Dynamic response of bridges to multiple truck loading

An analytical procedure called the iterative dynamic substructuring method (IDSM) is described for determining the response of a beam–slab bridge system traversed by multi-axle trucks. The trucks are idealized as systems of beams mounted on springs and the bridge as a grid. The IDSM applies mode superposition analysis to the bridge and truck as separate structures connected only at the time-dependent contact points. The bridge is subjected to forces equal to the time-dependent forces on the truck springs, while the truck is subjected to “ground” motion displacements. Since the forces in the spring and the ground motion are interdependent, an iterative procedure is necessary to achieve compatibility of forces and displacements at the contact points.The IDSM is employed to study the response to multiple vehicle loading of the Conestogo River bridge which was field tested by the Ontario Ministry of Transportation and Communications. The purpose of the analysis is to compare single with multiple vehicle loadings under various conditions of truck speeds and positions. The results are used to assess the validity of the reduction in impact factors applied to multiple vehicle loading in the Ontario Bridge Code.