Influence of velocity pulse effect on earthquake-induced track irregularities of high-speed railway track–bridge system under near-fault ground motions

The near-fault ground motion records show a noticeable velocity pulse effect, which poses a significant seismic threat to the high-speed railway track–bridge system. This study conducts the seismic response analysis of the track–bridge system under near-fault ground motions with forward directivity and fling-step effects. It quantifies the degree of damage of each track–bridge system’s key component using the component's stiffness degradation coefficient. In addition, this research investigates the influence of velocity pulse effects from near-fault ground motions on earthquake-induced residual geometric irregularities and earthquake-induced dynamic irregularities. It explores the post-earthquake running performance of high-speed trains based on the input of earthquake-induced irregularities, providing a theoretical basis for the seismic design method of the track–bridge system based on running safety. The research results indicated that the stiffness degradation of the track–bridge system under near-fault pulse-type ground motions is more severe compared to near-fault non-pulse ground motions and mid-far-field ground motions. The amplitudes of earthquake-induced residual geometric irregularity and earthquake-induced dynamic irregularity of rails under near-fault pulse-type ground motions are much greater than those under near-fault non-pulse and mid-far-field ground motions. The earthquake-induced alignment irregularity significantly impacts high-speed trains' derailment coefficient and transverse acceleration. Consequently, failing to account for the velocity pulse effect of near-fault ground motions can lead to an overestimation of the post-earthquake running capacity of the track–bridge system. Seismic design considerations for high-speed railway bridges must prioritize the influence of velocity pulse-type ground motions.