水平循环及偏心荷载作用下群桩性状模型试验研究

发布时间：2018-01-06 20:34

本文关键词：水平循环及偏心荷载作用下群桩性状模型试验研究　出处：《浙江大学》2014年博士论文　论文类型：学位论文

【摘要】：近海工程项目通常体型巨大、结构高耸,其下部基础除了要承担上部结构的自重荷载外,还长期受到风、波浪、水流等水平循环荷载的作用。群桩基础在该循环荷载作用下不仅容易产生累积变形,极端条件下甚至可能发生破坏。另一方面,大型结构在承受水平荷载时,由于荷载作用方向的随机性,传递至下部群桩基础的荷载在某些情况下还可能存在一定的偏心距。这意味着基础将同时承受水平和扭转荷载的作用,从而产生复杂的受力和变形响应。目前人们对群桩基础在水平循环及偏心荷载作用下承载性状的认识存在很多的不足,因此有必要结合近海工程的特点对上述问题展开系统深入的研究。本文通过1g大比尺模型试验以及离心机模型试验,分别研究了高承台群桩在水平循环及偏心荷载作用下的受荷性状。本文开展的主要工作及相应的研究成果如下： (1)采用钢管及混凝土分别设计并制作了大比尺的单桩及群桩模型,利用浙江大学大型土工物理模型试验系统开展了一系列加载试验,对水平循环及偏心等复杂荷载条件下的群桩受力和变形性状进行了系统的研究。全部模型试验包括：1×2钢管群桩水平偏心加载试验、2×2混凝土群桩水平偏心加载破坏试验、3×3钢管群桩水平循环加载试验,以及相关的单桩加载试验。 (2)基于3×3钢管群桩水平循环加载试验,分析讨论了群桩水平刚度、基桩内力及荷载分配等响应随荷载循环的变化规律,并引入了循环效应系数以评估循环荷载对桩基水平承载性状的影响。研究结果表明,桩基的水平刚度随荷载循环次数的增加而减小,且先期循环加载历史会影响桩基后期的水平加载刚度；各级循环加载中,单桩及群桩的桩头峰值荷载随循环次数增加依次表现出稳定型、发展型和破坏型等三种不同的衰减形态,反映了桩周土体由弹性到塑性再到破坏的发展过程；群桩中各排基桩分担的荷载比例随着循环次数增加不断变化,其中前排桩分担的荷载逐渐增大；由于承台的约束作用,基桩轴向循环拉压受荷,导致群桩伴随水平循环加载过程产生严重沉降；荷载循环效应对群桩水平受荷性状的影响要比单桩大得多。 (3)基于1×2钢管群桩水平偏心加载试验,分析了群桩的整体变形以及基桩内力等响应,并通过ABAQUS有限元模拟,讨论了不同偏心距大小及基桩布置形式对群桩水平偏心受荷性状的影响。试验结果表明,水平偏心荷载下群桩中各基桩的内力存在较大的区别,离加载点近的基桩承担的荷载更大；受水平与扭转荷载耦合效应影响,群桩中基桩的抗扭承载力较单桩显著提高；基桩桩头扭矩及水平剪力共同抵抗水平荷载偏心引起的附加扭矩,且基桩剪力对抵抗群桩扭转的贡献随荷载的增加不断增大。数值计算结果显示,水平荷载偏心距对群桩整体变形的影响相对较小,但对基桩的内力影响较大；基桩布置形式显著影响群桩的水平和抗倾覆刚度,但对群桩的整体扭转响应影响较小。 (4)基于2×2混凝土群桩水平偏心加载破坏试验,揭示了群桩的渐进破坏过程,配合数值分析研究了各基桩的内力随加载的变化规律,并对混凝土群桩在水平偏心荷载下的破坏过程及机理进行了总结。研究结果表明,较高的加载高度、上部结构的自重以及桩身混凝土的开裂等因素加剧了群桩在水平偏心荷载下的倾覆破坏；群桩在加载初始阶段基本处于弹性状态,各基桩的水平刚度较大；当荷载超过一定的临界值后混凝土基桩先后出现开裂,群桩刚度随之降低,变形相应增大；上部结构自重荷载引发的P-△效应使前排基桩承受的轴向荷载迅速增加,最终前排角桩出现轴向偏压破坏,群桩及其上部结构随之发生整体倾覆。 (5)利用浙江大学ZJU-400土工离心机,开展了砂土中群桩承受水平及偏心荷载的系列模型试验,着重对比研究了直桩群桩与斜桩群桩在不同荷载条件下的变形及承载特性。试验结果表明,斜桩群桩的水平及扭转承载力均显著大于直桩群桩；水平偏心荷载下斜桩群桩中各基桩的桩顶位移差异较直桩群桩更大；斜桩群桩通过基桩轴向受荷可以更有效地抵抗水平荷载。数值计算结果表明,基桩斜度对群桩水平承载性状的影响较大,群桩水平刚度随基桩斜度的增加而增大。 (6)提出了考虑多向荷载共同作用的群桩分析模型；在刚性承台的假设下推导了群桩整体刚度矩阵的表达式；同时考虑不同方向的群桩效应以及基桩各向荷载之间的耦合效应影响,讨论归纳了基桩各向刚度的计算确定方法；总结了多向荷载共同作用下群桩分析的一般流程,并给出了相应的分析实例。
[Abstract]:Offshore engineering projects are usually large, high-rise structures, the lower base in addition to bear load of upper structure, has long been the wind, wave, flow and horizontal cyclic loading. In the pile foundation under cyclic loading is not only easy to deformation, damage may occur even under extreme conditions. On the other hand large, the structure under horizontal loads, due to the randomness of the loading direction, the load transfer to the lower part of the pile group foundation may also exist certain eccentricity in certain circumstances. This means that the foundation will also bear the horizontal and torsional loads, resulting in stress and deformation response of the complex. At present people understanding of pile foundation bearing capacity under horizontal cyclic and eccentric loads has many deficiencies, so it is necessary to combine the characteristics of the offshore engineering system An entry study.
