BRIDGE FATIGUE GUIDE - AISC
BRIDGE FATIGUE GUIDEDESIGN AND DETAILSAMERICAN INSTITUTE OF STEEL CONSTRUCTION
BRIDGE FATIGUE GUIDEDESIGN AND DETAilSbyDr. John W. FisherProfessor of Civil EngineeringFritz Engineering LaboratoryLehigh UniversityBethlehem, PennsylvaniaAMERICAN INSTITUTE OF STEEL CONSTRUCTION400 North Michigan Avenue, Olicago, IL 60611
AISC Committee on BridgesA. C. Van Tassd, ChamnanPlitsburgh-Des MOines Steel Co.Lawrenet . BIgelowAmencan Bridge DWlSlon,Steel CorporatIOn.Donald C. Frederickson (AdvISory)Bethlehem Steel Corp.Wesley A. KingK 6- S Englneenng Co.J ohn F. W. KochInternatIOnal Steel ComponyAndrew LallyAmencan In slltute oj Steel ConstructIonWilliam A. MilekAmencan In slltute oj Steel ConstructIOnWerner QuasebarthAlias Machllle 6- Iron Works, In c.Brock C. RowleyBmtol Steel 6- Iron Works, In c.John L. SallyPeden Steel CompanyRobert S. ShermanCarolina Steel CorporatIOnRaymond H . R. TideAmencan Inslltute oj Steel ConstrucllonF. Ayers WilliamsonAmencan In slltute oj Steel ConstructIOnu.s.AREA AdvisorsJohn E. BarrettAlfred Benesch 6- Compony, Consulting EngineersJohn W. HartmannBurlington Northern, In c.AASHTO AdvisorsCharles PcslOtnikIowa Department oj TransportatIOnFrank D . SearsFederal I h ghway AdmlntstrallonCarl E. Thunman, Jr.illinois Department oj TransportatIOnAssociate AdvisorHugh KrentzCanadzan InstItute of Steel Construct ronCopyright 1977 by Amencan Inslltute oj Steel Construction, In c.All nghts reserved. No port oj thIS publICation may be reproduced WIthout WrItten penntSSlon.The material presented in this publication has been prepared in acoordanet with recognizedengineering principles and practices and is for general information only. The reader iscautioned that independent professional judgment must be exercised at all times when thedata or recommendations SCI forth in this publication are considered and / or applied. Thepublication of the material contained herein is not intended as a rtpresenlation or warrantyon the part of the American Institute of Steel Construction-or of any other person namedherein-that this infonnation is suitable for any general or particular use, or of freedom frominfringement of any patent or patents. Anyone making USe of this information assumes allliability arising from such use. The material contained herein is not set forth for purposesof design, but as a guide only. The design of structures is with," the scope of expertise of acompetent licensed architect, structural engineer, or other licensed professional for the ap plication of principles to a particular structure.
PREFACEIt is estimated that the.- a.- mo.- than one-half million steel highway and railroad brid esin the United States. With only a few exctptions, these structures have performed ","isf.tnonlyin e. . ery respect and, in mosl cases, have c.:1rrird loads far in excess of those for which theywere designed .During the past decade, a great deal of research has been focused on the effects of the repetitive loadings to which highway and railroad bridges are subjected This work, a wellas lessons learned from the reiatively few cases of undesirable performance, have led to abettor understanding of bridge fatigue behavior and to substantial changes in fatigue pro-Ylsion of bridge design specifications.This booklet has been prepared as a gu.de to the general problem of bridge falJ ue andto a is! the designer with the selection and design of bridge details that offer superior falJ uestrength. It is a revised and expanded ver ion of theearlier AI C booklet GUIde to th.' 1'174AA liTO Fallgue SpecificatIOns.ince 1974 , ponions of the AA HTO fatigue specifications have been adopted by AREAand AI C. Hence the classification of various details and their permissible stressran eforspec.fied load cycles is now identical for all three specifications. As a resuit, the general application of the AA HTO fatigue provisions to the design examples for highway bndgesare equally applicable to other structu.-s. Olmously, the loading conditions and desi n lifecritoria will differ, depending on the application.A method for estimating equivalent design life for use with constant cycle fatigue stressesis described for highway bridges. This permits the potential cumulative damage of randomtruck traffic to be accounted for in design A romparable approa h for railroad brld e canalso be found in the Commentary to the AREA Specification, reproductd in AppendIX BOne of the majOr fatigue problems that has surfaced in .