冻土-结构相互作用体系地震响应机理及数值模型研究

Frozen soil is widely distributed in China. Freezing of subsoil can result in layering of a homogeneous site. It can also change the dynamic characteristics and predominant period of the site, producing a risk of seismic stability and safety of the superstructures. However, the current Chinese seismic design code of GB050011-2010Code for Seismic Design of Buildings classifies the site types and conducts seismic design based on normal soil, without considering the effect of frozen soil layers on the seismic response and the response spectra of the structures. This study takes the frozen soil-structure interact system as the research object, and conducts small-scale shaking table tests and numerical analysis: 1) to clarify the seismic characteristics of frozen soil with different freezing depth and site types, 2) to examine the influence rules on frozen soil-structure interaction system by the lifting off that may occur between foundation and soil and the nonlinear behavior as slipping, and 3) to establish a dynamic-coupling nonlinear model of the frozen soil-structure system on consideration of the separating effect between poles and soil and the inertial interactions of superstructures. The results of this study can provide useful references for analyzing the seismic performance of buildings in cold regions, and propose preliminary suggestions on seismic design at frozen sites for current codes.

我国冻土分布广泛，冻土层的存在使均质场地变为双层或多层地基，改变了地基土的动力特性和卓越周期，从而直接影响着上部建筑结构抗震性能的稳定与安全。而我国现行的《抗震设计规范（GB050011-2010）》对场地的分类和抗震设计按照常规土进行，没有考虑冻土层对结构地震动响应和反应谱的影响。本项目以冻土-结构相互作用体系为研究对象，通过小型振动台试验和数值分析相结合，研究地震作用下，不同冻结深度、不同场地的冻土特性以及基础与土体之间可能会发生的提离、滑移非线性因素对冻土-结构相互作用体系的影响规律。建立考虑桩-土分离效应及上部结构惯性相互作用的冻土-建筑结构动力耦合非线性计算模型。所得结论可为寒区建筑结构的抗震性能分析提供参考，从而对现行规范中冻土场地抗震设计提出初步建议。

为了揭示冻土环境中考虑冻土-建筑结构相互作用体系的动力特性，完善冻土-桩动力相互作用体系的地震响应规律、评估其安全性能，本项目在现有冻土力学试验方法和弹塑性本构理论的基础上，通过重塑冻结砂土的三轴试验，研究了不同围压、不同含水率、不同温度下冻土强度以及弹性模量等物理参数的变化规律。并基于冻土–结构动力相互作用体系的振动台试验，利用自行研制的室内冻土冻结系统，再现了地震激励下，冻土场地中上部结构和地基的震害现象以及砂质粉土的液化现象。研究了地震作用下不同冻结深度的冻土场地的地震响应及其对上部结构的地震响应的影响规律。另外，利用非线性有限元软件建立了考虑冻土对温度的依存性及地基液化引起的等效剪切刚度变化的非线性计算模型，所得结论可为寒区建筑结构的抗震性能分析提供参考，对促进冻土地区建筑结构的抗震设计理论的发展具有重要的意义。