Draft
2.5OtherImportant Considerations 49
2.4.3 BridgeLoads
For highway bridges,designloadsaregivenby theAASHTO(Associationof AmericanState
Highway TransportationOcials). TheHS-20truck is usedforthedesignof bridgesonmain
highways,Fig.6.3. Eitherthedesigntruck withspeci edaxleloadsandspacingmustbe used
ortheequivalent uniformloadandconcentratedload.Thisloadingmustbe placedsuch that
maximumstressesareproduced.
Figure2.11:Truck Load
2.4.4 ImpactLoad
2.5 OtherImportant Considerations
2.5.1 LoadCombinations
45 Live loadsspeci edby codesrepresent themaximumpossibleloads.
46 Thelikelihood of alltheseloadsoccurringsimultaneouslyis remote.Hence,buildingcodes
allow certainreductionwhencertainloadsarecombinedtogether.
47 Furthermore,structuresshouldbe designedto resistacombinationof loads.
48 DenotingD=dead;L=live; Lr=roof live; W=wind;E=earthquake; S=snow;T=tem-
perature;H=soil:
49 For theloadandresistancefactordesign(LRFD)method of concretestructures,theAmeri-
canConcreteInstitute(ACI)Buildingdesigncode (318)(318n.d.)requiresthatthefollowing
loadcombinationsbe considered:
- 1.4D+1.7L