考虑下卧弹性基岩的地下结构抗震分析模型

针对广泛采用的振动方法仅能考虑下卧刚性基岩条件的问题,基于等效节点荷载地震动输入方法和等位移边界,提出了可以考虑下卧弹性基岩恢复力和反射/透射地震波向地层深处逸散效应的地下结构抗震实用分析模型。介绍了等效节点荷载输入原理,通过数值算例验证了等位移边界的适用性。通过均质和成层场地算例,验证了分析模型正确性。以上海场地为例,对比分析振动方法与本文分析模型,地表位移和隧道结构内力响应初期相近,而后期差异显著,体现了下卧刚性基岩和弹性基岩不同场地条件的区别。下卧弹性基岩场地条件地下结构抗震分析,采用本文模型更符合实际情况。

A Seismic Analysis Model of Underground Structure with Elastic Base Condition

The widely used vibration analysis model can only consider the condition of the underlying rigid bedrock. On the basis of the equivalent node force method for seismic wave input and the repeatable boundary, a seismic analysis model of underground structure for the general one-dimensional SV wave propagating vertically upward problem was proposed in this paper. The model can take into account the effect of elastic base, namely both the restoring force of elastic base and the dissipation of seismic waves outward. The viscous-spring boundary and the corresponding equivalent node force formulation were introduced. The repeatable boundary was validated with a numerical example as well. With elastic homogeneous and layered ground cases, the accuracy of the analysis model was verified by providing comparisons between its results and analytical solutions. Taking Shanghai layered ground as an example, the comparison analysis between the vibration method only considering rigid base condition and the analysis model in this paper was conducted. Both free field response and the internal force response of tunnel structure from the analysis in this paper are consistent with those from vibration model at the beginning, but there are significant differences in the later stage because the difference between elastic base and rigid base. The analysis model in the paper is in line with the actual situation for seismic analysis of underground structures with elastic bases condition.