Mechanism Study of Vehicle–Bridge Dynamic Interaction under Near-Fault Ground Motions

The effect of vehicle on the seismic responses of highway bridge has usually been neglected under the assumption that the possibility of vehicles crossing highway bridge or viaduct with a concurrent earthquake is extremely low. Furthermore, there is no in phase movement of vehicle and bridge was observed in past earthquake events. However, in the heavily trafficked urban area this is probably not the case. The mechanism of vehicle–bridge dynamic interaction still remains unclear. Therefore, an analytical vehicle–bridge model with contact elements is built to study the dynamic interaction and the seismic responses of vehicle–bridge system when subjected to near-fault ground motions. In this vehicle–bridge model, vehicle and highway bridge are coupled through Coulomb friction forces in the horizontal directions and through Hertz impact force in the vertical direction, respectively. The horizontal Coulomb friction forces varying with the variation of vertical Hertz impact force under earthquake excitations. Analysis results reveal that vehicle sometimes has a significant influence on the vertical seismic displacement response of bridge and mass ratio of vehicle to bridge is one of the primary factors governing the effect of vehicle on the seismic responses of bridge. Influence of vehicle frequency and damping ratio on the seismic responses of bridge are both related to mass ratio and become significant with the increasing of mass ratio. However, for the responses of the vehicle itself, influence of vehicle frequency and damping ratio is significant only when the mass ratio is small. Due to the weak coupling of vehicle and bridge in the horizontal directions, horizontal displacements of the vehicle can reach several meters, hence possibly endanger the traveling safety of vehicle on highway bridge.