chapter 3 loads contents - washington state … 3 loads contents. contents page 3-ii wsdot bridge...

WSDOT Bridge Design Manual M 23-50.17 Page 3-i June 2017

3.1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-1

3.2 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-2

3.3 LoadDesignations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-3

3.4 LimitStates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-4

3.5 LoadFactorsandLoadCombinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-53.5.1 Load Factors for Substructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-6

3.6 LoadsandLoadFactorsforConstruction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-7

3.7 LoadFactorsforPost-tensioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-83.7.1 Post-tensioningEffectsfromSuperstructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-83.7.2 SecondaryForcesfromPost-tensioning,PS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-8

3.8 PermanentLoads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-93.8.1 DeckOverlayRequirement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-9

3.9 LiveLoads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-103.9.1 Design Live Load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-103.9.2 LoadingforLiveLoadDeflectionEvaluation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-103.9.3 DistributiontoSuperstructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-103.9.4 Bridge Load Rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-13

3.10 PedestrianLoads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-14

3.11 WindLoads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-153.11.1 WindLoadtoSuperstructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-153.11.2 Wind Load to Substructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-153.11.3 Wind on Noise Walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-15

3.12 LoadsonCulverts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-16

3.13 EarthquakeEffects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-17

3.14 EarthPressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-18

3.15 ForceEffectsDuetoSuperimposedDeformations . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-19

3.16 OtherLoads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-203.16.1 Buoyancy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-203.16.2 Collision Force on Bridge Substructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-203.16.3 CollisionForceonTrafficBarrier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-203.16.4 ForcefromStreamCurrent,FloatingIce,andDrift . . . . . . . . . . . . . . . . . . . . . . . . . . .3-203.16.5 IceLoad . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-203.16.6 UniformTemperatureLoad . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-20

3.99 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-21

Chapter 3 Loads Contents

Contents

Page 3-ii WSDOT Bridge Design Manual M 23-50.17 June 2017

WSDOT Bridge Design Manual M 23-50.17 -1 June 2017

Chapter 3 Loads

3.1 ScopeAASHTO Load and Resistance Factor Design (LRFD) Specifications shall be the minimumdesigncriteriausedforallbridgesexceptasmodifiedherein.

Loads Chapter 3

Page 3-2 WSDOT Bridge Design Manual M 23-50.17 June 2017

3.2 DefinitionsThedefinitionsinthissectionsupplementthosegiveninLRFDSection3.

Permanent Loads –Loadsandforcesthatare,orareassumedtobe,eitherconstantuponcompletionofconstructionorvaryingonlyoveralongtimeinterval.

Transient Loads –Loadsandforcesthatcanvaryoverashorttimeintervalrelativetothelifetimeofthestructure.

Chapter 3 Loads

WSDOT Bridge Design Manual M 23-50.17 Page 3-3 June 2017

3.3 LoadDesignationsLoad designations follow LRFD Article 3.3.2.

Loads Chapter 3


3.4 LimitStatesThebasiclimitstateequationgivenbyLRFD1.3.2.1isas:

ΣηiγiQi≤φRn = Rr (3 .4-1)

Where:ηi = loadmodifierγi = load factorQi = forceeffectφ = resistance factorRn = nominalresistanceRr = factored resistance

Themodifier,ηiistheproductoffactorsforductility,redundancy,andimportance.Forsimplicityuseavalueof1.0forηiexceptforthedesignofcolumnswhenaminimumvalue of γiisappropriate.Insuchacase,useηi=0.95.Compressionmembersinseismicdesignsareproportionedanddetailedtoensurethedevelopmentofsignificantandvisibleinelasticdeformationsattheextremeeventlimitstatesbeforefailure.

StrengthIVloadcombinationshallnotbeusedforfoundationdesign.

TheloadfactorforliveloadintheServiceIIIloadcombinationshallbeasspecifiedin Section 3.5.

Chapter 3 Loads


3.5 LoadFactorsandLoadCombinationsThelimitstatesloadcombinations,andloadfactors(γi) used for structural design are in accordance with the AASHTOLRFDTable3.4.1-1.Forfoundationdesign,loadsarefactoredafterdistributionthroughstructuralanalysisormodeling.

