地下综合管廊边界条件对地震动力响应影响数值分析

为研究综合管廊动力边界条件对地震动力响应的影响,以厦门地区的代表性土层为例,建立动力有限元数值模型,土体本构采用小应变硬化模型,分别设定固定边界、黏性边界和自由场3种人工边界条件,进行Rayleigh波和地震底部剪切波作用下的场地响应研究;并根据变形特征及拟绝对加速度反应谱(PSA)评价3种边界的有效性,提出综合管廊地震动力分析的优化动力边界组合方法。研究表明:在地震波(底部水平加速度时程)及Rayleigh波的作用下,由于考虑了黏性边界对外行波的吸收,但未考虑地震动的输入问题及边界外半无限介质的弹性恢复性能,边界会对模型内部土体的水平位移产生限制作用,使得场地内水平位移响应偏小,而采用自由场边界则基本不存在这种限制作用,表现出强烈的振荡;采用激励侧固定边界、远离激励侧黏性边界、其余侧自由场边界的优化组合动力边界,在Rayleigh波和底部加速度时程共同作用下,二者引起的动力响应交叉干扰较少,可按线性叠加处理;同时,黏性边界对地震波引起的动力响应有一定范围的吸收,自由场边界对Rayleigh波引起的动力响应也有一定范围的变形限制影响。研究成果可供地下综合管廊结构地震响应精细化数值模拟及抗震设计参考。

Numerical Analysis on Influence of Boundary Conditions on Seismic Dynamic Response of Underground Utility Tunnels

To explore the influence of a utility tunnel's dynamic boundary conditions on its seismic dynamic response,the authors targeted at the typical soil layer in Xiamen,China,and analyzed the site response under the effects of Rayleigh waves and shear waves through building a dynamic finite element (FE) numerical model,adopting the hardening soil model with small strain stiffness (HSS) as the constitutive model of soil,and constructing the three artificial boundary conditions,namely fixed boundary,viscous boundary,and free field.After evaluating the effectiveness of the three boundary conditions in terms of deformation characteristics and pseudo-spectral acceleration (PSA),the authors proposed an optimized dynamic boundary combination conditions in the seismic dynamic analysis of utility tunnels.The research results showed that under the effects of seismic waves (bottom horizontal acceleration time history) and Rayleigh waves,a viscous boundary condition only touched upon the absorption of external traveling waves while leaving out of the problem of seismic input and the elastic resilience of semi-infinite media outside the boundary,thus imposed restrictions on the soil mass's horizontal displacement within the model,and which resulted in a smaller horizontal displacement;under a free-field boundary condition,not the foregoing restrictions but the strong oscillations occurred;under the optimized dynamic boundary combination conditions of the excitation-applied side adopted fixed boundary,the excitation-free side viscous boundary,and the rest sides free-field boundary,there was less dynamic response cross interference under the effects of Rayleigh waves and bottom acceleration time history,so that the signals could be treated by linear superposition.In the meantime,the viscous boundary could absorb the dynamic response induced by seismic waves to a certain extent,and the free-field boundary could limit the deformation of the dynamic response induced by Rayleigh waves to some degree.The research findings are expected to provide a reference for an elaborate numerical simulation of the seismic response of underground utility tunnels and their seismic design.