom5t4 ,:ile express+ ?is g5]al view ( ! matt]1 x is to be admitt$ t ! propriety ( ^! conclusions is some:at disc\nt$ by ! difficulty !re n[ is 9 obta9+ ca/ iron ( ! desir$ t\ghness1 or wr\ght iron ) promptitude & suffici5t v>iety ( section at a reasonable price4 ,x is app>5t1 also1 t ! *oice ( mat]ial may be l>gely influ5c$--ev5 det]m9$--by consid]ations ( headway1 con/ruction dep?1 or "* ( f\ndations2 s t no v def9ite rules c be usefully laid d[n1 ?\gh ! adoption ( unsuitable mat]ials has n be5 s unusual z to make ^! sugge/ions altoge!r purposeless4 ,,*apt] ,,xvi4 ,,recon/ruction ,,& ,,wid5+--,,conclusion4 ,! ne$ = ! recon/ruction ( bridges1 aris+ f v>i\s causes :i* h be5 treat$ 9 ! prec$+ *apt]s1 orig9al weakness or faults 9 design1 decay or defects1 may also be caus$ by su* extrane\s consid]ations z ! gr[? ( loads1 wid5+ ( ! op5+s spann$1 or improvem5t ( ! headway4 ,9 any case1 a precise survey or measur+ up ( ! /ructure & its imm$iate surr\nd+s is requir$1 9 ! execution ( :i* ! greate/ c>e is desirable1 & ) respect to :i* x may be well to give a few h9ts4 ,! survey+ *a91 :5 us$1 %\ld be te/$1 ! measure ( accuracy requir$ r5d]+ ?is imp]ative 9 a degree peculi> to "w ( ?is class4 ,l95 tapes %\ld also be comp>$ ) a reliable /eel tape1 & us$ only :]e suffici5tly accurate = ! p>ticul> purpose4 ,a c>eful & obs]vant man may d v good "w ) a l95 tape1 mak+ j t all[ance 9 ! sag ( ! tape :i* corrects = ! inevitable /ret*2 b !re is /ill "s unc]ta9ty involv$ 9 its use1 & ! au?or pref]s to rely ^u a /eel tape1 not)/&+ ! inconv5i5ce commonly exp]i5c$ f its intractable nature & liability to damage4 ,in/rum5ts us$ mu/ also be 9 ! be/ adju/m5t2 z errors1 :i* 9 ord9>y field "w may n be ( great importance1 are inadmissible 9 bridge "w4 ,x is n necess>y "h to ent] ^u ! me?ods ( small survey "w1 b x may be desirable to po9t out t abutm5t walls %\ld be plumb$ = v]ticality2 gird]s1 :i* are liable to be lean+1 def9$ 9 position by ref]5ce to _! be>+s2 & g5]ally t x %\ld nev] be tak5 = grant$ t !re is tru? 9 old "w1 or t ?is may be assum$ z to l9e or level4 ,9 cases :]e disputes ) any local au?ority z to headway are likely to arise1 x is prud5t to supplem5t ! in=mation z to level ( s(fits by rods cut to l5g? 9 /rict agreem5t ) ! cle> height1 be=e remov+ ! old sup]/ructure4 ,x is app>5t t 9 cases :]e ! sup]/ructure is already condemn$1 ! detail measurem5ts may be conf9$ to t "p ( ! /ructure :i* is to rema91 secur+ only su* in=mation z to ! "w sup]s$$ :i* may be requir$ 9 arrang+ = ! new "w4 ,9 tak+ p>ticul>s ( skew bridges1 ne$less z ! w>n+ may seem1 x is yet necess>y to rem>k t !re may be "r or left-h& skews :i* w n rev]se4 ,! au?or has kn[n a disreg>d ( ?is to make s]i\s tr\ble 9 two in/ances4 ,deal+ fir/ ) recon/ruction ( ! sup]/ructure ( railway "u-bridges1 ^!1 if small1 may n give mu* tr\ble1 ?\gh ! dem& = great] /r5g? w1 p]haps1 involve "s difficulty 9 work+ to ! limit+ con/ruction dep?