ThedesignliveloadfactorfortheServiceIIILimitStateloadcombinationshallbeasfollows:

γLL=0.8whentherequirementsofSections5.6.1 and 5.6.2aresatisfiedandstressanalysisisbasedongrosssectionproperties.

γLL=1.0whentherequirementsofSections5.6.1 and 5.6.2aresatisfiedandstressanalysisisbasedontransformedsectionproperties.

InspecialcasesthatdeviatefromtherequirementsofSections5.6.1 and 5.6.2 and have beenapprovedbytheWSDOTBridgeDesignEngineer,γLL,shallbeasspecifiedintheAASHTO LRFD.

TheServiceIIIliveloadfactorforloadratingshallbe1.0.

TheliveloadfactorforExtremeEvent-ILimitStateloadcombination,γEQ as specifiedintheAASHTOLRFDTable3.4.1-1forallWSDOTbridgesshallbetakenequal to 0.50. The γEQfactorappliestotheliveloadforceeffectobtainedfromthebridgeliveloadanalysis.Associatedmassofliveloadneednotbeincludedinthedynamicanalysis.

TheAASHTOLRFDallowtheliveloadfactorinExtremeEvent-Iloadcombination,γEQ,bedeterminedonaprojectspecificbasis.Thecommentaryindicatesthatthepossibilityofpartialliveload,i.e.,γEQ<1.0,withearthquakesshouldbeconsidered.TheapplicationofTurkstra’sruleforcombininguncorrelatedloadsindicatesthatγEQ =0.50isreasonableforawiderangeofvaluesofaveragedailytrucktraffic(ADTT).TheNCHRPReport489recommendsliveloadfactorforExtremeEvent-ILimitState,γEQ equal to 0.25 for all bridges. This factor shall be increased to γEQ equal to 0.50 for bridgeslocatedinmainstateroutesandcongestedroads.

Sincethedeterminationofliveloadfactor,γEQ based on ADTT or based on bridges locatedincongestedroadscouldbeconfusingandquestionable,itisdecidedthatliveload factor of γEQ equal to 0.50 to be used for all WSDOT bridges regardless the bridge location or congestion.

Thebaseconstructiontemperaturemaybetakenas64°FforthedeterminationofTemperatureLoad.

The load factors γTG and γSEaretobedeterminedonaprojectspecificbasisinaccordance with Articles 3.4.1 and 3.12 of the AASHTO LRFD. Load Factors for PermanentLoads,γpareprovidedinAASHTOLRFD Table 3.4.1-2.

TheloadfactorfordowndragloadsshallbeasspecifiedintheAASHTOLRFD Table 3.4.1-2.TheGeotechnicalReportwillprovidethedowndragforce(DD). The down dragforce(DD)isaloadappliedtothepile/shaftwiththeloadfactorspecifiedintheGeotechnicalReport.Generally,liveloads(LL) are less than the down drag force and shouldbeomittedwhenconsideringdowndragforces.

Loads Chapter 3


TheLoadFactorsforSuperimposedDeformationsareprovidedinTable 3.5-3 below.

PS CR,SHSuperstructure 1 .0 1 .0

Substructures that are fixed at the base and have a longitudinal connection with the superstructure

(such as a hinged or integral connection) and analyzed using the gross moment of inertial (Ig)

0 .5 0 .5

All other substructure supporting Superstructure analyzed using either gross moment of inertia (Ig) or the effective

cracked moment of inertia (Ieffective)1 .0 1 .0

LoadFactorsforSuperimposedDeformationsTable 3.5-3

3.5.1 Load Factors for SubstructureTable 3.5-4belowprovidesgeneralguidelinesforwhentousethemaximumorminimumshaft/pile/columnpermanentloadfactorsforaxialcapacity,uplift,andlateral loading.

Ingeneral,substructuredesignshoulduseunfactoredloadstoobtainforcedistributioninthestructure,andthenfactortheresultingmomentandshearforfinalstructuraldesign.Allforcesandloadfactorsareasdefinedpreviously.