-cent years i crackin from e('ondary and displactment-inductd stresses. D.scussed brieny in the 1974 Guide, thIS ubJC 1IS treated In much greater depth in Chapter 5 of thIS booklet. The problem has de.e1opedbecause many bridges are essentially linear structures and are designed for in-plane loadingand deneaion of the main girders and the cross·framing. However, even though intr-raC'tlonbf:tween the longitudinal and transve framing does not alter the in-plane behavior of th framing enough to economically justify a spact frame analysis, it is of p.1ramount .mpon.nctto cons.dor the distonions resulting from such intoraction. Genoraliy, tht effects of secondaryand displacement-induced stresses are seen at conneCtions to main members. The . . r-rit)·is often dependent on geometrical conditions which the designer can control. These are discussrd at length and recommendations provided as to how the problem may be minimizedor avoidtd. A general procedure for the design of connections to insure the intendtd performanct is provided at the end of Chapter 5.The direct applicability of fatigue specifications to the main load carrying member hasusuall} been "C)' appartnt to bridge drsi nors. As a result, appropriatO details ha\e enprO\:idr ! which satisfy the specification requirements. Howe . . er. the design of SttOndarymembers and conntttions has not always bttn as obvious. Often thest members interi.Kt withthe mam members and receive more numerous cycles of stress with a higher stress rang th lnassumr !. Discussion of this problem is provided and recommendations given on the treatmentof such components.A brief discussion of the background and history of fatigut spe ifications for h. h\Vaybridge. is provided, as wtll as a summary of tht laboratory studies on fatigue that form therationale for the stress range concept and leadlOthe current specification provisions.Aniele 1.7.2 of the 1977 AASHTO Specifications, and Art. 1.3.13 of the 1977 AREApecifications and its Commentary, arereprodll d111in full in Appendix B They contain the
major changes to Art. 1.7.3 of the 1973 AASIITO p cifications and Art. 1.3. 13 of the 1976AREA p eifications. These changes ar summarized at the beginning of App :ndix B.The causes of fatigue problems and a number of examples are examined in detail in thISbooklet. The recommendations provided throughout are intended to aid in minimizing andavoiding these problems in the future. The ustr is urged to examine in detail the varioussections of this booklet throughout the design of a cyclically loaded Structure.This book let was sponsored by the American Institute of Steel onstruction under theauspices of the AISC Commillee on Bndges. The author is indebted to the Commillee andliS Advisors for their many suggestions and adviee. The AISC Commillee also provided thedesign exam ples contained herein.Acknowledgment is also due those organizations who sponsored research at Fritz Engi.neering Laboratory, Lehigh University, into the fatigue behavior of welded steel details.Much of the research provided background and eXp :rientt for the preparation of this booklet.Those sponsoring research work include the Pennsylvania Department of Transportation ,alional Cooperative Il ighway Restarrh Program- Transportation Research Board,National Academy of Sciences, and the Un lied States Department of TransportationFederal Highw ay Administration.The author would like to acknowledge his colleagues and Research Assistants who haveworked with him on various research projects: P A. Albrecht, K. D . Boyer, A. Coates, JII. Daniels, D. A Erb, K. II. Frank , W. C. Ilerbein, M . A. Hirt, G . J. Inukai, G . R. Irw in ,R. Jaccard, D . J. Klingerman, N . V. Marchica, B M . )'IcNamee, A. W Pense, R. Robert.,R. E. lock bower, f I. Woodward, B. T Yen, and N . Zwlemoyer. Also, H T . utherland,Instruments ASSOCIate, and the laboratory support staff under the sup :rvision of K. Il arp :l,R. R. Dales, K. Eberts, a nd R. Hillinger, provided invaluable assista nee throughout thelaboratory and lield in vestigations.Thanks are also due Ruth G rimes for her assistanee with the preparation of the manuscriptand to R. Sopko for the photographic coverage.May, 1977J ohn W . FisherI.