--i4e41 ! di/ance f ! top ( rail to s(fit ( bridge--p>ticul>ly z _m old bridges h a v nigg>dly all[ance 9 ?is respect4 ,x may be1 & q commonly is1 necess>y to raise ! rails a small am\nt1 or1 if headway is n re/rict$1 to l[] ! s(fit4 ,cle>ances betwe5 ! runn+ gauge & gird]-"w may also be difficult to secure1 m lib]al all[ances be+ n[ requir$ ?an =m]ly4 ,complications 9 ! "* ( ! p]man5t way1 s frequ5tly f\nd ^u old bridges1 %\ld1 ( c\rse1 be got rid (1 if possible2 b ! endeav\r may introduce fur!r difficulties4 ,reg>d mu/ ?r\gh\t be _h to ! me?ods to be adopt$ 9 remov+ old "w & 9 erect+ ! new4 ,p]haps ! simple/ case to deal ) is t :]e gird]s lie p>allel to1 & "u ! rails1 ) a timb] floor ^u :i* ! p]man5t way is c>ri$1 z sections ( ! road involv+ pairs ( gird]s may be readily remov$1 & replac$ by ! new gird]-"w 7see ,fig4 #ic74 ,if ! deck be ( tr\gh floor+ or old rails1 ! matt] may n be s simple1 z reg>d mu/ !n be _h to ! position ( jo9ts 9 ! exi/+ floor1 & ! new "w be s*em$ ) respect to ! numb] & (fice ( gird]s :i* may be got 9 at any "o break+ ( ! road4 ,a slight slew+ ( rails may sometimes be resort$ to on occasion1 :]e ?is has ! effect ( releas+ "s "p ( ! "w n o!rwise to be dealt )4 ,illu/ration3 ,,figs4 #ic & #id4 ,bridges hav+ ma9 gird]s1 ) timb] or tr\gh floor+ re/+ ^u ! bottom flanges1 or susp5d$ by bolts1 w1 if c>ry+ _m roads1 cause "s little difficulty1 z ! dismantl+ ( any "o span involves ! di/urbance ( o!rs2 :]e1 h[ev]1 _m l9es are conc]n$1 x may be feasible to put "o or m tempor>ily out ( use1 pres]v+ ! cont9uity ( traffic ov] ^? :i* rema91 b refra9+ f any div]sion ( ! m important roads4 ,some:at simil> tr\bles occur :]e ma9 gird]s ) cross-gird]s at ! l[] flanges are f\nd1 p>ticul>ly if ! cross-gird]s are arrang$ 9 l9e1 ! ends abutt+ on ea* side ( ! same ma9 gird] webs4 ,x is seldom1 h[ev]1 t ?is con/ruction is us$ 9 bridges ( small span c>ry+ _m roads2 b :]e x does occur1 x may necessitate ! use ( timb]+ bel[1 to c>ry ! ends ( cross-gird]s :5 fre$ f _! support+ ma9 gird]s4 7,see ,fig4 #id47 ,illu/ration3 ,,fig4 #ie4 ,if x is propos$ to use new ma9 & cross-gird]s1 x is desirable to arrange ^! 9 ! mann] already recomm5d$1 ! cross-gird]s n 9 l9e2 ?is has peculi> advantages 9 recon/ruction "w1 z ! bolt+ up & rivet+ ( ! cross-gird] ends is n hamp]$ by o!r cross-gird] atta*m5ts1 leav+ ea* piece ( floor complete 9 itself4 ,tw9 ma9 gird]s are occasionally us$ ) ! same object1 & pres5t ! advantage ( simplicity 9 erection & indep5d5ce ( "o span f ^? adjo9+ 7see ,fig4 #ie72 b ! me?od is wa/eful ( space1 & involves a some:at great] total weight 9 ! ma9 gird]s4 ,! =ego+ obs]vations apply m g5]ally to small s+le-span bridges1 ! op]ations on :i* may be effect$ )\t any mat]ial di/urbance ( traffic arrangem5ts2 ?