上部结构－桩基—地基共同作用数值分析及桩基变刚度调平优化设计

本文采用有限元法对高层建筑上部结构—桩筏基础—地基共同作用及相互影响进行了研究。研究表明:高层建筑上部结构—桩筏基础—地基共同作用及相互影响时，基础总体沉降和差异沉降随楼层的增加呈非线性变化趋势，上部结构中存在次应力，弯矩和轴力比常规法设计偏大；随楼层的增加，桩体对荷载的分担比在减少，土体分担比在增加；随着上部结构刚度的增加，荷载向角桩、边桩集中；增加筏板厚度，能减少一定的差异沉降和基础平均沉降，从而减少上部结构的次应力，提高地基土的荷载分担比，同时筏板下桩顶反力分布更不均匀，因此需要从筏板受力，以及考虑筏下桩、土的受力来综合确定一个合理的筏板厚度，使设计安全经济；随着地基土变形模量的提高，地基土分担的上部荷载增加，桩顶反力趋向平均，筏板最大弯矩逐渐减小。桩筏基础在均匀布桩条件下呈中间大边缘小的“碟型”分布。差异沉降是由于上部结构次生应力和筏板内力产生的。通过对地基土刚度以及桩长、桩径、桩距等五种桩基刚度的调整，并分析不同刚度对基础差异沉降影响可知:改变桩长的布桩形式并结合地基土刚度调整的中心布桩形式是高层建筑桩筏基础最佳设计方案。

Numerical analysis of interaction of superstructure-piled raft foundation-the foundation soil and optimal design for variable stiffness of the pile raft foundation

In this paper, finite element method was used to study the interaction and common effect among superstructure-piled raft foundation foundation interaction. The research results show that when the interaction of superstructure-the pile raft foundation-foundation and the influence among them occur, the foundation settlement of overall and differential subsidence with the increase of the floor change nonlinearly, the upper structure existing in secondary stress and the bending moment and axial force are larger than those with the conventional design method. With the increase of the floor, the pile body load sharing ratio reduces and the soil sharing ratio increases along with the increase of the upper structure stiffness and the load concentration on the corner pile and side pile. Increasing raft thickness can reduce certain differential subsidence and the average base settlement, thus reducing the secondary stress of the upper structure and improving of the load sharing ratio of foundation soil. At the same time the under raft reaction distribution on top of pile is more uneven, so it is needed to force from the raft and consider raft under the stress of the piles and soils forces comprehensive to determine a reasonable thickness of the raft, which makes the design safety and economy. With the increase of foundation soil deformation modulus, the upper load-sharing by the foundation soil increases, the top of the pile reaction tends to be average, and the maximum bending moment of the raft gradually decreases. Piled raft foundation under the conditions of uniform cloth pile was at the middle edge of the small "dish type" distribution. Differential settlement is due to the upper structure of the secondary stress and raft internal force. Through adjustment of five pile foundation stiffness of foundation soil and pile length, pile diameter, pile spacing, etc, the influence of different foundation stiffness to differential subsidence can be learned. Change in pile lengths of pile form of cloth and combination with the center cloth pile of the foundation soil stiffness adjustment in the form are the optimal design for high-rise building pile raft foundation.