CONTENTSPreface . . . . . . . , . . . . , . . . . . . . . IIIFati ueChaptc:r 1.Design Details to OptimizeStrength . . . . . . . . . . . . . . Chapter 2.Design Examples . . . . . . . . . . 7Chapter 3.Stress Cycles for Design . . . . . . . . . . . . . . 1.Chapter tStress Range Concept . . . . . . . . . . . . 17Inni al Discontinuilles 17Fatigue Strength 17Residual Stressts 19Variable Stress Cycles 19Curr!.": nl Research '20Chapter 5.Connections-Fatigue Considerations as a Result of Secondary Slrcs! c! . . . . 21Restraint al Simple: End Connections 21Problems with Dislorllon of Simple End Conntcl lOn ComponentsProblems with RestraintSummary a nd Recommendations for Simple Connections Subjertcd10 CyclicaJ LoadsDisplace ment s at Stringer Connections a nd Web Brarkets!25Flange Twisting and lor Lateral M ovementRecommendations to Minimi tt the Effects of Out·of·Plane Movementat Stringer Con nect ionsOut·of·Plane Displacements at Floor Beam Connect ion Pl atts andTrans\lerse St iffeners ,' 28End Rota tion of Floor Bea msTrans . erse SlifftntrsSummary and Recommendations for Floor Beam Con ntctlon Platesand Tra nsverse StiffenersSuggested General Procedure for Design of Connections,' 3 !Chapter 6.Secondary MembeTS and Connections . . . . . . . . 32Dis placements at Diaphragms and Cross· Frames '32Summary and Recommend ations for Diaphragms and Cross· Frames 3"Lateral Bracing and Lateral Gusset Plates/ 34Out-of-Plane M ove ment at Late ra l Gusset Pl atesStresses in Lateral Gusset PlatesVibration of Late ral BraCingRecommended Details at Lateral Gusset Plates/ 37Chapter 7.Miscellaneous Fatigue Considerations . . . . . . . . . . 39Displacement Induced Secondary Stresses in Other Structural Systems 39Out-or-Plane Bending in Connection Pl ates of Cantilever Floor Beam Brack('tsRecommended Details for Cantilever Bracket Connection Pl atesSecondary Bending Stresses in Truss J ointskewed Bridges/ 41Onhotropic Sted Decks/ 42Weld Requirements and Special Considerat ions 43Groove Welded Spli Transition RadiiAppendix A.References . . . . . . . . . . . . . . 4SAppendix B.AASHTO and AREA Fatigue Specifications . . . 47AASHTO Article 1.7.2/ 47AREA Articles 1.3.13, 2.3.1 and Commentary Articles 9.1.3.13 and 9.2.11 ' 52v
Design Details1CHAPTER 1DESIGN DETAILS TO OPTIMIZE FATIGUE STRENGTHThe major factors governing fatigue strength are the appliedstress range, the number of cycles, and the type of detail.(ruttural details behave differently because the stress con· nlration condition changes. The inherent variability of initialdiscontinuities is also a major factor.All welding processes introduce small discontinuities in ornear the weldment. Although good welding practice willminimize the number and size of these discontinuities, theycannot be eliminated. The fatigue design rules were developedfrom research on test specimens that contained normaldisronlinuities. The usual visual inspection of fillet welds andlongitudinal groove welds and the nondestructive inspectionof transverse groove welds in tension nanges may detectdiscontinuities that are adequately accounted for in the designprovisions for fatigue. In fact most attempts to remove al·lowable discontinuities from manufacturing and fabricationthat are permitted by ASTM and A WS will result in a condition that is worse than the original condition.For design there are two options available: (I) the choi eof a detail (or the severity of the stress concentration introducedby a detail) and (2) limiting the stress range to acceptablelevels.Details that provide the lowest allowable stress range in·vo}o.;e connections that experience fatigue crack growth fromweld toes and weld ends where there is a high stress concentration . This is true of both fillet and groove welded details.Dctails which serve the intended function and provide thehighest fatigue strength should be considered.As a general rule, details which involve failure: from internaldiscontinuities. such as porosity, slag inclusion, cold laps, andother com!,,1rable conditions, will have a high allowable stressran e. This is primarily due to the fact that there is no geometrical stress concentration at such discontinuities other thanthe effect of the discontinuity itself.The AA HTO Specifications, in Table 1.7.2A2 (see Appendix B), describe \'arious situations and categories. imilarprOVISions are provided by AREA in Table 1.3.13C (see.