纵向非一致激励下自由场土体的非线性地震反应研究

Nonlinear seismic response of free-field soil under longitudinal non-uniform seismic excitations

土体地震反应分析对结构的地震反应和抗震安全性评价具有重要的意义,以大型振动台模型试验为手段,研究一致激励和非一致激励下自由场土体的非线性地震反应规律及其影响因素,能够为结构的地震破坏机制分析提供支撑。通过对场地土体的动力特性、加速度响应、剪应力-剪应变曲线以及土体沉降的分析,研究了不同地震动、不同地震强度作用下自由场土体的地震动反应特性及其变化规律。研究结果表明:土体的非线性发展程度不仅与地震动记录有关,还与地震动输入方式、加载等级有关;在大震或纵向非一致激励作用下,土体运动的不一致性导致了更强的土体结构性变化,频率降低,阻尼比增大,土体刚度弱化,土体的非线性发展相对较快;土体剪应力-剪应变曲线和沉降曲线的变化规律一定程度上也反映了土体的塑性发展情况。所得结论和自由场地震反应宏观现象一致,彼此佐证了结论的合理性。

Soil seismic response analysis is of great meaning to the seismic response and seismic safety evaluation of structures. In this study, the non-linear seismic response law of soil in free field under uniform and non-uniform excitation and its influencing factors are studied by means of large-scale shaking table model test, which can provide support for analyzing the seismic failure mechanism of structures. By analyzing the dynamic characteristics of soil, acceleration peak magnification coefficient, shear stress-shear strain curve and soil settlement, the ground motion response characteristics and variation of free-field soil under different earthquake motions and different seismic intensities are studied. The results show that the non-linear development degree of soil is not only related to the record of ground motion, but also to the input mode and loading level of ground motion. In the case of large earthquake or longitudinal non-uniform excitation, inconsistent movement of free-field soil leads to stronger soil structural change, decrease of frequency, increase of damping ratio, weakening of soil stiffness and relatively faster nonlinear development of soil. The variation law of soil shear stress-shear strain curve and settlement curve also reflected the plasticity development of soil. The conclusions obtained are consistent with the observed macroscopic phenomena of the free-field seismic response, which mutually corroborated the rationality of the results.