Empirical study on reduction in input motions to improve the seismic performance based design of buildings

本文研究了强地震动作用下土-结构的非线性相互作用效应，为抗震设计提供参考。首先，利用国内外近年来的典型大震地震动记录，通过地震反应分析，研究了土-结构相互作用对建筑物减震的有效性。在分析中，使用简单的摇摆-摇摆模型，并考虑了建筑物的非线性。假定建筑物支承在弹性均匀软土上的直接基础上。分析表明，土-结构相互作用的减震效果与地震动特性、建筑层数和抗震性能密切相关。其次，通过干砂土中桩基的循环荷载试验，研究了大桩头位移区群桩效应的非线性。试验参数为桩数、加载速率、土的相对密度和群桩线形。测试所得的主要结果概述如下：桩周土体在小振幅下也会发生明显的变形; 2）桩顶剪切力-位移关系、桩顶割线刚度和等效阻尼系数在很小的位移范围内也表现出明显的非线性; 3）桩顶剪切力在土体破坏后基本保持不变，4）群桩效率随桩顶位移的增加变化不大; 5）桩顶剪力占水平荷载的比例受桩的屈服、土体的破坏以及桩数、桩位、土体密度、荷载方向等因素的影响。

Nonlinear soil-structure interaction effects under strong ground motions are studied to consider in the seismic design.First, effectiveness of soil-structure interaction in earthquake response reduction of buildings is studied by earthquake response analyses using representative ground motion record of recent domestic or foreign big earthquakes. In the analyses, simple sway-rocking models are used and non-linearity of buildings is considered. It is assumed that buildings are supported by direct foundation on the elastic uniform soft soil. From the analyses, it is pointed out that the damage reduction effects by soil-structure interaction greatly depend on the ground motion characteristics, number of stories and seismic performance of buildings.Next, cyclic loading tests for pile foundation in dry sand are conducted to investigate the nonlinearity in the pile group effects in large pile-head-displacement region. The experimental parameters are the number of piles, loading rate, relative density of soil and alignment of pile group. The major findings obtained from tests are summarized as follows: 1) the soil around piles deformed significantly even at small amplitude, 2) shear force-displacement relationship, resultantly secant stiffness and equivalent damping factor, at pile head shows significant nonlinearity even in very small displacement range, 3) shear force at pile head hold almost constant value after the soil get failed, 4) variation in pile group efficiency with increase in pile-head displacement is not so large, 5) the ratio of the shear force at pile head to the total horizontal load is affected by the yield of piles and the failure of the soil as well as the number of piles, pile location, soil density, and loading direction.