\ ppendix B). A more detailed evaluation of typical weldedbridge details for fati ue loading is given in Ref. I.The stress cycles for faligue design stresses are defined bythe bridge location and type of member (see Table 1.7.2B).The maximum stress ranges permitted on the bridge for thevarious stress cycles are listed in Table 1.7.2A l of theAAS HTO Specifications. Tables 1.3.13A and B provide thisinformation in the AREA pecifications. If well defined trafficconditions are known, lhese should Ix used in lieu of the Slresscycles in Table 1.7.2B or in Table 1.3.13B to determine asuitable design life and the corresponding allowable stressranges; the use of an equivalent design life tS discussed inChapter 1Thus, the designer can, to a large extent, control the typeof detail selerted and its location in regions of significant cyclicstress. Every attempt should be made to place Category Edetails in regions of low cyclic stress, so that the member sizeneed not be increased. For example, coverplated beams canhave the cover plate termination extended into regions of lowstress range.A wide class of fi llet and groove welded details is coveredby Category E.' Ilowever, alternate details which result inhigher allowable stress ranges are available and can beused.For example, transverse or lateral bracing which framesinto a girder, as illustrated in Figs. I and 2, results in a Cat·egory E detail on the nange surface at the weld end . If thestress range is critical, details such as shown in Figs 3 and 4will provide much higher allowable stress ranges. Also, asshown in Fig. 5, the detail could be moved to a location wherethe stress range is smaller.In many structures it may be possible to omit the lateralbracing system in the high stress range regions of the span.Lateral bracing is not required in highway spans up to 125ft long (AAS IlTO) or in railroad deck spans up to 50 ft(AREA). In longer s!,,1ns, a continuous lateral system may notbe required over the full length of the structure.For a more complete discussion of lateral ronnmion details,see Chapter 6.If the attachment were bolted to the nange as in Fig. 3, theallowable stress range: is increased to Category B on the netsection for a bearin -type connection and the gross section fora friction-type connection. This permits a higher allowablestress range than for the welded attachments of Figs. I and 2 .The reduction in net area will only slightly reduce this in·creased ratigue strength .Still another method of increasing the allowable stress rangeis to use attachments with a "radiused" transition, as illustrated in Fig. 4. The weld ends must also be ground smooth
2BridgeFig. I.Fatigue GoodeFIg. J.Brackd atlachf'd ltJ flanl!f' h\ Innglludmal fill lBo/lt'd flange attachmentor gmfJl u't"ld.at the transition radius10accomplish the desired increase.Obviously the machining and grinding required to fabricatesuch delails may be rnor cOSIly Ihan olher mel hods of salisfying Ihe faligue provisions. The AAS IITO, AREA, andAlSC specifications all include radiused transitions in the mostreeent fatigue specifications.If oUl-of-plane forces are 10 be resiSled , as in curv,d girderbridges, Ihe Iransverse Sliffeners can be welded 10 holh nangesat cross bracing to assist in resisting Lhese forces, as in Fig. 5.The resulling delail provides a Calegory C condilion al IhelOp of Ihe nange surface which has a Slress range from S2%to 100% greater than the nange 3n3chmenls shown in Figs.I and 2, depending on Ihe design life.RCote9C)fYR 241"2 4 ,.R 6,n6 R 2in.2 RBC0ENOle The weld end musl be oround smooth of ttw tranSItIOnradiUSfig. 2.Braclul alloc"hed /() f1ang by fillet weldsf ig. 4R adtused I ranjltwn for uoelded f/angt altachmen/jO