AxialCapacity Uplift LateralLoadingDCmax, DWmax DCmin, DWmin DCmax, DWmax

DCmax, DWmax for causing shear DCmax, DWmax for causing shear DCmax, DWmax causing shear

DCmin, DWmin for resisting shear DCmin, DWmin for resisting shear DCmin, DWmin resisting shear

DCmax, DWmax for causing moments



DCmin, DWmin for resisting moments



EVmax EVmin EVmax

DD = varies DD = varies DD = varies

EHmax EHmax if causes uplift EHmax

Minimum/MaximumSubstructureLoadFactorsforStrengthLimitStateTable 3.5-4

Inthetableabove,“causingmoment”and“causingshear”aretakentobethemomentandshearcausingaxial,uplift,andlateralloadingrespectively.“Resisting”istakingtomeanthoseforceeffectsthatarediminishingaxialcapacity,uplift,andlateralloading.

Chapter 3 Loads


3.6 LoadsandLoadFactorsforConstructionUnlessotherwisespecified,theloadfactorforconstructionloadsandforanyassociateddynamiceffectsshallnotbelessthan1.5inStrengthI.TheloadfactorforwindinStrengthIIIshallnotbelessthan1.25.

WheninvestigatingStrengthLoadCombinationsI,III,andVduringconstruction,loadfactorsfortheweightofthestructureandappurtenances,DC and DW,shallnot be taken to be less than 1.25.

Whereevaluationofconstructiondeflectionsarerequiredbythecontractdocuments,LoadCombinationServiceIshallapply.Constructiondeadloadsshallbeconsideredaspartofthepermanentloadandconstructiontransientloadsconsideredpartoftheliveload.Theassociatedpermitteddeflectionsshallbeincludedinthecontractdocuments.

Forfalseworkandformworkdesignloads,seeStandard Specifications Section6-02.3(17)A.Thebaseconstructiontemperatureshallbetakenas64°FforthedeterminationofTemperatureLoad.

Loads Chapter 3


3.7 LoadFactorsforPost-tensioning3.7.1 Post-tensioningEffectsfromSuperstructure

Whencast-in-place,post-tensionedsuperstructureisconstructedmonolithicwiththepiers,thesubstructuredesignshouldtakeintoaccountframemomentsandshearscausedbyelasticshorteningandcreepofthesuperstructureuponapplicationoftheaxialpost-tensioningforceatthebridgeends.Framemomentsandshearsthusobtainedshouldbeaddedalgebraicallytothevaluesobtainedfromtheprimaryandsecondarymomentdiagramsappliedtothesuperstructure.

Whencast-in-place,post-tensionedsuperstructurearesupportedonslidingbearingsatsomeofthepiers,thedesignofthosepiersshouldincludethelongitudinalforcefromfrictiononthebearingsgeneratedasthesuperstructureshortensduringjacking.Whenpost-tensioningiscomplete,thefullpermanentreactionfromthiseffectshouldbeincludedinthegoverningAASHTOloadcombinationsforthepierunderdesign.

3.7.2 SecondaryForcesfromPost-tensioning,PSTheapplicationofpost-tensioningforcesonacontinuousstructureproducesreactionsatthestructure’ssupportandinternalforcesthatarecollectivelycalledsecondary forces.

Secondaryprestressingforces(i.e.secondarymoments)aretheforceeffectsincontinuousmembers,asaresultofcontinuouspost-tensioning.Inframeanalysissoftware,thesecondarymomentsaregenerallyobtainedbysubtractingtheprimarymoment(P*e)fromthetotalPSmomentobtainedbyapplyinganequivalentstaticloadwhichrepresentstheforcesduetopost-tensioning.Aloadfactor,γPS,of1.0isappropriateforthesuperstructure.Forfixedcolumnsa50percentreductioninPSforceeffectscouldbeusedgiventheelasto-plasticcharacteristicsofthesoilsurroundingthefoundationelements.

Chapter 3 Loads


3.8 PermanentLoadsThedesignunitweightsofcommonpermanentloadsareprovidedinTable 3.8-1.

Item LoadPrecast Pre-tensioned or Post-tensioned Spliced Girders 165 lb/ft3

All Other Normal-Weight Reinforced Concrete 155 lb/ft3

Unreinforced Concrete 145 lb/ft3

Concrete Overlay 150 lb/ ft3

Stay-in-Place Form for Box Girder (applied to slab area less overhangs and webs) 5 lb/ft2

Traffic Barrier (32″ – F Shape) (Normal weight concrete) 460 lb/ftTraffic Barrier (42″ – F Shape) (Normal weight concrete) 710 lb/ftTraffic Barrier (34″ – Single Slope) (Normal weight concrete) 490 lb/ftTraffic Barrier (42″ – Single Slope) (Normal weight concrete) 670 lb/ftWearing Surface – Hot Mix Asphalt (HMA)/Asphalt Concrete Pavement (ACP) 140 lb/ft3

Soil, Compact 125 lb/ft3

Prestressed Concrete 165 lb/ft3

Light Weight Aggregate Concrete 125 lb/ft3

PermanentLoadsTable 3.8-1

Forlightweightconcretebarrier,multiplythenormalweightconcretebarrierweightfromTable 3.8-1by(125/155).

