序列型地震作用下地铁车站损伤分析

Seismic damage assessment of subway station subjected to mainshock-aftershock sequences

以往地下结构抗震分析中,通常只关注单次地震作用下结构峰值响应,对地下结构在序列型地震动下损伤机理认识不足。聚焦序列型地震动下地铁车站的损伤分析,以揭示余震对地下结构损伤的影响规律并探究合理的结构抗震性能指标。挑选7条真实主余震序列,通过地震动反演生成下卧基岩序列地震记录。考虑序列地震动方向性和相对强度的影响,开展土-地下结构系统非线性动力时程分析,并采用峰值层间位移角,残余层间位移角和Park-Ang指数评估地下结构地震损伤。分析结果表明,余震的方向性对损伤的影响呈现不规律性。主余震相对强度较大时,余震引起主震震损后的地下结构向更高级损伤状态跃迁。在地下结构地震损伤评价指标选择方面,残余层间位移角受主余震的相对方向影响显著,而峰值层间位移角无法反映余震强度小于主震时对结构造成的损伤,均不适合作为表征余震造成地下结构附加损伤的指标。而Park-Ang指数除能反映过度变形损伤外还能反映累积滞回能量耗散,能较好地表征结构在主余震下的真实损伤,较适合作为序列型地震作用下地下结构损伤评价指标。

In the previous seismic analyses of underground structures,only the peak structural response under the main earthquake is considered,but the damage mechanism of underground structures subjected to sequential ground motions has not been fully understood yet.Special attention is paid to the seismic damage analyses of subway station structures under sequential ground motions.The seismic damage evolution of underground structures under aftershocks and the feasible seismic performance indices are explored.Seven bedrock earthquake records,which are back-calculated from seven mainshockaftershock sequences,are adopted.Considering the influences of the directivity and relative intensities of sequential ground motions,nonlinear dynamic time history analyses of soil-underground structure system are performed.The peak inter-story drift ratios,residual inter-story drift ratios and Park-Ang index are used to evaluate the earthquake damage of the subway station.The results show that the directivity of aftershocks has irregular influences on the structural damage.When the relative intensity between the mainshock and aftershock is large,the underground structures damaged during the mainshock are likely to transit to a severer damage state.In terms of the selection of seismic damage evaluation indexes for the underground structures,the residual inter-story drift ratios are significantly affected by the relative direction between the mianshock and the aftershock.While the peak inter-story drift ratios cannot reflect the damage to the structures caused by the aftershock intensity smaller than the main shock.Therefore,both the peak and the residual inter-story drift ratios are not suitable for representing the additional damage of the underground structures caused by the aftershock.The Park-Ang index can reflect the excessive deformation damage and the accumulated hysteretic energy dissipation,which can better illustrate the actual damage of the structures under the mainshock-aftershock sequences,and is more feasible as the damage evaluation index of the underground structures subjected to sequential earthquakes.