ABSTRACT
Near-fault ground motion is the motion that is typically assumed to be restricted to within 20 km of a fault (Mavroeidis & Papageorgiou 2003). However, this definition is not universal because near-fault effects attenuate as distance increases, which, in turn, leads to a greater effect of factors such as magnitudes and local site conditions on ground motion. The special characteristics of near-field ground motions are directly related to the earthquake source mechanism, rupture direction relative to the site, and slip direction of the rupture fault. The distinguishing characteristic of near-fault ground motion is the pulses generated by the directivity effect and fling-step effect. These pulse-type ground motions often contain one or more distinct pulses in the acceleration, velocity and displacement time histories, most frequently in velocity. Meanwhile, many new typical characteristics including hanging wall effect and vertical effect are also gradually recognized (Li &
1 INTRODUCTION
With rapid development and urbanization in China, exploitation and utilization of underground space has become a major concern. By the end of 2015, subways have been built or approved for construction in 37 Chinese cities with a total operating mileage 2933 km and 1947 operating subway station approximately. As a result, the structural styles of the subway underground structure become more and more complicated. In recent years, the strong earthquake disaster investigations indicate that underground structures suffered severe damage in near-fault area, such as the 1994 Northridge earthquake, 1995 Kobe earthquake, 1999 Kocaeli earthquake and 1999 Chi-Chi Earthquake (Samata et al. 1997, Kalkan et al. 2006, Corigliano 2007, Cunha et al. 2014). But the studies on the effect of near-fault ground motion on the seismic behavior of underground structures are limited (Chen et al. 2010, Tao et al. 2011, Corigliano et al. 2011, Davoodi et al. 2013, Zhao et al. 2015). Selected a set of near-fault ground motions of Loma Prieta and Coalinga records as seismic inputs, Chen et al. (2010) carried out the simulation analysis for the Double-layer vertical overlapping metro tunnels based on finite element software ABAQUS to investigate the seismic response of subway underground station. It was shown that the relative horizontal displacement induced by near-fault ground motion was greater than that induced by far-field ground motion in metro tunnels. At present, the subway station model with double-layer three-span
Xie 2007). The ground motions are characterized by pulse-type wave shape, long pulse period, abundant long-period components, and sometimes large permanent ground displacement.