3.8.1 DeckOverlayRequirementVehiculartrafficwillgeneratewearandruttingonaconcretebridgedeckoverthelifeofabridge.OneoptiontocorrectexcessivewearistoaddaHotMixAsphalt(HMA)overlayontopoftheexistingconcretedeck.Thistypeofoverlayrequireslessconstructiontimeandislessexpensivecomparedtoremovingaportionofthedeckandaddingamodifiedconcreteoverlay.Theinitialbridgedesignneedstoincorporatethe future overlay dead load.

ConcretebridgedeckprotectionsystemsshallbeinaccordancewithSection 5.7.4 for newbridgeconstructionandwideningprojects.Toaccommodateafuturedeckoverlay,bridges shall be designed as shown Table 3.8-2 below.

Loads Chapter 3


3.9 LiveLoads3.9.1 Design Live Load

Liveloaddesigncriteriaarespecifiedinthelowerrightcornerofthebridgepreliminaryplansheet.TheBridgePreliminaryPlanEngineerdeterminesthecriteriausingthefollowingguideline:• New bridges and Bridge widening with addition of substructure – HL-93• Bridgesuperstructurewideningwithnoadditionofsubstructure–Liveloadcriteria

of the original design• Detourandothertemporarybridges–75percentofHL-93

TheapplicationofdesignvehicularliveloadsshallbeasspecifiedinAASHTOLRFD3.6.1.3.Thedesigntandem,or“lowboy”,definedinLRFDC3.6.1.1shall be included in the design vehicular live load.

TheeffectofonedesigntandemcombinedwiththeeffectofthedesignlaneloadspecifiedinLRFDArticle3.6.1.2.4and,fornegativemomentbetweenthepointsofcontraflexureunderauniformloadonallspansandreactionsatinteriorsupports,shallbeinvestigatedadualdesigntandemspacedfrom26.0feetto40.0feetapart,measuredbetweenthetrailingaxleoftheleadvehicleandtheleadaxleofthetrailingvehicle,combinedwiththedesignlaneload.Forthepurposeofthisarticle,thepairsofthedesigntandemshallbeplacedinadjacentspansinsuchpositiontoproducemaximumforceeffect.Axlesofthedesigntandemthatdonotcontributetotheextremeforceeffectunderconsiderationshallbeneglected..

3.9.2 LoadingforLiveLoadDeflectionEvaluationTheloadingforliveloaddeflectioncriteriaisdefinedinLRFDArticle3.6.1.3.2.LiveloaddeflectionsfortheServiceIlimitstateshallsatisfytherequirementsofLRFD Section 2.5.2.6.2.

3.9.3 Distribution to SuperstructureA. Multi Girder Superstructure

Theliveloaddistributionfactorforexteriorgirderofmultigirderbridgesshallbeasfollows:• Forexteriorgirderdesignwithslabcantileverlengthequalorlessthan40percentoftheadjacentinteriorgirderspacing,usetheliveloaddistributionfactorforinteriorgirder.Theslabcantileverlengthisdefinedasthedistancefromthecenterlineoftheexteriorgirdertotheedgeoftheslab.

• Forexteriorgirderdesignwithslabcantileverlengthexceeding40percentoftheadjacentinteriorgirderspacing,usetheleverrulewiththemultiplepresencefactorof1.0forsinglelanetodeterminetheliveloaddistribution.Theliveloadusedtodesigntheexteriorgirdershallnotbelessthantheliveloadusedfortheadjacentinteriorgirder.

• ThespecialanalysisbasedontheconventionalapproximationofloadsonpilesasdescribedinLRFDArticleC4.6.2.2.2dshallnotbeusedunlesstheeffectivenessofdiaphragmsonthelateraldistributionoftruckloadis investigated.

