AASHTO Load Ratings-3 & Looking to LRFR

7/26/2019 AASHTO Load Ratings-3 & Looking to LRFR

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AASHTO Load Ratings & LRFD

Looking to Load and Resistance Factor Rating

The LRFR process aims to improve the reliability of bridges and increasepublic safety.

On December 15, 1967, the Silver Bridge, carrying U.S. 35 between PintPlea!ant, "#, and $alli%li!, O&, clla%!ed, 'illing (6 %e%le and in)*ring 9when 31 + the 37 vehicle! n the bridge either +ell int the Ohi iver rnt it! !hreline. -nve!tigatin! later revealed that a crac'ed eyebarcreated *nd*e !tre!! n the ther bridge member!, leading t the clla%!e.

These inspectors are using a truck-mounted boom to collect data neededto determine the bridges loadcarrying capacity.

he incident %rm%ted natinal cncern ab*t bridge cnditin! and led tthe e!tabli!hment + the /atinal Bridge -n!%ectin Standard! 0/B-S in theearly 1972!. Since then, the ederal &ighway 4dmini!tratin 0&"4, the4merican 4!!ciatin + State &ighway and ran!%rtatin Ocial!044S&O, and ther! have wr'ed t im%rve !tandard! +r maintaining and


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in!%ecting ei!ting bridge!. he late!t ma)r ert in thi! area i! thedevel%ment + the lad and re!i!tance +actr rating 08 methd. -n 22144S&O ad%ted a new Guide Manual for Condition Evaluation and Load andResistance Factor Rating (LRFR of !igh"ay #ridges. he g*ide man*alre:ect! the m!t c*rrent technlgie! and b*ild! n the !tr*ct*ral reliability

a%%rach inherent in !%eci;catin! +r lad and re!i!tance +actr de!ign08D.

These inspectors are using a truck-mounted boom to collect data needed todetermine the bridges load carrying

capacity.

4ll State! are wr'ing t im%lement 8D +*lly by Octber 227, a! decidedby 44S&O and agreed *%n by &"4. 4! State! ad%t 8D acr!! thec*ntry, bridge %r+e!!inal! are recgni*r%e.Ba!ed n +actr! calibrated +rm !tr*ct*ral lad and re!i!tance !tati!tic!, the8D !%eci;catin! en!*re a mre *ni+rm level + %*blic !a+ety andreliability in newly de!igned bridge!. Ultimately, bridge engineer! e%ect thatthe 8D?8 a%%rach will hel% red*ce maintenance and re%air, avid


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c!tly vercn!ervative de!ign! and rating!, and re!*lt in a mre *ni+rmlevel + %*blic !a+ety n bridge! in the United State!.

Permit load rating calculations resultedin the safe transport of this truck, whichexceeded the States legal load and sizelimit.

!er!iew of "oad #ating

Bridge de!ign and lad rating are !imilar in verall a%%rach@ hwever, theydier in ne cr*cial a!%ect. -n de!ign, engineer! cntend with greater*ncertainty in the am*nt + lading the !tr*ct*re will e%erience ver it!!ervice li+e. "ith lad rating +r an ei!ting !tr*ct*re, n the ther hand,bridge engineer! +ace *ncertainty in the am*nt + !tr*ct*ral re!i!tance.

-n general, lad rating invlve! determining the !a+e carrying ca%acity.Bridge wner! %er+rm three ty%e! + lad ratingA de!ign, legal, and %ermit.De!ign and legal lad rating invlve the analy!i! + r*tine lad! that arewithin the legal limit!. Permit lad rating i! the analy!i! + !%eci;c vehicle!that carry lad! that are heavier than the legal limit.

Bridge wner! %er+rm lad rating! +r three main rea!n!A

1. dern bridge! generally are cn!tr*cted t la!t at lea!t 52 year!, and!me even lnger. >ven with %r%er maintenance, hwever, thecnditin + a bridge inevitably will deterirate t !me etent ver it!


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li+etime. hi! deteriratin c*ld lead t a red*ctin in the !trength rlad carrying ca%acity + the bridge. en!*re that all %*blic bridge!remain !a+e *nder c*rrent trac lad!, ladCrating analy!e! m*!t be%er+rmed when bridge cnditin! deterirate. 4ccrding t the /B-S,wner! need t cllect cnditin data +r all %*blic bridge! n a (C

mnth cycle.

. Bridge! in the c*rrent inventry were de!igned *!ing a variety +cn;g*ratin! +r live tr*c'lad!, de%ending n the de!ign!%eci;catin! at the time the bridge wa! b*ilt. 4! de!ign and rating!%eci;catin! evlve, new 'nwledge + act*al lading, behavir, andre!i!tance are incr%rated. here+re, regardle!! + the de!ignmethd! *!ed, all bridge! !h*ld be lad rated *!ing c*rrent traccnditin! and the late!t !tandard!, whenever %racticable, t en!*rethe !a+ety + the mtring %*blic.

