桥梁群桩基础非线性静力计算模型及拟静力试验研究

 线弹性地基反力法(m法)仅适用于正常使用时桥梁桩基础变位较小的情况，但在强震作用下基础的变位较大。为了研究桩基础在地基土及桩身进入非线性状态下的水平承载能力及变形特性，通过群桩基础缩尺比例模型，采用拟静力试验研究桩基础的破坏机制、承载能力、变形性能以及滞回特性。提出水平荷载作用下群桩基础的非线性静力计算模型，在该模型中采用分布PMM塑性铰模拟变轴力作用下桩身的弹塑性，采用美国API规范给出的p-y曲线、t-z曲线以及q-z曲线模拟地基土的非线性(其中，p为桩侧土水平抗力，y为水平位移，t为桩周土竖向摩阻力，q为桩端土竖向抗力，z为桩土竖向相对位移)。研究结果表明：(1) 本文提出的分析模型与模型试验结果吻合较好；(2) 可采用Clough退化双线性模型模拟桩基础的滞回特性；(3) 桩身受力薄弱部位在桩顶以下0～4倍桩径范围内。研究结果可为应用能力谱法评价桩基础的抗震性能提供参考。

NONLINEAR STATIC CALCULATION MODEL AND PSEUDO-STATIC TEST OF PILE GROUP BRIDGE FOUNDATIONS

Horizontal bearing characteristics of bridge pile foundations can be analyzed by using linear elastic subgrade reaction method(m-method) when displacement of pile foundation is generally smaller. However，displacement of pile foundations is often larger under the effect of strong earthquakes. In order to understand the horizontal bearing capacity and deformation characteristics of pile foundations considering nonlinear behaviors of pile shaft and subsoil，a model of pile foundations is constructed. Failure mechanism，bearing capacity，deformation characteristics and hysteresis characteristics of pile foundations are studied by using pseudo-static test. A nonlinear static calculation model of pile group foundations is put forward under horizontal load. The elastoplasticity of pile shafts in variable axial loads is simulated by distributed PMM plastic hinge；and nonlinearity of subsoil is simulated by the curves of p-y，t-z and q-z，respectively，which have been given in the code of American API；where p is horizontal soil resistance at lateral of pile shaft；y is horizontal displacement；t is vertical frictional resistance around piles shaft；q is vertical bearing resistance at pile tip；z is vertical relative displacement of interface between pile and soil. The results show that：(1) The numerical results are in good agreement with those obtained from experiments. (2) Hysteretic characteristics of pile foundations can be simulated using Clough degradation bilinear model. (3) Weak positions of pile shaft are 0–4 times around the radius of pile below pile top. The results can provide references for evaluating seismic performance of bridge pile foundation using capacity spectrum method.