Design Detail.32I 4-6h"P E'F,g. 7.TronSt't'ru' and f,mgllu,JlnalJ/llf n,.,.splat I'd on f'l,pOIl/t'utlt') nJuxbIt is Important to rra lize that any detail ca n be used if it isprope rl y acrounted for in the design. The simplest detailconsisten t with the stress requ irements wi ll generally be themOSt desirable from the standpoint of design, fahri alion, andeconomy.W hen tran"e"" and longitudinal stiffeners are used, ea(hprovidn a weld termination, as is illustrated in Fig. 6. in the longitudina l stiffener i, a I()n attachment, the end of thestiffener is governed by the Category E desi n condition Atother points along the stiffener, Category B is applitable Thetransverse stiffener docs nOt provide as \lere a condition,bttaust it is much lihonrr in thr dlrcftion of applard Slrf",.,. Ifboth types of stiffene", are needed III an drea of Sire', r"eKlI,the most desirable fondltinn ( '" Ix- athlt'\ed b\ plann thelongitudinal stiITener on one 'Ide (If thr web and the tran \erYstiffener on the other, '" In h 7, '" that the lon "udlnalwdd can be contlnuou\ and thr longitudinal 'lirfener caneither be terminated In a r(" lOn of low stress ran r or ('()Illpressivc stress, or inrorporate a radiused transition .11 ItsendFillet welds for tranwrfse stiffeners should lx termlnatcdshort of the web-IO-n", e weld, by a diSlanre of at 1 fourand up to six timc\ tht' web thirkness. as illustrated in Figs.2,3,5,6, and 7, and ,hould not he returned around the end,of the stiffener. Failure 10 !rrminme stiffener wtld\ a suitabledistan above the wt'f .n;IIl (, foon('(llOO tan r ult In adv('r;t'behavior. due to reslrainl 'ilresses Inlroducrd by weldshrinkage and possibk rydll" stresses due to transvrrt;('movements durin c;hlJ)plO or hJndlin . Thi is di'it"us.ro Ingrealer detail later. in lht" c.;('( lion dealin with 'i('{oodar,Slresses (Chapter 5).Transverse groove wrlds in rt1(ion . of ndir ttnCaon or LI"f"'; . .reversal are examined by Ilonde'itrufti"e insiXuion , .15 'iJXf·iritd on plans or joh Slxc:irifatlon'i, to inc;urt th H rK(eS\IV('internal dio;;continuitirc; art not prtsent. Improvements in fa·ligue strength can I afhleH"cI by removal of tht wrld rem·.1"lranH 't'rlt'and /orlgllutimaililjjenersforcemem and by appropriiltt transition,,; brtween plates ufdifferent thickness or width . a,,; illustrated in Fi s . R ilnd 91
4Bridge Fatigue GuideNote Weld ground smoofh gIves Category Bi'lJI melGl'a.nd FlushTope' ISlope noGl'eoter timt,"2 MWeb SptoceReQ,WesNDI "TensionRegIOn ofWebManhol eTopNore.onlyR!:2' · O·as requiredby specificationsNOI 9rOCl'ft welds . st,.ss," or. p.",.nchcukw to IdFig. 8. Transvvu groow weldlInUNb and flangeRemoval of the weld reinforcement at the groove welded details shown in Figs. 8 and 9 improves 'he fa'igue design condi,ion from Category C '0 ategory B.",16FIg. 9, Gusset amn«tlon shOWIng a uanety of structural tkulIls Ulttha wlde range offaLlgue strengthsmagnetic particle examinationtodetermine whether or not,here are cracks in 'he welds. Ultrasonic and radiogra phictales practice d s not provide for adjustments infatigue strength for various sizes of internal discontinuities.inspections are not necessary for longitudinal welds. Largeinternal discontinuities that are perpendicular to the appliedstresses will nOl be present, as would be possible withStudies in England by Il amson and OIhers '6,18 have shown,ha, fatigue streng,h can be adjusted to reflee, larger internaltran sverse groove