3. 8a!tly, a %ermit lad rating i! nece!!ary +r vehicle! carrying lad!ver the legal limit. D*e t increa!ing demand! n the tr*c'ingind*!try, the vl*me + re*e!t! +r %ermit lad rating! cntin*e! tri!e, accrding t the B*rea* + ran!%rtatin Stati!tic!. &eavy r+re*ent %ermit lad! can red*ce a bridgeE! li+e r ca*!e %ermanent!tr*ct*ral damage i+ nt a!!e!!ed %r%erly.

r lad rating, re!*lt! are generally e%re!!ed in term! + a rating +actr +ra %artic*lar live lad mdel. ating +actr! greater than ne indicate that thebridge i! !a+e +r the lad! te!ted. =*rrently there are three methd!available +r lad rating bridge!A allwable !tre!! rating, lad +actr rating,

and 8.

$istorical %ackground f "oad #ating

-n the 1952! and 1962!, cn!tr*ctin + the U.S. inter!tate !y!tem and Statehighway !y!tem! wa! %rgre!!ing at an etrardinary rate. 4ccrding tthe #ridge $nspector%s Reference Manual 0&"4C/&-C23C221, a%%rimately115,222 %*blic bridge! in the United State! were de!igned and b*ilt between1961 and 1972. D*ring thi! time, highway cial! %laced little em%ha!i! n!a+ety in!%ectin! and maintenance + in!ervice bridge!.

4+ter the clla%!e + the Silver Bridge in "e!t #irginia in 1967, the U.S.=ngre!! re!%nded t the %*blic *tcry by directing the !ecretary +tran!%rtatin t e!tabli!h natinal !tandard! +r bridge in!%ectin. -n 1971,when the /B-S wa! created, they nly a%%lied t bridge! n the ederalC4id&ighway Sy!tem 0generally bridge! n any inter!tate, U.S r*te, r Stater*te !y!tem. 8ater, in 19F2, &"4 etended the !tandard! t cver all%*blic bridge! mre than 6 meter! 02 +eet in length. he /B-S e!tabli!hed a


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natinal %licy n in!%ectin %rced*re!, +re*ency, %er!nnel *ali;catin!,re%rt!, and maintenance + the /atinal Bridge -nventry 0/B-.

hree detailed man*al! !n were devel%ed t !*%%rt the /B-SA

he &"4 #ridge $nspector%s Training Manual, relea!ed in 1972 0nwthe Bridge -n!%ectrE! e+erence an*al

he 44S&O Manual for Maintenance $nspection of #ridges, relea!ed in1972

he &"4 Recording and Coding Guide for the &tructure $nventory and'ppraisal of the ation%s #ridges, relea!ed in 197

he /B-S e!tabli!hed directive! nt nly +r in!%ecting bridge! b*t al! +reval*ating and analy


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cmm*nity identi;ed a n*mber + !hrtcming! in the !%eci;catin!. ream%le, in!%ectr! arrived at a wide range + re!*lt! +r lad rating! n!imilar bridge!. 44S&O cial! determined that the di!%aritie! were mainlyd*e t variatin in inter%retatin + the lad rating !%eci;catin!.

im%rve the %rced*re!, in 19F9 44S&O relea!ed the Guide&peci)cations for &trength Evaluation of E*isting &teel and Concrete #ridges,%rviding the ;r!t ver!in + the 8 %rced*re!. By *!ing the !a+etyreliability a%%rach *tlined in the g*ide, engineer! +*nd that the ladcalc*latin re!*lt! were mre cnvergent. he g*ide !%eci;catin al!%rvided the %tin + *!ing !iteC!%eci;c trac in+rmatin and the!tr*ct*ral behavir hi!try + the bridge t arrive at mre acc*rate re!*lt!. 4tthat time, hwever, State de%artment! + tran!%rtatin 0DO! were !till*!ing lad +actr de!ign r allwable !tre!! de!ign, ! ad%ting 8 wa! ntan attractive %tin +r many State!.

-n 199(, 44S&O %*bli!hed the Manual for Condition Evaluation of #ridges toreplace the Manual for Maintenance $nspection of #ridges. 4lth*gh the newman*al cntained !me g*idance +r allwable !tre!! rating, it clearlyem%ha!i


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!ectin! n +atig*e eval*atin and nnde!tr*ctive te!ting are amng !me +the ther enhancement!. 4! with the earlier g*ide !%eci;catin!, the newman*al a%%lie! !tateC+CtheCart technlgy and allw! the *!e + !iteC!%eci;ctrac and !tr*ct*ral behavir cnditin!.

