用节点位移的主-从关系考虑扩底桩的端承面尺寸效应

Using nodal displacement master-slave constraint to consider the dimensional effect of head-enlarged pile

针对桩－土体系有限元数值分析模型中桩端尺寸效应的模拟问题进行了讨论。利用桩端节点位移的主－从关系建立了桩端－土体界面节点位移的约束条件。如果在有限元数值分析中将柱体模拟成梁杆单元集合体并在桩端施加这个约束条件，则可考虑桩端尺寸效应，特别是扩底桩桩端尺寸效应。为了显示桩端尺寸效应的影响进行了数值对比研究。数值结果表明：随着桩端尺寸的增大，桩端土体的塑性区分布及发展有很大的不同，桩的Ｐ－ｓ沉降曲线的差异很大，因此该效应对用数值法计算扩底桩的承载力是不容忽视的。

The paper has profoundly discussed numerical modelling of the pile structure in soil which is mainly subjected to the axial vertical load, and on the basis of the nodal dislacement constrained features, a kind of nodal displacement principle-subordinate constraint condition was proposed in order to incorporate the dimensional effect of the pile head into the pile - soil integrity numerical model without need of developing new kind of finite element model. Finally the contrast numerical study of the dimensional effect of the head-enlarged pile structure on the pile - soil integrity numerical model was carried out, the numerical results indicate that the larger dimension of the pile head the greater effect it will exert on the plastic strain distribution and its developing manner in soil near the pile head, which hence greatly differentiates the head-enlarged pile supporting capacity and should be taken into account seriously in its calculation.