高层建筑地基基础概念设计的思考

基于高层建筑箱、筏、桩筏基础变形、反力等实测资料的分析指出,按传统理念设计的箱基、筏基、桩筏基础有两个缺陷:一是呈现明显的碟形沉降引起上部结构的较大次应力;二是基底马鞍形反力分布导致基础板或承台冲剪力和弯矩显著增大。为使差异沉降和箱、筏承台的内力减至最小并改善上部结构受力性状,提出变刚度调平概念设计。对于框筒、框剪结构,应强化核心筒区的桩土刚度(调整桩长、桩径或桩数),相对弱化外围刚度;对于主裙连体建筑,应强化主体,弱化裙房(采用天然地基、复合地基和疏短桩基);对于箱、筏基础,可局部强化核心筒区(采用桩基或刚性桩复合地基)。对于上述变刚度调平概念设计,进行上部结构—基础—桩—土共同作用分析,进一步优化布桩和承台配筋。通过大比例现场模型试验对上述优化设计理念进行了验证,并应用于10余项工程,取得了良好的技术经济效果。

Review and optimization of the conceptual design of foundations for high-rise buildings

Analyses of measured data of high-rise building foundations indicate that there are two shortcomings for those box,raft,pile-raft foundations designed by using the traditional design concept.One is the obvious disk-shape settlement distribution,which may result in significant secondary forces in the superstructure,and the other is the saddle-shape reaction distribution,which may result in increased punch force and moment in foundation slabs.In order to minimize the differential settlement,thus to improve the foundation and structural performance,an optimal conceptual design is proposed,based on foundation rigidity adjustment.For frame-tube and frame-shear wall structures,the core area pile-soil rigidity(by adjusting pile length,diameter or numbers)should be enhanced whereas relatively weaker external area pile-soil rigidity may be adopted.For tower-podium connected buildings,a weaker podium area foundation rigidity(applying nature subsoil,composite foundation or widely spaced short piles)should be employed.For box or raft foundations,one might partially strengthen the core area(piling or ground treatment).Base on conceptual designs,analysis of the interaction of superstructure-foundation-pile-soil helps to further optimize pile arrangement and reinforcements in the slab.The optimal design concept has been verified through in-situ large scale model tests and has been applied to more than ten projects with good results under both the technical and economical considerations.