\gh ?is c seldom be :olly avoid$1 x %\ld be conf9$1 :]e practicable1 to a few h\rs on a ,sunday4 ,! recon/ruction ( bridges ov] #gj-;feet span may h to be dealt ) "u m elaborate arrangem5ts1 if c>ry+ two l9es only1 possibly ) s+le-l9e work+ = a p]iod m or less protract$2 or x may be necess>y1 hav+ reg>d to ! weight ( ma9 gird]s to be remov$1 to c>ry ! :ole /ructure ^u tempor>y /ag+1 support+ ! road indep5d5tly1 cutt+ up & remov+ ! old "w1 & lat] putt+ ! new "w 9 place1 ei!r by detail$ erection 9 its ultimate position1 or by erection at "o side & draw+ across4 ,! latt] me?od is1 h[ev]1 commonly res]v$ = cases 9 :i* no special /ag+ is us$ "u ! old /ructure4 ,bridges ( a numb] ( op5+s are usually dealt ) by secur+ full possession ( "o road at a "t1 :i* = d\ble-l9e bridges necessitates s+le-l9e work+4 ,x is commonly out ( ! "q1 ev5 ) mod]ate spans1 to deal ) "s ( ^! only at a "t1 & s avoid cont9u\s possession ( "o road1 = a l5g!n$ p]iod2 & x c only1 z a rule1 be manag$ :]e ! ends ( ! new ma9 gird]s d n 9 any way int]f]e ) ^? ( ! old1 & :]e x is n necess>y to reset b$-/ones1 or make o!r alt]ations 9 ! be>+s :i* necessitate ! complete cle>ance ( ! pi]-tops4 ,9 exceptional cases x may be f\nd possible to arrange = ! complete removal ( a small numb] ( mod]ate spans on a ,sunday1 & ! putt+ 9 place ( ! new "w1 z 9 ! case ( small s+le spans4 ,spans erect$ to "o side ( ! f9al position1 to be lat] travell$ across1 are commonly m\nt$ ^u gantry /ag+1 & up to #ej tons weight may re/ directly ^u rails well greas$4 ,! p[] adopt$ to move ! span is usually t ( screw or hydraulic jacks1 or occasionally eng9e haulage1 special tackle be+ 9 t case necess>y to apply ! eng9e p[] 9 ! "r direction4 ,if ! "t is limit$1 or weight consid]able1 a m elaborate arrangem5t by :i* ! load is support$ ^u :eels1 may be necess>y1 ) a view to r$uc+ ! resi/ance to a manageable am\nt4 ,all "w :i* x is possible to d be=e %ift+ into place1 includ+ ! p]man5t way1 :]e ?is is ( a special "*1 %\ld be execut$ 9 advance1 leav+ only ! rail connections to be made good :5 ! span is 9 position4 ,:]e timb] /ag+ is us$ to c>ry ! p]man5t way be=e dismantl+ an old /ructure1 x is conv5i5t to beg9 by plac+ /\t balks ( timb] "u ! sleep]s f end to end ( ! bridge1 or directly "u ! rails if space is limit$2 ! /ag+ is !n arrang$ to give support to ! runn+ timb]s4 ,metallic "u-bridges ( ample headway1 p]haps ov] coal-work+s 7s9ce settl$ d[n71 or = "s less suffici5t reason made ( metal1 may be *eaply replac$ by brick ar*es built bel[ ! old sup]/ructure1 ! spr++s ( ! ar* be+ *eck$ into ! face ( ! exi/+ abutm5ts4 ,) /\t walls1 c>eful "w & good mat]ial w make ?is an effici5t & durable job4 ,x be+ a prim>y condition ( recon/ruction "w to int]f]e b little ) ord9>y traffic arrangem5ts1 s+le-l9e work+ is avoid$ :]ev] practicable2 z ?is1 always objectionable1 may necessitate ! erection ( special signals & signal app>atus1 besides ! tempor>y remodell+ ( ! roads1 & 9 ?is c\ntry may involve also a ,bo>d ( ,trade inspection--altoge!r a tr\blesome & exp5sive bus9ess4 ,any bridgework :i* is accompani$ by break+ or block+ ! road c only be und]tak5 by arrangem5t ) ! traffic dep>tm5t1 aft] notice duly giv5 & publi%$ 9 ! p]iodical record ( su* matt]s2 x is g5]ally fix$ = a ,sunday4 ,prep>atory to ?is1 x is necess>y to make all ready