Dynamic Responses of RC Girder Bridge under Heavy Truck and Seismic Loads Combined

Overloaded truck and earthquake have become two main factors responsible for bridge damage, consequently the combination of heavy truck and seismic loads as a typical occurrence of extreme events is likely to lead to bridge collapse or destructive damage, in which the crucial issues of coupling load model, dynamic equations and bridge responses have not been adequately addressed. In this study, a simplified vehicle-bridge model consisting of many containers is established to simulate vehicle passage, and the dynamic equations are derived for a 5-axle truck on a simply supported beam as an illustration. Then, five ground motions selected from PEER with appropriate peak ground accelerations and durations and the three truck models specified in American Association of State Highway and Transportation Officials, Caltrans and Chinese codes are applied on the finite element model of a typical reinforced concrete continuous girder bridge, in which, vehicle speed, number of trucks, ground motion and vehicle type are assumed to be random variables and their influences on dynamic responses of the bridge are analyzed. The results show seismic load is the governing factor in dynamic responses but truck load may change displacement shapes; in addition, dynamic responses present a high sensitivity with the number of trucks (set as truck platoon) and gross vehicle weight but rare with vehicle speed. Specifically, the presence of a few trucks could serve as energy dissipation facilities for the bridge under seismic motions but may amplify the response when more trucks involved; some combinations of truck platoon with seismic excitation produce very large displacements and even cracks on the bridge, therefore, such an extreme event requires higher robustness in bridge design to make it be sustainable and serviceability after earthquakes.