4! nted in /=&P "eb Dc*ment F 0Pr)ect =1C(6A =ntractrE! inale%rtA Manual for Condition Evaluation and Load Rating of !igh"ay #ridgessing Load and Resistance Factor /hilosophy, the 8 methd! %re!entedin the 223 man*al Gcntain the nece!!ary ingredient! t %rvide a mreratinal, a mre :eible, and mre %wer+*l eval*atin !trategy +r ei!tingbridge!.H

"oad &actor #ating

he lad +actr rating methd rate! bridge! at tw level!A inventry and%erating. he inventoryrating level crre!%nd! t c*!tmary de!ignCty%e

lad! while re:ecting the ei!ting cnditin + the !tr*ct*re.he operatingrating level crre!%nd! t the maim*m %ermi!!ible live ladthe !tr*ct*re can with!tand !a+ely. *rther, the inventry lad ratingaccmmdate! live lad! that a bridge can carry +r an inde;nite %erid,while the %erating lad rating re+er! t live lad! that c*ld %tentially!hrten the bridge li+e i+ a%%lied n a r*tine ba!i!.

4! !tated in the 44S&O Manual for Condition Evaluation of #ridges, thegeneral e%re!!in *!ed in lad +actr rating calc*latin! i! a! +llw!A

-n the e*atin, i! the rating +actr +r liveClad carrying ca%acity, = i! theca%acity + the !tr*ct*ral member, D i! the deadClad eect n the member,8 i! the liveClad eect n the member, - i! the im%act +actr, 41 i! the +actr+r dead lad!, and 4 i! the +actr +r live lad!. he deadClad +actr 041e*al! 1.3 +r all rating level!, and the liveClad +actr 04 e*al! .17 +rinventry level and 1.3 +r %erating level.

=a%acity 0= i! calc*lated a! *tlined in the 44S&O&tandard &peci)cationsfor !igh"ay #ridges

. he !tr*ct*ral lay*t and material! determine theca%acity. r lad rating, ca%acity de%end! n the %re!ent cnditin + the!tr*ct*ral cm%nent!. here+re, engineer! need t acc*nt +rb!ervatin! !*ch a! crac'ed r deterirated !ectin! when %er+rmingca%acity calc*latin!.

-n lad +actr rating calc*latin!, dead lad! 0D are %ermanent lad! that dnt change a! a +*nctin + time. $enerally, +r bridge!, dead lad! incl*de


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!el+ weight and any %ermanent eternal lad!. 8ive lad! are tem%rarylad! that act n a !tr*ct*re. 4! de;ned in the 44S&O &tandard&peci)cations for !igh"ay #ridges, the de!ign live lad i! de;ned a!&2?&S2 tr*c' lading r lane lading *!ing the lad that %rd*ce! thelarge!t mment r !hear. 44S&O e!tabli!hed the &2 and &S2 tr*c'! a!

!tandard liveClad mdel! t +acilitate a !im%ler analy!i! ba!ed n ana%%rimatin + the act*al live lad@ they are nt meant t re%re!ent act*alvehicle!. Similarly, !tandard lane lading %rvide! a !im%le methd +rcalc*lating a bridgeE! re!%n!e t a !erie! + tr*c'!. Bridge wner! al! cancalc*late the di!trib*tin + live lad t a !ingle !tr*ct*ral member a!*tlined in the 44S&O !%eci;catin!.

he lad +actr rating de!ign lad! d nt ade*ately re%re!ent c*rrent lad!n the highway! and d nt %rvide a *ni+rm !a+ety level +r vari*! bridgety%e! and !%an length!. here+re, legal lad calc*latin! are cmmnly*!ed t en!*re the !tr*ct*ral integrity + %*blic bridge!. hree 44S&O legal

lad! %rd*ce cntrlling mment and !hear reactin! +r the !hrt,medi*m, and lng !%an! re!%ectively. -n additin t 44S&O legal lad!,many State DO! have StateC!%eci;c legal lad! that are *!ed in lad ratingcalc*latin!.

Bridge wner! al! can chec' %ermit lad! *!ing lad +actr rating whenthey receive re*e!t! +r verlad %ermit!. -n %ermit lad rating, the weightand dimen!in! + the act*al tr*c' !h*ld be *!ed in %lace + the 44S&Olad mdel!.

he lad +actr rating im%act +actr 0- i! added t all live lad! t acc*nt +r

the !%eed, vibratin, and mment*m + vehic*lar trac. he 44S&O!%eci;catin! +r bridge de!ign de;ne the im%act +actr a! +llw!A

4+ter determining the rating +actr +r a !tr*ct*ral member, the bridge wnerthen m*lti%lie! the rating +actr by the weight + the live lad tr*c' t yieldthe bridge member rating +r that member. he verall rating + the bridge i!cntrlled by the !tr*ct*ral member with the lwe!t rating.