welds. In longitudinal groove welds, 'hemaximum discontinuity perpendicular to 'he applied stressdiscontinuities. Currentlv used weld quality control requiredcannot ex ed the weld size. In transverse groove wdds, lackof penetration, slag inclusions, or orner types of discontinuitiesmay result in di . continuitjes several times larger than tht weldcross section, which is why nondestructive inspection is nec.Unit dby AWand A1\ I ITO tnsures that transve groove weldswill achie,e 'he Category C or B design condi,ion. With thereinforcement removed, alegory B applies. When the weldreinforcement is left in place, ategory'0isapplicabl .Longitudinal welds that are parallel 'he applied stresses,such as 'he web-,o-flange welds in Figs. I ,hrough 7, have ahigh fa'igue strength. Both longitudinal fille, and groove weldsare Ca'egory B details under such circumstances. In both cases'he fatigue strength is based on expected in,ernal discon-tinuities in the web-lO-nangc connection that are perpendicular to the applied Stresses. Examples of discontinuities inthese welds may be in 'he form of porosity, cold laps, slag in-clusions, or other conditions. In such we:lded connections,discontinuities that are parallel to the stress field have no in·fluenee on 'he members' performan,e. This includes lack ofpenetration discontinuities in both fillet and panial penetrationessary.Coverplated beams, such as shown in Fig. 10, result in lowa ll owable slress range (Ca,egory ) at the cover plate ,erminauon. Category B is applicable away from the cover plate endif it is allached by continuous welds. About 'he sa me fatiguestrength is provided with or without transverse end welds. 2'0The end of 'he longiludinal weld allaching 'he cover platethe fl a nge and the toe of the tra nSverse end we ld provideoomparable conditions. Geome,rical changes in the cover pla'eend have lillie innuence on the fatigue strength. For example,tapering the rover plate width, providing a radius at irs end,or o, her variations as illustra,ed in Fig. 1 I all provide a Ca,egory E detaiL ' " These geometrical variations do no' signif-icantly alter the stress concentration at the weld tnd that islongi,udinal welds, slag inclusions, and other comparablediscontinui,ies. The fatigue strenglh is governed by discon,inuities ,ha, are perpendicular the applied stresses, no, bytransverse the applied stresses. Simply altering 'he shapeof th e cover plate end does no' change this condition by a sig-discominuities that are: parallel. 1Ienet, the inspection criterianificant amount.used for fillel welds is equally applicable to longiludinal grooveBack ing ba rs are freq uently used when fab ri caling boxgirders wi,h single-bevel full penetra,ion groove welds for the'0welds. Generall y, this includes a visua l inspection, with some'0
5Design DetailsCover Plate wrth5q.Jae Endseod UpBar -./Ii(a) FuU PenelratlO(l We ld Wit" BaeklnQ BorM jIII(bl Contmuous F lUet WeldsFig . 10BCounplaled beam shoWIng regron of entlealfallgu slussIe) PortlOl Penetrollon Weldweb-to-nange connection. Care should be exercised with theuse or such bars. Ir intermittent fillet welds are used to connectthe backing bar to the web and nange plates, they may providea Category E connection for the tension nange (see Fig. 12a).This con rvati\'e t tmenl or intermittent tack welds renectsthe lack of test data on this type of connection. Further researchis being planned on thIS detail.If backing bar are needed, it is preferable for the connectingwelds to bt- continuous on the tension nange, as illustrated inFig. 12a, so that Category B is applicable. Alternately, intermittent wdds could be used and then removed arter completing the JOint. Intermittent welds can be used in rogionssubjected to compression without any adverse effect on themember deSign Discontinuous backing bars should not beused.ggQQ.