Chapter 3 Loads


B. Concrete Box Girders

Theloaddistributionfactorformulti-cellcastinplaceconcreteboxgirdersshallbeperAASAHTOLRFDforinteriorgirdersfromTable4.6.2.2.2b-1forbendingmoment,andTable4.6.2.2.3a-1forshear.Theliveloaddistributionfactorforinteriorgirdersshallthenbemultipliedbythenumberofwebstoobtainthedesignliveloadfortheentiresuperstructure.Theliveloaddistributionneednotexceedthetotalnumberofdesignlanes. The correction factor for live load distribution forskewedsupportasspecifiedinTables4.6.2.2.2e-1forbendingmomentand4.6.2.2.3c-1 for shear shall be considered.

DF = Nb xDfiLiveloaddistributionfactorformulti-cellboxgirder (3 .9 .4-1)Where:

Dfi = Live load distribution factor for interior web Nb = Numberofwebs

C. Multiple Presence Factors

Areductionfactorwillbeappliedinthesubstructuredesignformultipleloadingsin accordance with AASHTO.

D. Distribution to Substructure

Thenumberoftrafficlanestobeusedinthesubstructuredesignshallbedeterminedbydividingtheentireroadwayslabwidthby12.Nofractionallanesshallbeused.Roadwayslabwidthsoflessthan24feetshallhaveamaximumoftwo design lanes.

E. Distribution to Crossbeam

Thedesignandloadratingliveloadingisdistributedtothesubstructurebyplacingwheellinereactionsinlaneconfigurationsthatgeneratethemaximumstressinthe substructure. A wheel line reaction is one-half of the reaction of a single lane ofliveload.Forintegralandhingedcontinuitydiaphragms,liveloadsareconsid-ered to act directly on the substructure without further distribution through the superstructureasillustratedinFigure 3.9-1.Forgirderconfigurationswherethereisaclearloadpaththroughthegirderstothecrossbeam,suchasatexpansionpierswithgirderssupportedonindividualbearings,liveloadreactionsareappliedthroughthebearings.Normally,substructuredesignwillnotconsiderliveloadtorsionorlateraldistribution.Sideswayeffectsshallbetakenintoaccount.

Loads Chapter 3


WHEEL LINE LOADS APPLIEDTO SUPERSTRUCTURE

WHEEL LINE LOADS APPLIEDTO SUBSTRUCTURE

CROSSBEAM

CROSSBEAM

LIVE LOAD ON BRIDGE SECTION

LiveLoadDistributiontoSubstructureFigure 3.9-1

Forsteelandprestressedconcretesuperstructurewheretheliveloadistransferredtosubstructurethroughbearings,crossframesordiaphragms,thegirderreactionmaybeusedforsubstructuredesign.Liveloadplacementisdependentonthememberunderdesign.Someexamplesofliveloadplacementareasfollows.Theexteriorvehiclewheelisplaced2feetfromthecurbformaximumcrossbeamcantilevermomentormaximumeccentricfoundationmoment.

Forcrossbeamdesignbetweensupports,thelanesareplacedtoobtainthemaximumpositivemomentinthemember;thenre-locatedtoobtainthemaximumshearornegativemomentinthemember.

Forcolumndesign,thedesignlanesareplacedtoobtainthemaximumtransversemomentatthetopofthecolumn;thenre-locatedtoobtainthemaximumaxialforceofthecolumn.

Chapter 3 Loads


3.9.4 Bridge Load RatingBridgedesignersareresponsibleforDesign,Legal,andPermitloadratingofnewbridgesinaccordancewiththeNationalBridgeInspectionStandards(NBIS)andtheAASHTO Manual Bridge Evaluation. See Chapter13 fordetailedinformationonloadingrequirementsforbridgeloadrating.