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These illustrations show ''S$Tlegal loads, which control weightlimits for short- (Type ) *nit+,medium- (Type )-S *nit+, and long-

(Type )-) *nit+ span bridges,respecti!ely. The T refers to weightin tons, and / refers to weight inkips (0,111 pounds or 213 metrictons+.

"oad and #esistance &actor #ating

4! with lad +actr rating, bridge wner! can calc*late lad rating! n bth%erating and inventry level! *!ing the 8 methd. -n additin, 8

*!e! limit !tate! +r !trength, !ervice, and +atig*e t en!*re !a+ety and!erviceability in the lad rating. he!e limit !tate! were intrd*ced in the44S&O 8D !%eci;catin!. he strengthlimit !tate acc*nt! +r the!trength ca%acity + the !tr*ct*re *nder %ermanent and live lading. he!ervice limit !tate acc*nt! +r !tre!!, de+rmatin, and crac' width.he fatigue limit !tate acc*nt! +r cyclical !tre!! range! t avid +atig*ecrac'ing. Strength i! the %rinci%al limit !tate and, there+re, i! the main


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determinant +r bridge %!ting, cl!ing, and re%air. Bth !ervice and +atig*elimit !tate! can be a%%lied !electively t bridge!.

4! !tated in the 44S&O Manual for Condition Evaluation of #ridges, theba!ic 8 e*atin! are a! +llw!A

-n the e*atin!, i! the rating +actr, = i! the !tr*ct*ral ca%acity, n i! thenminal member re!i!tance 0a! in!%ected, D= i! the deadClad eect +!tr*ct*ral cm%nent! and attachment!, D" i! the deadClad eect +wearing !*r+ace! and *tilitie!, P i! the %ermanent lading ther than dead

lad!, 88 i! the liveClad eect, - i! the dynamic lad allwance, D= i! the8D lad +actr +r !tr*ct*ral cm%nent! and attachment!, D" i! the8D lad +actr +r wearing !*r+ace! and *tilitie!, P i! the 8D lad +actr+r %ermanent lad! ther than dead lad!, 8 i! the eval*atin liveClad+actr, c i! the cnditin +actr, ! i! the !y!tem +actr, and + i! the 8Dre!i!tance +actr.

/minal re!i!tance 0n i! the ability + the bridge t with!tand a%%liedlad!. e!i!tance m*!t be calc*lated t determine the ca%acity + the bridge.r lad rating, re!i!tance de%end! n the !tr*ct*ral lay*t, bridge material,and thepresent condition+ the !tr*ct*ral cm%nent!. 4+ter determining

the nminal re!i!tance, a bridge wner can calc*late the ca%acity bya%%lying the %rd*ct + the three !a+ety +actr!A , c, and !. here!i!tance +actr 0 i! the !ame +actr *!ed in 8D bridge de!ign andacc*nt! +r the general *ncertaintie! + a bridge member in !ati!+actrycnditin. he cnditin +actr 0 c i! *!ed t acc*nt +r increa!ing*ncertaintie! in a bridge member nce it! cnditin deterirate!. hecnditin +actr i! e*al t 2.F5 +r member! in %r cnditin, 2.95 +rmember! in +air cnditin, and 1.2 +r member! in gd cnditin. he!y!tem +actr 0 ! acc*nt! +r the level + red*ndancy in the !tr*ct*re.Bridge! that are le!! red*ndant r nnred*ndant will be a!!igned a lwer!y!tem +actr and there+re will have red*ced calc*lated ca%acitie!.


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-n 8 calc*latin!, %ermanent lad! are !e%arated int the three variable!D=, D", and P, beca*!e each i! a!!igned an inde%endent lad +actr 0 +reach lad rating limit !tate. 4ll %ermanent lad! are calc*lated in accrdancewith the bridge cnditin! at the time + the analy!i!. 8ad +actr! +r%ermanent lad! and live lad! are !%eci;ed in the 44S&O Guide Manualfor Condition Evaluation and Load and Resistance Factor Rating (LRFR of!igh"ay #ridges.

4! with lad +actr rating, 8 live lad! are tem%rary lad! that act n a

!tr*ct*re. #ehic*lar lad! are the %rimary live lad! that aect bridge!. rnn%ermit lad rating, the 8 !y!tem i! a tiered a%%rach. he bridgewner %er+rm! an initial chec' ba!ed n the &8C93 de!ign lad at thea%%licable de!ign limit !tate!. 4! with &2?&S2 lading, 44S&Oe!tabli!hed &8C93 a! a !tandard mdel +r live lad!, ! it de! nt re%re!entan act*al vehicle. The $"-2) load model under the "#&4 methodologyis e5ui!alent to the $16$S1 model truck in combination with the$S1 uniform lane loading.he lad rating e*atin ha! been calibrated


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!*ch that i+ a chec' + the de!ign lad yield! a !ati!+actry lad rating, thenthe bridge wner can a!!*me that the bridge will yield !ati!+actry ladrating! +r all 44S&O legal lad!. here+re, an inventry de!ign lad ratingre!*lting I1 re*ire! n +*rther legal lad analy!i!.

