Abstract
Seismic analysis of tunnels close to or crossing seismogenic faults is a complex problem, which is often neglected at the design stage for the lack of specific codes or guidelines and also because underground structures are considered less vulnerable than that of the corresponding above-ground facilities. Near-fault ground motions are generally assumed to providing more powerful energy to tunnel structures. Therefore, a recently developed velocity pulse equivalent model is proposed to synthesize the artificial near-fault pulsed ground motion for the seismic response behavior of the tunnel structure. A newly proposed nonlinear dynamic time history methodology, the incremental dynamic analysis method, is introduced into the analysis of seismic performance and fragility for tunnel structures. This study takes the Zheduoshan tunnel as a case study to illustrate the effects of velocity pulse on the seismic response behavior and seismic performance. The applicability of different seismic intensity measures is preliminarily discussed, and the vulnerability of the tunnel structure at different characteristic locations is analyzed. Afterward, the seismic vulnerability probabilities of the tunnel structure under the action of the near-fault pulsed ground motions and the far-field ground motions are presented, and then, the failure probabilities of the tunnel structure under the three-level support requirements are obtained. Research results provide an objective assessment of the velocity pulse effects and acts as a reference for the likely seismic damage assessment of tunnel structures.
Highlights
It is a fact that underground structures are relatively less vulnerable than that of the corresponding above-ground facilities [1, 2]
Because of the focal mechanism and the attenuation characteristics of seismic waves, the most significant difference between nearfault ground motions and far-field ground motions is the velocity pulse waveform generated by the directional effect and the sliding effect. e velocity pulse has the characteristics of a simple waveform, strong action, and long period
The effects of velocity pulses on the seismic response and seismic performance of the tunnel structure are determined. e Incremental dynamic analysis (IDA) method is introduced to the research field of seismic performance on railway tunnel engineering. e following conclusions are drawn: (1) A recently developed velocity pulse equivalent model is proposed to synthesize the artificial nearfault pulsed ground motion, which is combined with the specific site attenuation characteristics of ground motions
Summary
It is a fact that underground structures are relatively less vulnerable than that of the corresponding above-ground facilities [1, 2]. Several pieces of literature show that tunnels and underground structures located in the seismically active regions suffered severe damages [6,7,8,9]. Is phenomenon has attracted widespread attention from scholars at home and abroad It is generally difficult for some important transportation tunnels or lifelines for water delivery to avoid crossing seismically active regions or even active faults [10, 11]. Erefore, a special study on the effect of near-fault ground motions on the tunnel structures is required. Because of the focal mechanism and the attenuation characteristics of seismic waves, the most significant difference between nearfault ground motions and far-field ground motions is the velocity pulse waveform generated by the directional effect and the sliding effect. Housner and Hudson [15] observed that near-fault ground motions are still very destructive even when the magnitude and PGA both are small. [16, 17] analyzed the stability of the underground caverns of Baihetan
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