by gett+ z mu* done be=eh& z is possible4 ,:]ev] practicable & prud5t1 ! :ole "w is releas$ f its surr\nd+s1 masonry cut away1 rivets cut out & replac$ by good bolts1 nuts remov$ f hold+ d[n bolts1 or ! bolts cut ?r\gh1 etc4 ,p>ticul> c>e %\ld be ex]cis$ to asc]ta9 :at rema9s to be done imm$iately prior to removal4 ,x is necess>y fur!r to arrange = trucks to be 9 read9ess to receive old mat]ial1 & o!rs conta9+ new gird] "w to be conv5i5tly /ation$1 hav+ be5 load$ up to come "r end =emo/2 eng9e p[]1 cranes1 empty & load$ trucks1 be+ all m>%all$ & s plac$ z to be available 9 prop] ord]1 & z want$4 ,!re mu/ be no mi/ake z to :at roads w be f\l$ by sw++ ! crane ) its load1 or z to ! rea* ( ! crane 9 effect+ its "w4 ,! :ole op]ation to be conduct$ on any ,sunday %\ld be well )9 ! res\rces ( ! m5 & plant engag$ 9 x1 or s manag$ t x is a matt] ( no s]i\s importance if ! :ole _c be complet$ z orig9ally desir$4 ,possession ( ! roads to be block$ hav+ be5 secur$ betwe5 c]ta9 h\rs1 if "s "p only ( ! "w to be c>ri$ out has be5 complet$ z ! "t gr[s %ort1 any attempt to execute ! rema9d] may result 9 *eck+ tra9s until su* "t z ! l9e may be report$ cle>--a cont+5cy to be avoid$--?\gh ! temptation to save ano!r ,sunday's "w by delay ( a few m9utes to "s "o tra9 may be consid]able4 ,9 s*em+ any recon/ruction1 x may be insi/$ t at lea/ "o feasible me?od ( c>ry+ out ! "w mu/ be secur$1 ?\gh x is ! au?or's exp]i5ce t frequ5tly "s o!r me?od ?an t contemplat$ is 9 ! end adopt$1 :51 "s mon?s lat]1 ! f9al arrangem5ts = fix+ are made4 ,! t5d5cy ( a zeal\s erector is commonly to take full advantage ( any facilities (f]$1 ) a view to a mod]ate am\nt ( "w be+ done at any "o "t1 & to a*ieve z mu* m z he c himself secure by s*em+1 or a lib]al use ( lab\r2 all ,sunday "w1 ) att5dance ( eng9es & cranes1 be+ ( necessity exp5sive4 ,railway ov]-bridges d n commonly pres5t any p>ticul> difficulties4 ,! spans to be dealt ) are usually small1 & ! weights to be lift$ mod]ate4 ,! height above rails may1 h[ev]1 be above ! lift ( any crane2 &1 = ! purpose ( rais+ ma9 gird]s1 a d]rick may become necess>y1 ! re>+ & guy+ ( :i* may block _m roads dur+ ! "t x is 9 use4 ,! gird]s ( l>g] spans1 too unmanageable to be lift$ :ole1 may be erect$ ^u /ag+2 to secure ! requisite headway x may be necess>y to build ! gird]s at a level above t at :i* !y w f9ally be1 l[]+ !m into position :5 self-support+1 & aft] ! removal ( ! /ag+4 ,! wid5+ ( railway "u-bridges is1 z a rule1 a matt] ( no special difficulty1 b "s rem>ks may be ( use4 ,wid5+s %\ld be plann$ ) a reg>d to lat] recon/ruction ( ! orig9al bridge1 if t is at all likely to be necess>y1 & ) ! object t1 :5 complete1 ! :ole %\ld be a consi/5t piece ( "w4 ,x may1 inde$1 happ5 t wid5+ ( a bridge may involve ! remodell+ or recon/ruction ( ! old "w1 to enable ! new roads to be laid d[n z desir$2 ?is is m likely to be necess>y :]e !re exi/ ma9 gird]s n compet5t to take any additional load1 & to duplicate :i* w\ld sacrifice space betwe5 ! new & old roads2 or x may be unavoidable because ( slew+ ( ! old rails1 z "p ( a g5]al re>rangem5t4 ,illu/ration3 ,,fig4 #if4 ,deal+ ) wid5+s simply1 !re is (t5 "s little tr\ble 9 contriv+ a connection betwe5 ! new & ! old "w1 z ?is may h to be made "u1 or close to1 ! sleep] ends ( ! exi/+ roads4 ,x is desirable to arrange ?is "p s t no drill+ ( old "w = rivets or bolts %all be necess>y1 !re be+1 9 fact1 no /rict connection4 ,by judici\s s*em+1 ?is may be effect$1 :il/ secur+ fre$om f leakage ( wat] at ! jo9t4 7,see ,figs4 #if & #ig47 ,if ty+ ( ! new & old /ructure is desir$1 ?is c usually be done q simply1 well bel[ ! floor at "s m accessible level4 ,illu/ration3 ,,figs4 #ig & #ih4 ,! /rict jo9t+-up ( tr\gh floor+1 new to old1 at "r angles to ! tr\ghs1 _c be contemplat$1 b may be dealt ) by treat+ ea* "p indep5d5tly1 ! ends be+ ne> toge!r1 sep>at$ by ! space ( an in* or s4 ,ea* tr\gh end be+ clos$ up by a diaphragm or oak block to prev5t balla/ dropp+ ?r\gh1 ! top ( ! space may be cov]$ by a loose /rip1 secur$ to prev5t x %ift+1 ! bottom provid$ ) a gutt] ( lib]al dim5sions to take away leakage1 z x is practically impossible to make ?is arrangem5t 8drop dry0 "u ! conditions common 9 execut+ "w ( ?is k9d 7see ,fig4 #ih74 ,illu/ration3 ,,figs4 #ii & #ajj4 ,:]e tr\gh floor+1 new & old1 has to be made good p>allel to ! tr\ghs1 ! difficulty ( mak+ a direct connection is less m>k$1 & x is n unusual to introduce a /rip cov] simply2 b if accessible1 ! "w is /ill tr\blesome1 z !re is commonly a want ( /rict alignm5t & tru? z to level1 betwe5 ! new & ! old tr\ghs4 ,x is pref]able to arrange = junctions ( a m conv5i5t type1 z 9 ,figs4 #ii & #ajj4 ,:5 wid5+ masonry ar* bridges by gird]-"w1 x is desirable to insure t any gird]s p>allel to ! masonry face %all be suffici5tly f> remov$ f x to enable pa9t+ to be execut$4 ,! space rema9+ betwe5 ! gird] & ! ar* may !n be bridg$ by floor-plates1 or an ext5sion ( ! timb] floor if t is adopt$4 ,9 effect+ a junction su* z ?is1 ! au?or has us$ ! arrangem5t %[n 9 ,fig4 #aja1 ! advantage be+ t ! piece ( connect+-floor is suffici5tly wide1 & also suffici5tly flexible1 to all[ ! gird]-"w fre$om to deflect )\t do+ h>m4 ,! load c>ri$ by ! wid? ( floor is1 z to "o "p1 deliv]$ well on to ! old masonry1 9 pref]5ce to be+ impos$ ne> to ! face4 ,if x %\ld = any reason be imp]ative to place ! gird] close to ! ar* face1 x is pref]able to s*eme ! floor s t !re %all be no actual contact1 ! new floor 9 t case slightly ov]hang+ ! masonry1 z 9 ,fig4 #ajb1 or dealt ) z 9 ,fig4 #ajc1 if dep? is re/rict$4 ,! wid5+ ( masonry ar* bridges by masonry1 calls = no o!r rem>k ?an t ! new "w %\ld be free f ! old2 ?\gh x may be advisable1 :5 ! wid5+ is n>r[1 to tie ! new "w to ! old 9 su* a way z to p]mit indep5d5t settlem5t4 ,if ! wid5+ is exceptionally n>r[1 !re may be no *oice b to bond ! new & old "w toge!r1 & 9 ! be/ mann]1 ) ! object ( m9imis+ ! risk ( sep>ation4 ,illu/ration3 ,,figs4 #aja & #ajb4 ,illu/ration3 ,,fig4 #ajc4 ,! above matt]s relative to wid5+s1 ?