Bridge wner! generally %er+rm legal lad rating nly a! a !ecndCleveleval*atin when &8C93 lad! eceed the bridge ca%acity. 8egal lad rating%rvide! the lad ca%acity + any + the 44S&O r State mdel! +r legallad. 0/teA -+ State! devel% their wn legal lad!, wner! need t %er+rman analy!i! t en!*re that the StateC!%eci;c lad! are envel%ed within the&8C93 de!ign lad.

7nspectors deemed this bridge closurenecessary based on a load ratingcalculation.

inally, wner! %er+rm %ermit lad rating nly +r vehicle! carrying lad!that eceed the legal limit. Permit %rced*re! a%%ly nly t bridge! that haveade*ate ca%acity t carry de!ign r legal lad!. -n %ermit lad rating, the

weight and dimen!in! + the act*al tr*c' !h*ld be *!ed in %lace + the44S&O lad mdel!.

8alibrating "#

"hen calibrating any de!ign r eval*atin cde, engineer! devel% a%rced*re t acc*nt +r !tr*ct*ral reliability r, cnver!ely, the %rbability+ +ail*re. he 8, li'e the 8D cde, ba!e! thi! reliability n the !a+ety


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inde 0 !y!tem, where, a! de!cribed in the /atinal =%erative &ighwaye!earch PrgramE! C!R/ Report o. 0102 Calibration of Load Factors forLRFR #ridge Evaluation, i! de;ned a! +llw!A

Sa+ety -nde, J mean val*e + g

Standard deviatin + g

g J e!i!tance C Dead 8ad C 8ive 8ad K -m%act

4! the e*atin! indicate, large %!itive val*e! +r g 0a %!itive val*eindicate! a !a+e element and?r !mall val*e! +r the variatin + g will yielda higher !a+ety inde. &igher !a+ety indice! mean higher reliability. Sa+etyindice! %rvide a mea!*re + the !tr*ct*ral reliability r, cnver!ely, the ri!'that a de!ign cm%nent ha! inade*ate ca%acity in a given limit !tate.

Selecting a target b i! ba!ed n ecnmic!. -ncrea!ing the !a+ety inde can

lead t c!tly vercnC!ervative de!ign and eval*atin, while decrea!ing the!a+ety inde can lead t e%en!ive maintenance r re%lacement + +ailedcm%nent!. r 8D, the target !a+ety inde ch!en wa! b e*al! 3.5.4!!*ming a nrmal di!trib*tin, thi! !a+ety inde en!*re! that d*ring thede!ign li+e + the !tr*ct*re, nly *t + 12,222 cm%nent! will e%eriencelading that eceed! the cm%nentE! re!i!tance, a! &"4E! yint 8winnted in the article G"hy the 44S&O 8ad and e!i!tance actr De!ignS%eci;catin!LH %*bli!hed in 1999 in Transportation Research Record 34566.

he 8 target !a+ety inde i! b e*al! .5 at %erating level and e*al!3.5 +r inventry level. he %erating !a+ety inde + e*al! .5 en!*re!

that nly 6 *t + 1,222 cm%nent! will e%erience lading that eceed! thecm%nentE! re!i!tance. he %erating reliability can be )*!ti;ed n manygr*nd!, incl*ding the +act that the e%!*re %erid +r eval*atin i! m*ch!hrter 0 t 5 year! between in!%ectin! cm%ared t the 75Cyeare%!*re %erid +r de!ign. -n additin, the relative c!t +r increa!ing the!a+ety inde d*ring the eval*atin %ha!e i! m*ch higher when cm%ared tthe c!t + increa!ing the inde d*ring the de!ign %ha!e.

he lad and re!i!tance +actr! , c, !, D=, D", and 8 are calibrated*!ing the !elected !a+ety inde target! t achieve *ni+rm !a+ety +r allmaterial ty%e!, !%an!, and lad eect!.

Beca*!e the 8 liveClad +actr! de%end n average daily tr*c' trac04D, re!earcher! *!ed trac data +r calibratin. hey *!ed weighCinCmtin data +rm !ite! with 4D val*e! + at lea!t 5,222 t determine the%rbability + !ideCbyC!ide heavy vehicle event!. he re!earcher! *!ed the;eld data in a tracC:w mdel t inter%late %rbability val*e! +r ther4D val*e!.


