Multiple Presence Factor for Truck Load on Highway Bridges

Abstract

Trucks may simultaneously appear on a highway bridge in the same lane or different lanes, which represent the governing load for short- and medium-span bridges. In practice specifications, the multiple presence factor (MPF) to cover these simultaneous loads was developed using in- tuitionormodelswithoutsupportofmeasuredweightdataoftrucksinmotion.ThispaperpresentsaresearcheffortofderivingaMPFbasedonweigh- in-motion(WIM)truck data, forboththestrengthandfatiguelimitstates,includingabout 68milliontrucksgathered for436monthsandfrom 43 sites in California, Oregon, Michigan, and New York. The resulting MPFs are proposed in this paper as functions of bridge-span length, truck-traffic vol- ume, and number of lanes available. They show that the code-specified MPF values are conservative and sometimes overconservative by 400% or more, which may have caused too high requirements for load-rating existing bridges, especially for shorter spans and low truck traffic. The recom- mended MPF may be considered to be adopted in specifications for highway bridge design and evaluation. This paper also presents a new truck-by- truckanalysisapproachforunderstandingtheloadeffectof trucks in motion,takingadvantageof increasinglyavailableWIMdataof largequantityto avoidunsupportedassumptionsinlive-loadmodeling.DOI:10.1061/(ASCE)BE.1943-5592.0000330.©2013 American Society of Civil Engineers. CE Database subject headings: Trucks; Maximum loads; Fatigue; Highway bridges; Design. Author keywords: Truck load; Maximum load; Fatigue load; Highway bridge; Design and evaluation; Multiple presence.