Nonlinear analysis of pile groups subjected to combined lateral and torsional loading

Abstract

An empirical approach has been developed to analyze the nonlinear response of a pile group with arbitrarily distributed piles subjected to combined lateral and torsional loading. In this approach, the concept of instantaneous twist center is applied to analyze the displacement relationship of pile heads and establish the static equilibrium equations of the pile cap. The horizontal interaction among the individual piles is considered through the generalized p-multiplier. The coupling effect of lateral resistance on the torsional resistance of each pile is quantified using an empirical factor β; the lateral and torsional nonlinear responses of individual piles are modeled by p-y and τ-θ curves, respectively. The proposed approach not only captures the most significant aspect of the group effect and coupling effect in a pile group subjected to combined lateral and torsional loading, but also automatically updates p-multipliers of individual piles based on pile cap displacements. The proposed approach was verified using results of model tests on pile groups subjected to lateral loading, torsional loading, and combined lateral and torsional loading, separately. In general, the pile cap response and the transfer of applied loads in the pile groups agree well with the test results.

概要

目 的

群桩基础在近海建/构筑物及桥梁中广泛应用, 而风、 浪、 船舶撞击等在群桩基础中产生的水平和扭转荷载往往影响群桩基础的安全. 本文旨在提出一套能够计算水平和扭转荷载联合作用下的群桩非线性响应简化分析方法.

创新点

1. 采用广义 p 乘子法考虑群桩中各桩水平变形导致的桩-土-桩相互作用; 2. 建立基于瞬时转动中心的基桩桩头位移关系和承台平衡方程.

方 法

1. 通过理论分析给出基桩桩头位移之间的关系, 建立承台平衡方程; 2. 采用荷载传递模型 (p-y 和 τ-θ 曲线) 模拟桩周土体非线性响应; 3. 采用广义 p 乘子法考虑群桩中各桩水平变形导致的桩 -土-桩相互作用, 并采用耦合因子计算基桩中推-扭耦合响应; 4. 通过迭代方法求解各基桩 p 乘子和群桩响应.

结 论

1. 多组算例均表明本文提出的群桩非线性分析模拟能够较准确地模拟群桩响应, 尤其在承台位移较大的情况下; 2. 广义 p 乘子能够有效地模拟群桩效应的主要部分; 3. 模型中的简化公式能够应用于实际工程问题分析.