SuperstructureTypeConcreteCover

Overlayshownintheplan

FutureDesignOverlay

DeckProtectionSystems1and4:• Precast concrete, steel I or box girder

with cast-in-place slab• Precast slabs with cast-in-place slab• Reinforced and post-tensioned box

beams and slab bridges• Mainline Bridges on State Routes

2½″ (Including ½″ wearing

surface)None 2″ HMA

DeckProtectionSystems1and4:• Undercrossing bridge that carries traffic

from a city street or county road• Bridges with raised sidewalks

2½″ (Including ½″ wearing

surface)None None

DeckProtectionSystem2:• Concrete Overlays

Varies Varies None

DeckProtectionSystem3:• HMA Overlays

Varies Varies None

DeckProtectionSystem5:• Segmental bridges• Bridge Decks with longitudinal or

transverse post-tensioning

1¾″ (Including ¼″ wearing

surface)

1½″ Modified Concrete Overlay

None

BridgeOverlayRequirementsTable 3.8-2

Theeffectofthefuturedeckoverlayongirderscamber,“A”dimension,creep,andprofilegradeneednotbeconsideredinsuperstructuredesign.

Deckoverlaymayberequiredatthetimeoforiginalconstructionforsomebridgewideningorstagedconstructionprojectsifridequalityisamajorconcern.

Loads Chapter 3


3.10 PedestrianLoadsPedestrianbridgesshallbedesignedinaccordancewiththerequirementsoftheAASHTO LFRD Guide Specifications for the Design of Pedestrian Bridges,datedDecember2009.

SeismicdesignofpedestrianbridgesshallbeperformedinaccordancewiththerequirementsoftheAASHTOSEISMIC.

PedestrianliveloadonvehicularbridgeshallbeasspecifiedinLRFD3.6.1.6.

Chapter 3 Loads


3.11 WindLoads3.11.1 Wind Load to Superstructure

Fortheusualgirderandslabbridgeshavingindividualspanlengthofnotmorethan150ftandamaximumheightof33feetabovelowgroundorwaterlevel,thefollowingsimplifiedwindpressureonstructure(WS),couldbeusedinlieuofthegeneralmethoddescribedinAASHTOLRFDArticle3.8.1.2:

Limit State

WindExposureCategoryB C D

Transverse Longitudinal Transverse Longitudinal Transverse LongitudinalStrength III 0 .029 0 .007 0 .040 0 .010 0 .046 0 .012Strength V 0 .021 0 .005 0 .021 0 .005 0 .021 0 .005Service I 0 .016 0 .004 0 .016 0 .004 0 .016 0 .004

Service IV 0 .016 0 .004 0 .023 0 .006 0 .026 0 .007

WindPressure(kippersquarefoot)Table3.11.1-1

Bothforcesshallbeappliedsimultaneously.

Fortheusualgirderandslabbridgeshavingindividualspanlengthofnotmorethan150feetandamaximumheightof33feetabovelowgroundorwaterlevel,thefollowingsimplifiedwindpressureonvehicle(WL),couldbeusedinlieuofthegeneralmethoddescribedinAASHTOLRFDArticle3.8.1.3:• 0.10kipperlinearfoot,transverse• 0.04kipperlinearfoot,longitudinal

Bothforcesshallbeappliedsimultaneously.

3.11.2 Wind Load to SubstructureWindforcesshallbeappliedtothesubstructureunitsinaccordancewiththeloadingsspecifiedinAASHTO.Transversestiffnessofthesuperstructuremaybeconsidered,asnecessary,toproperlydistributeloadstothesubstructureprovidedthatthesuperstructureiscapableofsustainingsuchloads.Verticalwindpressure,perAASHTOLRFDSection3.8.2,shallbeincludedinthedesignwhereappropriate,forexample,onsinglecolumnpiers.Windloadsshallbeappliedthroughshearkeysorotherpositivemeansfromthesuperstructuretothesubstructure.Windloadsshallbedistributedtothepiersandabutmentsinaccordancewiththelawsofstatics.Transversewindloadscanbeapplieddirectlytothepiersassumingthesuperstructuretoactasarigidbeam.Forlargestructuresamoreappropriateresultmightbeobtainedbyconsideringthesuperstructuretoactasaflexiblebeamonelasticsupports.

3.11.3 Wind on Noise WallsWindonNoiseWallsshallbeasspecifiedinLRFD3.8.1,3.8.1.2.4,and15.8.2.

Loads Chapter 3


3.12 LoadsonCulvertsLoads and live load distributions on culverts shall be in accordance with the requirementsoftheAASHTOLRFD.SeismicloadingshallbeanalyzedaccordingtoFHWA-NHI-10-034“Technical Manual for Design and Construction of Roadway Tunnels – Civil Elements”.