(bl(01 (I)(elf-, . r11.The problems associated wi,hha(kin bars can be aVOIdedsome Instan s. when girders ha\'t sufficiently thic:k web ,by using either a paniaJ JXnetration groo\'e wdd or two filletInwelds for the web-,o-nange connection (see Fi . 12b and 12tl.Both of these joints prOVide a Cat 1!ory B connection Filletwelds may not be practicable for many boxes, bt-("au e aeeesmay not penni' the placemen, of some of the IIlside fillet welds.A Single partial penetration groove weld can be providedwithout requiring a backing bar (see A WS Article 2.5 and9. 12). It also permits easy access'he box joints, . inte 'hewelds can be made from outSide 'he boxes Both partIal pen-'0etration groove wdd and twin fillet wdd connections providea Category B connection, which is the same fatigu(' strengthde,ail as 'he full penetra,ion groove weldFloor beam or cross-girder to longi,udlllal girder connec-tions and stringer to rull.lenv;th tross·glrd('r COnnr(110n Jrea category of joints that can provid(' wide variation 10 fati ue6", '.'(J.'Rstrength Floor beams must either pa . 'hrou h the lon i'u dinal gIrders or be attached to ,hem Typical example-, of noor(dlbeam.to- irder connection are ,hown In Fig 13.md 14 .Among the problems of conttrn are th(' continuity or the noorbeam nanges, 'he attachment of the noor beam nan rs '" 'hegirder nan e, term Ina' ion of 'he web-,o-nange welds, and 'heIIIIIaU3C'hment or pa sage or the noor beam ("ompre . sion.".-'\--(hI(IlEnd of COt'er plate details'hrough 'he girder web .If 'he noor beam ,ension nangeISna", epassed over 'he girder,as illustrated in Fig. 13, wide variation in fatigue strength canresult, depending upon how 'he noor beam web-,o-nange
Bridge Fatigue Guide6Shop groove w. ldr--@NOl and GroundFlushIfIjIfOUndf lushr0 0 l0 0000.lFinish ends of flOnQe .10 be or no flol'IQe we ldsJB.II,d f ,.'d,pllee In SInnOtt .IWeb CleO!nol 51'1o . n Floor Beam OfCross GirderFIg. 1,/."'g.I J.Fhw,r beam-to- lrder c01lnecilOn wllh continuoUSjlv)r beam flangeconneaion is treated. The groove weld in th e fl oor beam flangeis either Category B or C, depending on whether or not thereinforcement is removed or left intact. A more critical designcondition is the terminal.on of the web-to-flange connection.Ir these welds terminate, a Category E design condition results,as shown in Fig. 13. Sucil a large reduction in fatigue strengthcan be avoided by providing continuity in the web-to-nangeweld, as shown in the in!-crl. A smooth radiuscd transition inthe noor beam web can be provided at the CUIOut to accommodate the girder nangc.If the noor beam compression nan e is welded to the girderweb as shown in Fig. 13, a Category detail results. This willpenalize the fatigue strength if a hie;h tensile or reversal stressStrl1lger-lo-jloor beam connectIOns wah hIghallowable fatigue strengthrange occurs in the girder web over a large number of cycles.A detail with a higher allowable Slress range will result if thenoor beam nange is passed through a Cutout similar to thatprovided in the noor beam web.A higher allowable stress range can be achieved in thelongitudinal main member if the noor beams are bolted. Thismay be a more desirable design condition if relatively highStress ranges are present. Figu re 14 shows two details thatprovide Category B design conditions at the stringer-noorbeam intersections. In ooth ca s a Category C de ign condition would resulL in the noor beam from the web fillet weldsor welded shear plate.If the cyclic st resses in the girder web are not criticaJ andthe detail show n in Fig. 13 is used ) care shou ld be exercisedin the development of the nangc-to-wcb connection. If largenoor beam nanges are groove welded to opposite sides of theweb plates, shrinkage stresses will be introduced into the webplate which may result in restraint or lamellar Icars in thegirder web.
