Elasto-Plastic Seismic Response of RC Continuous Bridge with Foundation-Pier Dynamic Interaction

Abstract

In civil engineering projects, shallow foundation is often employed as a base for bridges, wind-turbines, oil tanks and so on. But shallow foundation experiences obvious uplift and plastic deformation under intensive earthquake action. Existing solution to the problem relies on the study of soil-structure interaction (SSI) aiming at the nonlinear performance of soil foundation rather than at a coupled bridge-foundation system. To save the situation, this paper presents a two-degree of freedom (2DOF) model, considering nonlinearities of both RC pier and soil foundation, to evaluate seismic responses of a bridge-foundation system. The 2DOF model provides equations of motion to calculate constant damping effect and the time-varying damping effect, respectively. In addition, the revised Winkler foundation model, considering nonlinear bending moment versus rotation, is used to study plasticity and uplift effects of soil foundation, the modified Takeda hysteretic model is employed to simulate the nonlinear performance of RC bridge piers, and the numerical simulation of a typical RC continuous bridge with shallow foundation in four ground motions and incremental seismic intensities is conducted to assess the seismic performance of the bridge-foundation system. According to the results from these studies, the 2DOF model, truly reflecting the nonlinear properties of both RC pier and soil foundation, is proved more reasonable than the existing SDOF model for overestimating the seismic response of the bridge-foundation system. Moreover, the ratio of the moment resist stiffnesses of the RC pier and the soil-foundation is a critical factor affecting the seismic behavior and the time-varying damping, favorable in dissipating earthquake energy but unfavorable in limiting the displacement response at top of the pier.