基于高性能有限单元的单桩稳定性分析法

Stability analysis of single pile base on efficient finite-element method

现行的桩基设计方法主要基于线弹性理论及采用半经验假定,难以准确地检验长桩在土体非线性条件下的稳定性。基于非线性有限单元分析理论,提出了高性能桩单元分析法用于非线性分析,可直接检验单桩稳定性且无需假定桩的计算长度系数。在桩单元推导过程中,通过整合在单元内部的连续弹簧以考虑土-结构相互作用(SSI),能够大幅提升计算效率。使用牛顿-拉夫逊迭代法进行迭代运算,利用推导的相应单元切线刚度矩阵预测位移,并通过割线关系减少每一步迭代中产生的误差,在桩的大变形条件下采用更新拉格朗日法确定平衡条件。算例验证表明,桩单元模型在考虑土体非线性条件下,能高效、可靠地对单桩进行分析和设计。

Currently,the semi-empirical design method based on the linear elastic analysis assumption is commonly employed,which is incapable of examining the stability of the long pile embedded in complex ground mediums accurately.To this,this research adopts the nonlinear finite element method to establish an efficient pile element model for nonlinear analysis of piles.This approach can be utilized in nonlinear buckling stability analysis without assuming effective length factors.This paper elaborates the basic theory of the pile element.It’s worth noting that,the continuous springs along the element are integrated into the pile element formulations for considering the soil structure interaction(SSI)responses,which can significantly improve the computing efficiency.The element tangent stiffness matrixes are accordingly formulated for predicting displacement,and the secant relations are developed for eliminating accumulative errors in a Newton-Raphson incremental-iterative numerical procedure.The Updated-Lagrangian(UL)approach is developed for simulating large deflections of piles.Finally,several benchmark examples are provided for verifying the accuracy and efficiency of the proposed pile element model in analysis and design of piles with nonlinear surrounding soil.