【作者】 王会杰；

【导师】 郭院成；

【作者基本信息】 郑州大学 ， 结构工程， 2010， 硕士

【摘要】 近年来,复合地基基于变形控制设计原则的理念越来越被土木工程界人士重视。复合地基的变形控制研究中,基础的沉降变形是关键点,沉降变形计算中应充分考虑各种因素对基础沉降的影响。本文总结了影响基础筏板沉降的各种因素,重点研究了支护结构的存在对筏板沉降的影响规律。并基于减小筏板沉降差的原则,研究了复合地基变刚度概念设计的方法。本文采用数值模拟方法,把单桩的现场载荷试验结果Q-S曲线应用到筏板的沉降分析中,同时考虑支护结构及基础埋深的影响,建立复合地基基础的三维有限元模型。在上部结构采用框剪结构而使筏板表面荷载分布呈中心大边缘小的情况下,对等间距长短桩、同一桩距中心长桩边缘短桩、同一桩型中心桩距小边缘桩距大、基于等刚度布桩时抽桩等各种复合地基变刚度方案进行沉降分析。本文得出的主要结论如下：(1)支护结构的存在对筏板下有增强体的复合地基影响不明显,但是对筏板下是天然地基的筏板沉降有显著影响。(2)采用增加桩长的方法可以减少筏板的沉降。但是在等刚度布桩时采用增加桩长的方法解决不了筏板差异沉降大的问题。(3)在上部结构采用框剪结构而使筏板表面荷载分布呈中心大边缘小的情况下,为了减少筏板的差异沉降,根据中心区域支承刚度大,边缘区域支承刚度小的原则布桩时,筏板下支承刚度大的范围要稍大于上部核心区荷载分布范围。基于本文的计算分析,采用中心长桩边缘短桩且中心长桩布置面积占核心筒荷载分布面积的130%左右的变刚度方案为最佳方案,此时桩体荷载分担均匀,沉降曲线平缓。但是这一范围是与支承刚度的相对比值有关的。(4)减少筏板边缘部分的支承刚度,筏板边缘的沉降值增加,中心部位的沉降值变化很小,以使筏板的沉降曲线变缓,差异沉降减少,筏板下桩体荷载分担更趋均匀。但是筏板边缘的支承刚度削弱太严重,会使筏板的沉降曲线呈中心小、两边大的上凸状,达不到沉降控制的效果。(5)减少筏板差异沉降的关键在于选择合适的筏板中心区域的支承刚度与边缘区域的支承刚度比值及刚度布置范围。更多还原

【Abstract】 In recent years, the concept of design methods of composite foundation based on the controlling settlement principle attracts more and more attention of the civil engineering professions. With regard to the research about composite foundation according to the controlling settlement, foundation’s settlement is a critical point. And the design methods of composite foundation according to the controlling settlement should consider various factors sufficiently. This paper summarizes various factors on the settlement of the raft foundation, and focus on the impact of the supporting structure. Based on the principle of reducing the raft foundation differential settlement, this paper also studies the conceptual design method of variable stiffness composite foundation.The Q-S curve will be used to calculate the settlement of composite foundation. Using the numerical simulation method and considering of the supporting structure and the depth of foundation, a three-dimensional finite element model of composite foundation is established. The loads distribution of frame-shearwall structure is large in the center and small on the edge of raft. Under the circumstances, this paper analyses the settlement of variable rigidity composite foundation with long-short-pile of the same pile spacing, with long piles in the center and short piles on the edge of raft, with a small pile spacing in the center and a large pile spacing on the edge of raft, with reducing the equal rigidity composite foundation edge piles. The main conclusions are as followed:(1) The presence of supporting structure affects the settlement of raft. However, the influence on the foundation that has reinforced body(piles) is not distinct. But the presence of supporting structure affects the settlement of natural foundation significantly.(2) To increase the length of pile can reduce the settlement of the raft. But that can not solve the problem of differential settlement of raft in the equal rigidity (3) The loads distribution of frame-shearwall structure is large in the center and small on the edge of raft. Under the circumstances, to reduce the differential settlement, and basing on the principle that high bearing stiffness in the center regional and low bearing stiffness on the edge regional, the area of high bearing stiffness must be larger than the core area of upper structure. According to the analysis, the variable rigidity composite foundation with long piles in the center and short piles on the edge of raft is the best method. And the settlement control is very good when center area of long piles occupies about 130% of the core-tube load distribution area. In this case, different positions of the pile share load evenly. But this range is concerned with the ratio of the bearing stiffness.(4) The purpose of reducing the bearing stiffness on the edge of raft is mainly to increase the settlement on the edge of raft, while the settlement in the central part varies slightly, so that the settlement curve is smooth and the differential settlement decreases markedly. However, if the bearing stiffness on the edge regional is reduced severely, the settlement value will be very small in the center but large on the edge of raft. That fails to control the settlement.(5) The key point of reducing the differential settlement is to choose the right ratio of the center and the edge regional bearing stiffness and the corresponding arrangement region of bearing stiffness.更多还原