SV波垂直入射下成层半空间地震动输入模型比较

Comparison of seismic input models for a layered half plane subjected to vertically incident SV waves

在土-结构动力相互作用问题中常将该耦合结构体系分为远场和近场。远场地震动可施加在近场的底部和侧边界,或者仅施加在近场成层介质的底部。为研究这2种地震动输入模型的异同,文中利用比例边界有限元法严谨地模拟了远场动力刚度,实现等效地震动的输入;同时结合平面波波动理论,分析计算了SV波垂直输入时二维自由场地地震响应,研究了侧边界处地震荷载对自由场运动的影响,比较了不同地震动输入模型下等效地震力的大小。研究表明:侧向地震力对自由场动力反应的影响不可忽略,其影响随着近场宽度的增大而呈指数减少趋势。当均质弹性近场的宽深比(2 d/h)大于36时,采用底部输入模型求得的自由场运动数值解与理论解的误差在5%之内。在底部输入模型中,相比于考虑地震波在整个自由场传播,假设地震波在下卧层传播可减小自由场运动求解误差。

A soil-structure coupling system is often divided into a near field that is of interest and the remaining far field. Far-field excitations caused by earthquakes are applied at the bottom and lateral of the near field,or alternatively applied purely at the bottom in a case of layered half plane. The relation between these two approaches,however,is not clear and still needs future investigation. To this end,both the dynamic stiffness of the far field and seismic loading are modeled in a rigorous manner by using the scaled boundary finite element method. Then,numerical simulations on wave propagation in layered half planes subjected to vertically incident SV waves are performed using two seismic input models. In comparison with theoretical solutions,it is found that the influence of lateral-boundary seismic excitation on free field motion is reduced exponentially with the width of near field. The numerical results corresponding to pure bottom-boundary seismic loading are close to theoretical results with relative difference less than 5%,if the width-depth(2d/h)of the near field is greater than 36. When seismic load is applied on the bottom,the resulting free-field motion is more accurate by assuming wave propagation in an underlying half plane than in the whole field.