Transient responses of girder bridges with vertical poundings under near-fault vertical earthquake

Previous studies on pounding responses of bridge structures mainly focus on the horizontal pounding between adjacent structures. However, the vertical pounding responses of bridge are rarely studied. The aim of this paper is develop a theoretical approach to investigate the transient behavior of continuous bridge under near-fault vertical ground motions. The transient behavior of bridge manifests as the earthquake-induced response wave and pounding-induced response wave travel throughout bridge. Based on a new continuous model of beam-spring-rod, the theoretical solution of bridge responses involving multiple vertical poundings is derived by the expansion of transient wave functions in a series of eigenfunctions. A new theoretical solving approach of the multiple vertical pounding forces is presented based on the transient internal force on the contact surface of the girder and bearing. The numerical results show that the present method can reasonably capture the propagations of the earthquake-induced response wave and pounding-induced response wave. The calculations of pounding force by the present method are convergence of the time-step size and truncation number of wave modes. As the effect of transient wave is taken into account, the numerical results show several transient phenomena involving the vertical pounding, the high pounding force, the multiple-pounding phenomenon, the vertical separation of girder from the bearing, the dependence of poundings on earthquake period and the narrow period window of poundings. Copyright (c) 2015 John Wiley & Sons, Ltd.