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*nderstanding the 'd!antages

enable a !mth tran!itin +rm lad +actr rating, the 8 re!earchteam !et a gal t ma'e the man*al %ractical and ea!y t *!e. G4lth*gh!me bridge wner! may thin' that it will be mre dic*lt t *!e, 8 i!

act*ally a! ea!y, i+ nt ea!ier, t *!e than 8,H !ay! ira! -brahim, !enirbridge cde! and !%eci;catin! engineer at &"4.

he lad and re!i!tance +actr! are calibrated t acc*nt +r the !a+etyreliability, ! thi! a!%ect remain! invi!ible t the eval*atr. -n additin,lading %rced*re! were de!igned t a%%ear t be an eten!in + thec*rrent lad +actr rating methd.

4! with 8D, 8 %rmi!e! a mre *ni+rm level + !a+ety and a lwer ri!'+ verC r *nderde!igned member!. he 8 a%%rach can lead t adecrea!e in c!tly trac re!trictin! and bridge !trengthening r re%air! a!

well.

4lth*gh the general e*atin! are !imilar +r the c*rrent 8 and new 8methdlgie!, and the %rced*re! are !traight+rward, the im%lementatin+ a new lad rating methd can be timeCcn!*ming and c!tly +r StateDO!. /everthele!!, the +llwing i! a li!t + credible rea!n! t )*!ti+yad%ting the new 8 %rced*re!.

1. 8 %rvide! a !im%li;ed a%%rach thr*gh the *!e + the &8C93 livelading a! a !creening chec' +r all ther legal lading. Previ*!ly, with8, the &S2 tr*c' did nt re%re!ent c*rrent highway cnditin! and

did nt %rvide *ni+rm reliability ver varying !%an length!. achievereliability, State! a%%lied lad +actr rating t three !e%arate 44S&Olegal lad mdel!, with each ne cntrlling !hrt, medi*m, r lng!%an! re!%ectively. Only the cmbined *!e + the three 44S&O legallad! re!*lted in *ni+rm reliability. "ith 8, the &8C93 can achievethi! *ni+rm reliability +r all !%an length! with nly ne ladcmbinatin.

. 8 enable! bridge wner! t a%%ly trac vl*me and ther !iteC!%eci;c data when determining liveClad +actr! +r a bridge. -+ mrein+rmatin i! available, !*ch a! tr*c' lad! thr*gh weigh !tatin!,

eval*atr! may ta'e a mre re;ned a%%rach by e!timating !iteC!%eci;c lad +actr! that are characteri!tic t the bridge !ite. hi!%rced*re c*ld be e!%ecially advantage*! t bridge! carrying lighttr*c' trac.

3. 8 +acilitate! *!ing the %a!t %er+rmance + a bridge t hel%determine it! !erviceability rating. -+ in!%ectr! ;nd n %rblem! with%a!t %er+rmance, re!trictive lad %!ting ba!ed n calc*lated


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!erviceability %er+rmance mea!*re! may nt be )*!ti;able. -n ca!e!li'e thi!, eval*atr! can *!e %a!t %er+rmance a! a %r+ te!t +r!erviceability.

(. 8 %rvide! %rced*re! +r lad rating vehicle! with lad! that

eceed the legal limit 0r %ermit vehicle!. he!e %rced*re! incl*deliveClad +actr! !%eci;c t %ermit lading.

5. 8 %rvide! %rced*re! +r eval*ating +atig*e n ei!ting !teelbridge!, cmbining !%eci;catin! +rm 44S&OE! g*ide &peci)cationsfor Fatigue Evaluation of E*isting &teel #ridges and ''&!T7%s LRF8#ridge 8esign &peci)cations.

6. 8 de!cribe! %rced*re! +r nnde!tr*ctive lad te!ting, whichinvlve! ;eld b!ervatin! and mea!*rement! + in!ervice bridge!.Beca*!e bridge rating! tend t be +airly cn!ervative, ;eld lad te!ting

+ten can reveal additinal ca%acity, a! nted by ichael Bar'er inGM*anti+ying ieldCe!t Behavir +r ating Steel $irder Bridge!,H%*bli!hed in the N*ly?4*g*!t 221 i!!*e + the9ournal of #ridgeEngineering.

7. 8a!tly, the /=&P Pr)ect =1C(6 re%rted that in trial lad rating!GDO rating engineer! were able t %er+rm the 8 eval*atin!with*t *nd*e dic*lty and with relatively +ew errr!.H hi! ;ndingdemn!trate! that bridge eval*atr! d *nder!tand the %rced*re!and that im%lementatin i! +ea!ible.

