动态施工条件下竖向立柱的承载力和稳定性研究

竖向立柱是基坑逆作法设计的关键环节之一，而动态施工下侧向约束则是决定立柱稳定承载力的主要因素。针对逆作施工中立柱的轴压稳定问题，采用有限元方法获得立柱轴压屈曲荷载，进而通过杆件欧拉公式反推获得立柱计算长度系数。采用线性特征值屈曲分析研究地基土分步开挖、侧向约束动态变化下竖向立柱的承载力和稳定性，提出了竖向立柱稳定承载力分析时计算长度系数的拟合公式。非线性屈曲分析考虑了几何大位移的影响，通过施加初始几何缺陷获得立柱屈曲后的平衡路径。结果表明，含初始缺陷的立柱实际承载力一般要比特征值屈曲荷载小，且初始缺陷幅值越大，立柱的稳定承载力越小。

Bearing capacity and stability of vertical column under dynamic construction

The vertical column is a key step of the design of foundation pit using top-down method; and the lateral restraint under dynamic construction is the main factor to determine the stability of the vertical column. For the axial compression stability of the vertical column under top-down construction, the finite element method is used to obtain the buckling load; and then through Euler formula of rods, the calculation length coefficient of the vertical column is obtained by inverse derivation. The linear eigenvalue buckling analysis is applied to study the capacity and stability of the vertical column under the dynamic variation of the excavation by steps of foundation soil and the lateral restraint. Then the fitting formula of the calculation length coefficient is put forward in the analysis of the stability bearing capacity for the vertical column. Nonlinear buckling analysis takes into account the influence of the geometric large displacement; and then the equilibrium path of post buckling is obtained by applying the initial geometric imperfection. It is shown that the actual bearing capacity of the vertical column with initial imperfection is smaller than that of the eigenvalue buckling load; and the lager the initial imperfection amplitude, the smaller the stable bearing capacity of the vertical column.