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Fundamental study of structural analysis and back analysis of pile-foundation system

桩基体系结构分析及反分析基础研究

基本信息

批准号：
11650488
负责人：
YAMAGUCHI Eiki
金额：
$ 2.3万
依托单位：
Kyushu Institute of Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2000
项目状态：
已结题

项目摘要

A pile is often modeled as a beam on nonlinear elastic foundation so as to include the effect of subgrade reaction. In design codes, several methods of determining the coefficients of subgrade reaction are available. However, the accuracy of the coefficients thus obtained is not so high. The existing methods may not be satisfactory when the performance-based design procedure is introduced.For the purpose of improving the accuracy, it is desirable to conduct the in-situ experiment of a pile. In recent years, therefore, it has been tried to evaluate the coefficients of subgrade reaction based on the results of in-situ experiments. However, since the relationship between the subgrade reaction and the deflection of a pile is nonlinear, it is quite difficult, if not impossible, to obtain the coefficients of subgrade reaction analytically from the experimental results. The coefficients are evaluated by trial and error in most cases.Against this background, the numerical procedure for computing the deflection of a loaded pile has been established first in the present study. In this procedure, the finite element method with two-node beam elements is applied and the iterative method based on the Newton-Rahpson technique in incorporated. Based on this numerical procedure, the back-analysis procedure to determine the coefficients of subgrade reaction is proposed. In this back-analysis, the coefficients are evaluated by minimizing the difference between experimental data and computed values. In the proposed back-analysis, the accuracy of the coefficients of subgrade reaction for the lower layer of the multi-layer foundation is very sensitive to the error involved in the experimental data. From the viewpoint of the bending rigidity of a pile and the way the experimental data are handled, the strategies of improving the accuracy of the back-analysis are discussed.

为了考虑地基反力的影响，在非线性弹性地基上，通常将桩建模为梁。在设计规范中，有几种确定路基反力系数的方法。然而，这样得到的系数的精度不是很高。当引入基于性能的设计过程时，现有的方法可能不能令人满意。为了提高精度，有必要进行桩身原位试验。因此，近年来人们尝试在现场试验结果的基础上对路基反力系数进行评价。然而，由于路基反力与桩挠度之间的关系是非线性的，从试验结果中解析得到路基反力系数是相当困难的，甚至是不可能的。在大多数情况下，系数是通过试错法求得的。在此背景下，本文首次建立了计算荷载桩挠度的数值程序。在此过程中，采用了双节点梁单元有限元法，并结合了基于牛顿-拉赫普森技术的迭代法。在此基础上，提出了确定路基反力系数的反分析方法。在这种反分析中，系数是通过最小化实验数据和计算值之间的差异来评估的。在本文提出的反分析中，多层基础下层路基反力系数的精度对实验数据误差非常敏感。从桩的抗弯刚度和试验数据处理的角度出发，讨论了提高反分析精度的策略。