Proposal for Modeling Nonlinear Sloil-Structure Interaction System Considering Amplification Effect of Surface Layers

在1995年兵古县南部地震期间，我们观察到在一个扩展区域内明显集中的破坏，作为所谓的破坏带的一种形式，其宽度与长度相比非常窄。造成这种破坏的原因之一是深层地下结构的复杂性，包括地震断层。另一个原因是表层的影响。本文讨论了表面层的放大效应、表面层复合刚度的评价以及土层与结构的相互作用效应。在此基础上，提出了以1995年兵库县南部地震为例的建筑结构遭受破坏性或灾难性地震运动时，考虑表层效应和土-结构相互作用的地震反应分析方法。考虑周围非线性土体介质，采用动力地基柔度（DGC）和土嵌基础或桩基础的阻抗来评价表层的复杂刚度。然后用DGC的有理函数表示表层的复合刚度，并用频率相关的弹簧-阻尼器系统代替。结果如下：(1)表层的放大效应很大程度上取决于表层的条件（深度、刚度等）。(2)简单的表层很容易被简单的弹簧-减震器系统所取代，而深层表层则变成了更复杂的弹簧-减震器系统。(3)建筑结构的地震反应分析必须考虑土-结构的相互作用，因为表层往往对建筑的地震反应有不良影响。(4)采用有理函数作为表层复刚度，可以简化土-结构相互作用体系的非线性地震反应分析。

During 1995 Hyogo-ken Nanbu Earthquake we have observed conspicuous concentration of damage in an extended area as a form of the so-called damage belt whose width was very narrow compared to its length. One of causes for this damage is the complexity of the deep underground structures including the earthquake fault. Another cause is the effects of surface layers.In this study, we discussed about the amplification effect of surface layers, the evaluation of complex stiffness of surface layers and the interaction effect between soil layer and structure. Then we proposed the earthquake response analysis method considering these effects of surface layers and the soil-structure interaction when building structures are subjected to ruinous or disastrous earthquake motion like 1995 Hyogo-ken Nanbu Earthquake.The complex stiffness of surface layers is evaluated by dynamical ground compliance (DGC) and impedance of soil-embedded base or pile foundation considering surrounding nonlinear soil media. Then the complex stiffness of surface layers is expressed by using the rational function of DGC and replaced with frequency-dependent spring-dashpot system.Results are as follows ; (1) The amplification effect of surface layers strongly depends on the conditions (depth, stiffness etc.) of the surface layers. (2) Simple surface layers can easily be replaced with simple spring-dashpot system, but deep surface layers becomes to more complex spring-dashpot system. (3) We must analyze earthquake response of building structure considering the interaction effect of soil-structure, because surface layers often have bad effects on earthquake response of building. (4) Nonlinear earthquake response analysis of soil-structure interaction system becomes easier by using rational function as the complex stiffness of surface layers.