GBridge wner! need a rating methdlgy that %rd*ce! re!*lt! that arecl!er t reality, nt cl!er t %rir rating methdlgie!,H !ay! -brahim. Ghe8 methdlgy %rvide! a reality chec' and %rd*ce! meaning+*l,reliable re!*lt! that are !*%erir t th!e + %rir rating methdlgie!.H

&ield Trials and 8omparisons

"hile devel%ing the new 8 man*al, /=&P re!earcher! cm%ared 8and lad +actr rating! n !everal act*al bridge! re%re!enting vari*! ty%e!and %hy!ical cnditin!. >val*atr! %er+rmed rating! at bth inventry and%erating level! *nder de!ign and legal lad! and %re!ented their re!*lt! +r

three gr*%! + bridge!A !teel m*ltigirder, rein+rced cncrete Cbeam, and%re!tre!!ed cncrete -Cbeam bridge!.

r !teel m*ltigirder bridge!, 8 de!ign inventry rating! were !lightlylwer than lad +actr rating bridge!. 8wer rating! indicate a mrecn!ervative re!*lt and lwer allwable lading. 8 de!ign %eratingrating! were lwer than lad +actr rating. he 8 legal lad rating! werehigher than inventry rating! and alm!t e*ivalent +r %erating rating!


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*!ing the lad +actr rating methd. he re!earcher! al! %er+rmed trialrating! n nnred*ndant !teel bridge! b*t determined that the n*mber +bridge! !t*died wa! t !mall t %ermit drawing any cncl*!in!.

r rein+rced cncrete Cbeam bridge!, 8 de!ign lad rating! were lwer

than th!e achieved *!ing lad +actr rating +r bth inventry and %eratinglevel!. 8egal lad rating! +r 8 were higher than th!e +r lad +actrrating +r inventry b*t lwer +r %erating.

he re!*lt! +r %re!tre!!ed cncrete were mre widely !cattered than th!e+r !teel r rein+rced cncrete. he ma)rity + lad rating! achieved *!ingthe 8 a%%rach +r the %re!tre!!ed cncrete bridge! were gverned by!hear rather than :e*re !tre!!e!, which i! a !*b!tantial dierence +rm thelad +actr rating methd where :e*ral rating! ty%ically gvern +r allbridge ty%e!. he re!earcher! attrib*te the rever!al d*e t a n*mber +i!!*e!. r the de!ign limit !tate, the 8 &8C93 lading ca*!e! higher

!hear !tre!! than the &S2 lading. -n additin, the !hear di!trib*tin +actr!are higher *!ing the 8 methd. !t im%rtantly, the eval*atr! *!ed themdi;ed cm%re!!in ;eld thery t calc*late !hear re!i!tance in!tead +the %revi*! !emiem%irical +rm*la.

r %re!tre!!ed cncrete, the re!*lt! generated thr*gh the mdi;edcm%re!!in ;eld thery can be very dierent than th!e +r lad +actrrating. &wever, in accrdance with the 44S&O Guide Manual for ConditionEvaluation and Load and Resistance Factor Rating (LRFR of !igh"ay#ridges, in!ervice cncrete bridge! that !hw n !ign! + !hear di!tre!! dnt need t be chec'ed +r !hear when rating +r de!ign r legal lad.

0>val*atr! !till need t chec' !hear +r the %ermit lad rating.

9o!ing Toward 7mplementation

date, !everal State! have either +*lly r %artially ad%ted 8D a! their%rimary de!ign methd +r bridge!. ew State!, hwever, have ad%ted 8a! their %rimary methd +r lad rating. 4 recent !*rvey + 3 State! !hwedthat 15 have *!ed 8 in nly !am%le lad rating. Beca*!e themethdlgy + 8 i! !ynnym*! with 8D, advancing the

im%lementatin + the latter will hel% with the event*al ad%tin + the+rmer. 4dditinal !am%le rating!, training, and re!earch can hel% the bridgeengineering cmm*nity gain the cn;dence it need! t +*lly im%lement thenew 8 methd acr!! the United State!. G4lth*gh State! and therbridge wner! may be ca*ti*! ab*t embracing thi! new a%%rach,H !ay!>d "a!!erman, directr + the !tr*ct*re! divi!in at enne!!ee De%artment+ ran!%rtatin 0DO, Gwe *nder!tand that 8 er! an a%%arent


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im%rvement in reliability and *ni+rmity when rating bridge!. "e e%ectthat any i!!*e! will be vercme with time.H

The map shows the status of "#&4implementation across the *nitedStates as of 'pril 11: (the latest datefor which information was a!ailable atthe time of publication+.S*rceA &"4.

he recently relea!ed 8 !+tware that wr'! with the %%*lar cm%*terCba!ed tl Bridge ating and 4naly!i! + Str*ct*ral Sy!tem! r B4SS!h*ld hel% ea!e the cncern amng State! ab*t the time and ert thatwill be inve!ted in !witching t 8. 4! State DO! mve thr*gh the%rce!! + im%lementing 8D and 8, &"4 !ta member! are available+r technical a!!i!tance and cn!*ltatin.

