Displacement Response Analysis of Regular Highway Girder Bridges Under Near-fault Pulse-type Ground Motions

In order to investigate the ductility demands and post-earthquake residual displacement of regular highway girder bridges under near-fault ground motions with velocity pulse, the bridges were simplified as nonlinear single degree of freedom (SDOF) systems, and a simple pulse model was used to simulate the near-fault ground motions with velocity pulses. Influences of amplitude and duration of velocity pulse, the natural period, as well as stiffness and strength degradation and pinching of the SDOF system on the ductility demand and residual displacement were systematically analyzed by dint of NSPECTRA software. The key parameters of near-fault ground motions with velocity pulse and the coupling effect of the natural period of the SDOF system were analyzed by range analyses and variance analyses of the orthogonal test design. The results show that the natural period and amplitude of velocity pulse are two main factors affecting the ductility demands and post-earthquake residual displacement of the SDOF systems, and the post-earthquake residual displacement of the SDOF systems generally increases with the increasing amplitude of velocity pulse. The duration of velocity pulse mainly affects the natural period at the peak point of the ductility demand spectrum, with less influence on the post-earthquake residual displacement. Both stiffness degradation and pinching will remarkably increase the ductility demand and post-earthquake residual displacement of the SDOF system in a short natural period, and have little influence on the SDOF system in a long natural period. The post-earthquake residual displacement increases with the development of stiffness degradation, strength degradation or pinching of the SDOF system. Besides, there is the coupling effect between the natural period of the SDOF system and the amplitude of velocity pulse, but the coupling effects of others are very small.