Chapter 3 Loads


3.13 EarthquakeEffectsEarthquake loads see Chapter4.

Loads Chapter 3


3.14 EarthPressureEarth Pressure loads see Chapter7.

Chapter 3 Loads


3.15 ForceEffectsDuetoSuperimposedDeformationsPS,CR,SH,TUandTGaresuperimposeddeformations.LoadfactorsforPS,CR,and SH,areasshowninTable 3.5-3.Innon-segmentalstructures:PS,CR, and SH aresymbolicallyfactoredbyavalueof1.0inthestrengthlimitstate,butareactuallydesignedforintheservicelimitstate.Forsubstructureinthestrengthlimitstate,thevalue of 0.50 for γPS,γCR,γSH,andγTUmaybeusedwhencalculatingforceeffectsinnon-segmentalstructures,butshallbetakeninconjunctionwiththegrossmomentofinertiainthecolumnsorpiers.Thelargerofthevaluesprovidedforloadfactorof TUshallbeusedfordeformationsandthesmallervaluesforallothereffects.ThecalculationofdisplacementsforTUloadsutilizesafactorgreaterthan1.0toavoidundersizingjoints,expansiondevices,andbearings.

The current AASHTO LRFD require a load factor of 1.2 on CR,SH,andTU deformations,and0.5onotherCR/SH/TUforceeffects.Thelowervaluehadbeenrationalizedasdissipationoftheseforceeffectsovertime,particularlyinthecolumnsandpiers.

Changingtheloadfactorsforcreepandshrinkageisnotstraight-forwardbecauseCR,SHare“superimposeddeformations”,thatis,forceeffectsduetoachangeinmaterialbehaviorthatcauseachangeinthestaticalsystem.Forsafetyandsimplicityindesign,theyaretreatedasloads--despitenotbeingmeasurableattimet=0.However,behaviorisnonlinearandapplicationoftheloadfactormustalsobeconsidered.Somesoftwarewillrunserviceloadanalysistwice:oncewithandoncewithoutCR,SH effects.TheCR and SH can then be isolated by subtracting the results of the two runs. OthersoftwarewillcoupletheCR and SHwiththedeadload,givingashrinkage-orcreep-adjusteddeadload.

Theproposedcompromiseistoassigncreepandshrinkagethesameloadfactorasthe DCloads,butpermitafactorof1.0iftheproject-specificcreepcoefficientcanbedeterminedandisthenusedinthelinearanalysissoftware.

Thermalandshrinkageloadingsareinducedbymovementsofthestructureandcanresultfromseveralsources.Movementsduetotemperaturechangesarecalculatedusingcoefficientsofthermalexpansionof0.000006feet/footperdegreeforconcreteand0.0000065feet/footperdegreeforsteel.Reinforcedconcreteshrinksattherateof0.0002feet/foot.

Loads Chapter 3


3.16 OtherLoads3.16.1 Buoyancy

Theeffectsofsubmergenceofaportionofthesubstructureistobecalculated,bothfordesigningpilingforupliftandforrealizingeconomyinfootingdesign.

3.16.2 Collision Force on Bridge SubstructureSee AASHTO LRFD Articles 3.6.5 and 3.14

3.16.3 CollisionForceonTrafficBarrierSee AASHTO LRFD Article 3.6.5.1

3.16.4 ForcefromStreamCurrent,FloatingIce,andDriftSee AASHTO LRFD Article 3.9

3.16.5 IceLoadInaccordancewithWSDOTHQHydraulicsOfficecriteria,anicethicknessof12″shallbeusedforstreamflowforcesonpiersthroughoutWashingtonState.

3.16.6 UniformTemperatureLoadThedesignthermalmovementassociatedwithauniformtemperaturechangemaybecalculatedusingtherangesoftemperatureasspecifiedherein.Thetemperaturerangesshownbelowreflectthedifferencebetweentheextendedlowerandupperboundarytobeusedtocalculatethermaldeformationeffects.• ConcreteBridges(AllRegions): 0°to100°• SteelBridges(EasternWashington): −30°to120°• SteelBridges(WesternWashington): 0°to120°

Chapter 3 Loads


3.99 References1. AASHTO LRFD Bridge Design Specifications for Design of Highway Bridges,

7th Edition.

Loads Chapter 3


chapter 3 loads contents - washington state … 3 loads contents. contents page 3-ii wsdot bridge...

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