#eferences

1. 4merican 4!!ciatin + State &ighway and ran!%rtatinOcial!.''&!T7 LRF8 #ridge 8esign &peci)cations. 3rd >d."a!hingtn, D=A 44S&O, 22(.


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. 4merican 4!!ciatin + State &ighway and ran!%rtatinOcial!. Guide &peci)cations for &trength Evaluation of E*isting &teeland Concrete #ridges. "a!hingtn, D=A 44S&O, 19F9.

3. 4merican 4!!ciatin + State &ighway and ran!%rtatin

Ocial!. Manual for Condition Evaluation of #ridges. nd >d."a!hingtn, D=A 44S&O, 222.

(. 4merican 4!!ciatin + State &ighway and ran!%rtatinOcial!. Guide Manual for Condition Evaluation and Load andResistance Factor Rating (LRFR of !igh"ay #ridges. "a!hingtn, D=A44S&O, 223.

5. 4rmbrecht, im. -llini! De%artment + ran!%rtatin. G8 S*rvey +r#OBU$ State!.H Pre!entatin t #irti!?O%i!?B4SS U!er! $r*%, N*ly22(.

6. Bar'er, ichael. GM*anti+ying ieldCe!t Behavir +r ating Steel $irderBridge!.H9ournal of #ridge Engineering. N*ly?4*g*!t 221A 5(C61.

7. GBridge 8ad ating and 8D Bridge De!ign S+twareH "eb !ite +r44S&O Bridge"are >ngineering anagement S+tware. arch223. htt%A??aa!ht.ba'er%r)ect!.cm?virti!?#irti!O%i!Brch*re2323.%d+.

F. Den!mre, David. G8ad and e!i!tance actr De!ign 08D em.H&"4 %licy memrand*m. N*ne

222.www.+hwa.dt.gv?bridge?26F22.htm.

9. $drich, B.8. and P*c'ett, N.4. G=m%ari!n + 8 and 8 +r=ncrete Bridge!,H Prceeding! +rm the 22 =ncrete Bridge=n+erence, !%n!red by &"4 and the /atinal =ncrete Bridge=*ncil, /a!hville, /, Octber 6C9, 22.

12. $rdn, Stanley. GBridge 8ad ating! +r the /atinal Bridge-nventry.H &"4 %licy memrand*mA Oce + >ngineering./vember1993. www.+hwa.dt.gv?leg!reg!?directive!?%licy?nv5.htm.

11. &artle, aymnd, hma! yan, N. >ric ann, 8e!lie Danvich,"illiam S!', and N*!tin B*!cher. #ridge $nspector%s ReferenceManual. #l. 1. P*blicatin /. &"4C/&-C23C221, 22.

1. 8ichten!tein =n!*lting >ngineer!, -nc. G/=&P "eb Dc*mentF 0Pr)ect =1C(6A =ntractrE! inal e%rtA Gan*al +r =nditin>val*atin and 8ad ating + &ighway Bridge! U!ing 8ad and
http://wwwcf.fhwa.dot.gov/exit.cfm?link=http://aashto.bakerprojects.com/virtis/VirtisOpisBrochure0303.pdfhttp://wwwcf.fhwa.dot.gov/exit.cfm?link=http://aashto.bakerprojects.com/virtis/VirtisOpisBrochure0303.pdfhttp://www.fhwa.dot.gov/bridge/062800.htmhttp://www.fhwa.dot.gov/legsregs/directives/policy/nov5.htmhttp://www.fhwa.dot.gov/bridge/062800.htmhttp://www.fhwa.dot.gov/legsregs/directives/policy/nov5.htmhttp://wwwcf.fhwa.dot.gov/exit.cfm?link=http://aashto.bakerprojects.com/virtis/VirtisOpisBrochure0303.pdfhttp://wwwcf.fhwa.dot.gov/exit.cfm?link=http://aashto.bakerprojects.com/virtis/VirtisOpisBrochure0303.pdf


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e!i!tance actr Phil!%hy.H ay221. htt%A??g*lliver.trb.rg?%*blicatin!?nchr%?nchr%wF.%d+.

13. 8win, yint. G"hy the 44S&O 8ad and e!i!tance actrDe!ign S%eci;catin!LH Transportation Research Record 34566. 1999A

173C176.

1(. inervin, =harle!, Bala Siva'*mar, red !e!, Denni! ert

AASHTO Load Ratings-3 & Looking to LRFR

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