Multi-hazard Damage Analysis of Self-centering Versus Monolithic Bridge Columns Subjected to Combined Seismic and Impact Loading

In this study, a simplified modeling for capturing the interaction between impacting objects and bridge columns based on Hertz contact law have been proposed and implemented in OpenSees. In the proposed model, a compression-only bilinear spring based on Hertz contact law with an initial gap was utilized to simulate the contact stiffness, contact damping, and kinematic response of impact object. The previous impact tests were employed to validate the proposed modeling method. Comparisons between the experimental and numerical results indicate that the modified impact model was able to capture the impact force more accurately than the classic Kelvin model. On this basis, a conventional monolithic bridge column (CMBC) was selected as the prototype bridge, while the corresponding self-centering bridge columns (SCBC) was designed according to equivalent bearing capacity. The seismic and impact hazards were considered as the independent multi-hazard effect. The multi-hazard fragility of CMBC and SCBC were numerically investigated through incremental dynamic analysis. Results show that when multi-hazard effects were considered, the fragility of SCBC and CMBC could be significantly increased as compared with that of individual hazard. In addition, compared with CMBC, SCBC could effectively reduce the damage probability under the combined seismic and impact loading, especially for the severe damage state and the collapse state. Moreover, SCBC could effectively prevent seismic collapse after high-speed impact due to effect of PT tendons and energy-dissipating rebars.