\gh app>5tly trifl+1 may by neglect cause mu* tr\ble & exp5se 9 ma9t5ance4 ,!y pr9cipally conc]n small bridges1 ! ext5sion ( l>g] /ructures com+ r 9 ! category ( indep5d5t works4 ,,conclusion4 ,9 br++ ^! *apt]s1 deal+ l>gely ) que/ions affect+ ma9t5ance1 to a close1 x may be well to draw att5tion to ! fact t economy 9 design 7ap>t f improp] r$uction ( sections7 goes h&-9-h& ) economy ( upkeep4 ,giv5 good mat]ial1 t :i* fav\rs l[ fir/ co/1 simplicity ( detail1 fewness ( p>ts1 abs5ce ( smi?+1 ! use ( roll$ sections1 & good dep? to gird]s1 fav\rs also small exp5diture 9 ma9t5ance4 ,! less complex ! design1 ! easi] w x be to keep ! /ructure 9 ord]2 ! less ! numb] ( p>ts1 ! few] w be ! connections4 ,fre$om f smi?+ elim9ates liability to failure at cranks1 or o!r "w :i* has be5 subject to fire4 ,x is app>5t also t ! free use ( roll$ in/ead ( built-up sections1 r$uces ! liability to tr\ble f bad rivet+1 or f good rivet+ ov]/ress$4 ,a lib]al dep? to all gird]s1 by r$uc+ deflections1 limits ! incl9ation ( ! ends & gives ! connections a bett] *ance ( rema9+ intact4 ,la/ly1 ) "w ( ?is "*1 ! lab\r ( scrap+ & pa9t+ is simplifi$ & *eap5$4 ,! au?or wi%es to reit]ate ! /atem5t made 9 ! op5+ p>agraphs ( ?is book1 t all in/ances ( decrepitude1 failure1 or peculi> behavi\r cit$1 h be5 "u 8 direct obs]vation4 ,! fact is insi/$ ^u simply t ! read] may appreciate t ! in=mation is at fir/ h&4 ,x has n be5 ?\ght necess>y1 nor 0 x consid]$ desirable1 to indicate ! locality ( ea* case ref]r$ to2 b x may be said t ! matt] ( ^! *apt]s has be5 accumulat+ dur+ _m ye>s1 & relates to /ructures "u ! control ( _m diff]5t bodies4 ,! /udy ( old bridges is /rongly recomm5d$1 p>ticul>ly ) respect to /ress & /ra91 :i* 9 /ructures new or old1 occur possibly z may be expect$--c]ta9ly z !y mu/4 ,consid]ation ( exi/+ "w may ?us be a useful *eck ^u ! fanciful requirem5ts ( "s me?ods ( design4 ,!re is a rec5t t5d5cy1 = in/ance1 9 ,engli% practice to ov]-/iff5 ! webs ( plate-gird]s1 su* t if ! !ory ^u :i* ! results are bas$ 7 true1 _m old bridges c>ry+ _! loads ) no sign ( di/ress1 %\ld h fail$ long ago4 ,excess 9 rivet+ is a common extravagance1 to :i* ! same criticism may 9 a less degree apply4 ,consid]able impact all[ances = gird]s ( l>ge span may also be ref]r$ to z an application ( empiric !ory n ju/ifi$ by exp]i5ce1 :i*1 z 9 all cases :]e su* consid]ations fight ) facts1 %\ld be modifi$ or reject$4 ,,index ,abutm5ts1 lean+1 #hb1 #agc -- movem5ts (1 #aeh -- settlem5t (1 #gh ,adju/m5t ( c5tre gird]s1 #abh -- ( di/ribut+ gird]s1 #abj ,angul> di/ortions1 #hh ,ar*es1 equilibrium (1 #afb -- repair (1 #afc ,arrangem5t ( cross gird]s1 #ba1 #age ,asphalt1 #bf ,balla/1 #bi ,be>+ pressure on rivets1 #dg1 #ea1 #eg ,be>+s1 skew1 #d ,bottom booms1 end bays1 #ah ,brac+1 additional1 #aag -- effects (1 #cd -- flat b>s1 #cg -- incomplete1 #da -- sea pi]s1 #db ,bridge floors1 #bj -- repairs1 #ajg -- surveys1 #ajg ,bridges1 life (1 #afe ,breaks 9 ,t b>s1 #af ,buckl+ ( webs1 #af ,camb]1 #bd1 #hj ,ca/-iron ar*es1 #hj1 #ade -- -- bridges1 #ada -- -- columns1 #g1add -- -- gird]s1 #ada -- -- 9 sea wat]1 #aja ,c5tre gird]s1 #abb ,c9d] balla/1 #bi ,cold-bla/ iron1 #ada ,cool+ /resses 9 ca/ iron1 #ade ,con/ruction dep?1 #agc ,corrugat$ %eet+1 #bi ,co/ ( c5tre gird]s1 #ace -- ( ma9t5ance1 #afh ,c\nt]brac+1 #ai ,crack$ b$/ones1 #c -- columns1 #g -- web plates1 #ac1 #ad1 #ae1 #ej ,cross gird] arrangem5t1 #ba -- gird]s1 fix$ ends1 #bb1 #aah -- -- ru/$1 #bi1 #ig -- -- weak1 #cj1 #ff ,decay & pa9t+1 #if -- ( floor plates1 #aji -- ( timb]1 #bh1 #aej ,deflection1 #he -- due to booms & web1 #hf -- exceptional cases1 #hh -- 9 new & old "w1 #he -- work+ =mul1 #hg ,de=mations1 #gc ,dep? ( gird]s1 #bc1 #hi1 #ahd ,diagonal ties1 #ai1 #db ,di/ortion due to temp]ature *anges1 #gi1 #hd ,di/ribut+ gird]s1 #abj ,dra9age holes1 #be 8,drop0 loads1 #hi ,dw>f walls "u floors1 #bf ,e>ly /eel gird]s1 #fh ,economy1 #ahd ,effect ( e>? slips1 #aeg -- ( floor on deflection1 #hh -- -- -- on /resses1 #bc1 #cj -- ( high /ress1 #hf -- ( p]man5t way on /resses1 #ah --( skew on bridge floors1 #be -- -- -- on c5tre gird]s1 #aca -- ( transv]se brac+s1 #cd -- ( vibration on masonry1 #afb -- ( wave action on sea pi]s1 #db ,end bays1 bottom booms1 #ah ,equilibrium ( masonry ar*es1 #afb ,exam9ation ( bridges1 #ajg ,examples ( ca/-iron bridges ov]/ress$1 #ada -- ( high /ress1 #gj -- ( life ( bridges1 #afg -- ( rivet /ress1 #ef -- ( /r5g!n+1 #aad -- -- -- by c5tre gird]s1 #aca1 #acd ,excessive be>+ pressure1 #ea ,faulty workman%ip1 #hj ,fix$ ends to cross gird]s1 #bb1 #aah ,flange /resses1 #fc1 #ff1 #fg ,flanges1 side load$1 #i1 #gc ,flat b> brac+1 #cg ,flex+ ( gird]s1 #i1 #gd1 #gf ,flexure curves1 #ach ,fractur$ b$/ones1 #c -- rails1 #cj -- webs1 #ac1 #ad1 #ae1 #ej ,fractures 9 ca/ iron1 #g1 #ade ,gird] be>+s1 #b ,gird]s on columns1 #g -- on masonry1 #h ,gird]work 9 masonry1 #aja ,headway1 #agc ,high /ress1 #fa -- 9 ca/ iron1 #ada -- 9 rivets1 #dg1 #eb ,holes = dra9age1 #be ,impact1 #bj1 #fb ,incl9ation ( gird] ends1 #bc1 #ec ,incomplete brac+1 #da ,initial set1 #hh ,int]f]5ce ) traffic1 #agg ,jack ar*es1 #bi1 #aja ,jo9ts 9 rails1 #bi1 #aji -- 9 tr\gh floors1 #bh1 #ahj ,junction betwe5 metallic & masonry bridges1 #ahc -- -- new & old masonry bridges1 #ahb -- -- new & old metallic bridges1 #ahj ,lattice gird] /resses1 #dg-ff ,lib]al dep? to gird]s1 #bc1 #hi1 #ahd ,life ( bridges1 #afe ,limit ( ela/icity1 #fa ,l95 tapes1 #agb ,longitud9al floor gird]s1 #bc ,loose rivets1 #ba1 #be1 #ea1 #ec1 #ef1 #aji ,ma9 gird]s1 #i-ag ,masonry bridges1 #aeg -- endur+ "* (1 #afa ,memel timb]1 #aej ,me?ods ( calculation1 #df1 #fa -- ( obs]v+ deflection1 #ij -- ( sett+ out deflection curves1 #ach ,movem5ts ( abutm5ts1 #aeh -- ( ca/-iron bridge1 #hb -- ( pi]s1 #db1 #hc1 #aei -- ( roll]s1 #g -- ( wr\ght-iron bridges1 #d1 #ba1 #ch1 #gc ,new memb]s to old "w1 #aaf ,oil+ /eelwork1 #ii ,old draw+s unreliable1 #ajh -- rivets1 #ba1 #ea1 #ed1 #ee ,op5 webs1 #ag ,ov]head brac+1 #ci -- gird]s1 #aah ,pa9t+1 #ih ,p>apets1 #gi ,p]missible /ress 9 old "w1 #aaj ,pi]s1 movem5ts (1 #db1 #hc1 #aei -- out ( plumb1 #aei ,piles1 decay (1 #ajb1 #aej ,pit* p9e1 #bh ,pla/icity1 #fa ,plate webs1 #i ,plat$ floors1 #bc1 #be1 #cj ,po9t+ masonry1 #afd ,propos$ rivet /resses1 #eh ,quickly appli$ loads1 #hi ,rail jo9ts1 #bi1 #aji ,rails1 breaks 91 #cj ,reaction ( cross gird] ) c5tre support1 #abg ,r$-lead1 #ih1 #ajj ,relative m]its ( bridges1 #afi ,relief by c5tre gird]s1 #abb ,repa9t+1 #ajj ,repair ( bridges1 #ajg1 #adg1 #aee1 #afc -- ( timb] piles1 #aef ,replac+ flange plates1 #aaj -- rivets1 #aaa ,resi/ance ( ca/ iron to ru/1 #aja ,rivet$ connections1 #de1 #hf ,rivets 9 cramp$ positions1 #bj -- 9 cross gird] ends1 #ba1 #di1 #ec1 #ed -- 9 road bridges1 #fj -- 9 webs ( ma9 gird]s1 #df -- spac+ (1 #fj1 #hj -- /resses 91 #ef ,rock+ ( pi]s1 #h1 #hc1 #aei ,roll] be>+s1 #g ,rubble masonry1 #afa-afd ,runn+ load & deflection1 #ie ,ru/+1 in/ances (1 #bi1 #if -- ( /eelwork1 #ii -- ov] sea-wat]1 #ih ,sag 9 timb] bridges1 #aej -- ( tapes1 #agb ,sc\r "u pi]s1 #afa ,sea pi]s1 #db1 #ajb ,sett+ b$/ones1 #c1 #abi1 #agf ,settlem5ts1 #gf1 #aeg ,skew be>+s1 #d -- bridges1 "r & left1 #agc -- -- floors1 #be ,skirt+ plate1 #bf ,slope ( gird] ends1 #ib ,s(t5+ ( ca/-iron 9 sea-wat]1 #aja ,spac+ ( rivets1 #fj1 #gi ,spread ( abutm5ts1 #aeg ,spr+ jo9ts1 #bc ,/eel tr\gh gird]s1 #fh -- tr\gh+1 #gj ,/iff5+ gird]s f floor1 #ab1 #dj -- to webs1 #af1 #ch1 #ahe ,/op pi]s1 #aeh ,/r5g? ( light top booms1 #dj ,/r5g!n+ ( bridges1 #ajg1 #abb -- bridge floors1 #aah -- cross gird]s1 #abc ,/ress 9 plat$ floors1 #ca ,/udy ( old bridges1 #ahe ,tall pi]s1 #db1 #aei ,timb] bridges1 #adi -- floors1 #bg -- /ag+1 #agg ,top booms1 #ah ,traffic dur+ recon/ruction1 #agg ,transv]se brac+1 #cd1 #aag ,tr\gh floors1 #bg1 #ahj -- gird]s1 #ej1 #gd ,t /iff5]s1 breaks 91 #af ,tw9 gird]s1 #ae1 #ge ,twi/+ ( gird]s1 #aa1 #fh1 #gc -- -- -- correct$1 #ab ,types ( recon/ruction1 #agd ,u-%ap$ booms1 #ah ,uncomplicat$ /ress1 #fb ,uni=m pressure on be>+s1 #f ,value ( ,e 9 deflection =mul1 #hg ,vibration1 #afb ,wa/$ webs1 #ad1 #bi1 #if ,wat]1 sc\r (1 #afa ,web buckl+1 #af -- plates1 crack$1 #ac1 #ad1 #ae1 #ej -- rivets1 #df1 #ej -- /iff5+1 #af1 #ch1 #ahe ,wid5+ masonry bridges1 #ahb -- metallic bridges1 #agi ,wide spac$ rivets1 #gi ,w9d pressure1 #da1 #dc ,yield+ ( pi]s1 #h1 #hc1 #aei ,,london3 ,,pr9t$ ,,by ,,william ,,cl[es ,,& ,,sons1 ,,limit$1 ,,great ,,w9dmill ,,/reet1 ,w41 ,,& ,,duke ,,/reet1 ,,/am=d ,,/reet1 ,s4,e4 ,transcrib]'s ,notes3 ,! text ( ! orig9al "w 7includ+ inconsi/5t spell+1 hyph5ation1 =matt+ etc47 has be5 reta9$1 except z m5tion$ bel[4 ,! slight diff]5ces betwe5 ! ,table ( ,cont5ts & ! text h n be5 *ang$4 ,*anges made to ! text3 ,"s punctuation errors & obvi\s typographical errors h be5 correct$ sil5tly4 ,sev]al illu/rations h be5 mov$ to :]e !y are describ$ 9 ! text4 ,page #abc1 =mula 7#b73 ! orig9al %[s an uncle> sup]script aft] ! fir/ ,l4 ,z describ$ 9 ! foll[+ l9e ( ! text1 ?is has be5 *ang$ to ,ll4