考虑土体屈服的纵横荷载单桩变形内力分析

Analysis of deformation and internal force for single pile under combined vertical and lateral loads considering yielding of soil

为提高桩身变形较大时纵横荷载单桩的设计计算水平,假定地基反力系数沿深度线性增加,考虑土体屈服及纵向荷载的P-Δ效应并计入桩身自重和桩侧摩阻力的影响,得到了地面以下桩身变形和内力的幂级数解。结合已有的地面以上桩身响应的幂级数解,采用Fortran语言编制了计算程序。计算结果表明:桩顶位移、地面处桩身位移及桩身最大弯矩均随纵横向荷载和自由段桩长的增加而增大,并随土体屈服位移的增加而减小;纵向荷载足够大时桩基失稳;桩顶约束条件对桩的响应影响很大。计算值与模型试验的实测值吻合较好,所得解和程序是可靠的。

In order to improve the design and calculation of single piles under combined vertical and lateral loads when the pile deformation is comparatively great, considering the p-A effect （with the meaning of vertical load can magnify the deformation induced by lateral load） caused by vertical load and yield of soil, dead weight of the pile, and skin friction of the pile side, assuming that the coefficient of subgrade reaction increases linearly with depth, the power series solutions of the deformation and internal force for the pile shaft under ground surface are obtained. Combining the pre-existing power series solutions for the pile shaft above ground, the relevant computer program is developed by Fortran language. The calculation results indicate that the displacements at the pile head and the ground surface, and the maximum bending moment increase when the vertical and lateral loads, and the pile length above ground increase; and decrease when the yield displacement of soil increases. The vertical load may cause the instability problem for the pile. The boundary condition at the pile head plays an important role in pile responses. The computed and the model test results are in good agreement, meaning that the obtained solutions and program are dependable.