Design Example.7CHAPTER 2DESIGN EXAMPLESTwo design examples an: summarized to demonstrate:: theapplication of the AASHTO fatigue provisions. One is asimple structure designed by working stress design for stresscycle Case II; the second is a continuous structure proportionedby load faclOr design for stress cycle Case I.Determine Cover Plate Length (Non-cyclic Analysis):Determine theoretical cutoff point of cover plate by findingpoint at which loads can be carried by concrete and steel sectionalone.Stress in bottom fiber of tension flange of rolled beam willprobably be the controlling design criterion at the cover platetermination. Therefore, check bottom nange Stresses at 10thpoints:DESIGN EXAMPLE IDesign lnformation:Stresses in Bollom Flange ofStcol Heam (ksi)I. 90-ft simple span; working stress design2. Composite construction; rolled beam and cover plate3. 8-in. reinforced concrete slab; Ih-in. assumed integralwearing surface not considered for composite properties4. HS20 loading5. Dead Load I: [), 0.85 kips/ lin. ft (weight ofconcrete slab) plus estimated weight of Sled section6. Dead Load 2: D, 0.40 kips/ lin. ft (static loads10lh Point5 (Midspan)43220.719.917.4- I-7.50o (Support)- I-6.76.45.61.32.413.2IL J,-rot.1I18.017.5J 5.515.343.838.629.616. 812.16.900,'-------applied after concrete is cured, carried by composite7.8.9.10.II.D,D,Theoretical cover plate cutoff point (where stress in tensionsection)Girder spacing: 8 [[-0 in.Wheel load distribution factor: S / 5.5Fatigue Case II , AASHTO Article 1.7.2Steel: Fy 50 ksiConcrete: f' 3,000 psi; n 10flange equals
rationale for the stress range concept and lead lO the current specification provisions. Aniele 1.7.2 of the 1977 AASHTO Specifications, and Art. 1.3.13 of the 1977 AREA pecifications and its Commentary,
1 COMPARISON OF ANSI/AISC 360-16 TO ANSI/AISC 360-10 (prepared by Sam Baer and Matthew Troemner) This document summarizes the revisions contained in the 2016 AISC Specification for Structural Steel Buildings (ANSI/AISC 360-16) compared to the 2010 AISC Specification for Structural Steel Buildings (ANSI/AISC 360-10).File Size: 231KB
AISC Design Guide 4: Extended End-Plate Moment Connections Seismic and Wind Applications AISC Design Guide 4 AISC Design Guide 13: Wide-Flange Column Stiffening at Moment Connections AISC Design Guide 13 AISC Steel Construction Manual 13th Edition AISC SCM 13th Ed INPUT Code Reference
WisDOT Bridge Manual Standard Details, July 2012 (WisDOT Standard Details) AISC Specification for Structural Steel Buildings, February 2010 (AISC 360-10) AISC Steel Construction Manual, 14th Edition, 2010 (AISC 14th) NCHRP Report 412: Fatigue-Resistant Design of Cantilevered Signal, Sign and Light Supports (NCHRP 412)
The 2005 Seismic Provisions (ANSI/AISC 341-05) were developed so that the new main AISC Specification (ANSI/AISC 360-05, also completed in 2005) could be used us a primary reference and were referenced in the 2006 IBC. The contents of the previous editions of the AISC Seismic Provisions will be briefly summarized in this paper.
Application of ASME Fatigue Code: 3-F.1 ASME Smooth Bar Fatigue Curves Alternative Effective Stress vs Fatigue Cycles (S-N Curve) With your weld quality level assessed and an accurate FEA stress number, one can use the ASME fatigue curve to calculate the number of Fatigue Cycles. In our prior example, the fatigue stress could be 25.5 ksi or as .
II. AISC Code of Standard Practice for Steel Buildings and Bridges (AISC 303-10) III. RCSC Specification for Structural Joints Using ASTM A325 or A490 Bolts . b) ANSI/AWS D1.1/D.1.1M Structural Welding Code - Steel. c) ANSI/AWS D1.5 Bridge Welding Code. d) AISC 503 Selected ASTM St
Fatigue of reinforcing steel in concrete bridge decks has not been identified as a common failure mode. Generally, the stress range occurring in reinforcing steel is below the fatigue threshold and infinite fatigue life can be expected. Closure pour joints, however, may be vulnerable to fatigue if some specific design details are present.
Recently, we were made aware of some technical revisions that need to be applied to the AASHTO LRFD Bridge Design Specifications, 6th Edition. Please replace the existing text with the corrected text to ensure that your edition is both accurate and current. AASHTO staff sincerely apologizes for any inconvenience.File Size: 2MBPage Count: 104Explore furtherAASHTO LRFD 2012 Bridge Design Specifications 6th Ed ( US .archive.orgAASHTO Issues Updated LRFD Bridge Design Guideaashtojournal.orgAASHTO Publishes New Manual for Bridge Element Inspection .aashtojournal.orgAASHTO LRFD Bridge Design Specifications. Eighth Edition .trid.trb.orgSteel Bridge Design Handbook American Institute of Steel .www.aisc.orgRecommended to you b