Based on the 1g large scale model test and centrifuge model test, the load characteristics of high cap pile group under horizontal cyclic loading and eccentric load are studied respectively. The main works and corresponding research results in this paper are as follows:
(1) the steel and concrete were designed and manufactured a large scale single pile and pile group model, using Zhejiang University large soil physical model experiment system to carry out a series of loading tests on the level of circular and eccentric complex loading conditions of pile force and deformation properties were studied systematically. Including all model test: 1 x 2 level steel pipe piles eccentric loading test, 2 * 2 concrete pile group horizontal eccentric loading, 3 * 3 steel pipe pile group horizontal cyclic loading test, and the single pile loading test.
(2) based on the 3 * 3 steel pipe pile group horizontal cyclic loading test, discussed the pile stiffness, pile internal force and load distribution of the response changes with the load cycle, and the cycle effect coefficient to evaluate cyclic load bearing properties influence on the pile. The results show that the level of pile stiffness the degree of decrease with the increasing of the number of loading cycles, and cyclic horizontal loading loading history will affect the later pile stiffness; various cyclic loading, single pile and pile head load in the peak showed stable with the cycle number increasing, development and destruction of type three kinds of different forms of attenuation, reflection the pile of soil from elastic to plastic to the development process of destruction; the proportion of load of each row of pile group to share with the number of cycles are constantly changing, the load of the front pile sharing increases by bearing; Due to the constraint role of the platform, the axial cyclic tension and compression of the pile will cause serious settlement of pile groups accompanied by horizontal cyclic loading. The effect of load cycling on pile group's horizontal load is much larger than that of single pile.
(3) based on the 1 * 2 level steel pipe piles eccentric loading test, analyze the whole deformation of pile and pile internal force response, and through ABAQUS finite element simulation, discussed different eccentricity and pile layout size affected by the bearing characters of pile group horizontal eccentricity. The experimental results show that the force level of eccentric load the pile of pile group under the existence of great difference, from the loading point near the pile bear larger; due to horizontal and torsional load coupling effect in pile group pile, the torsion bearing capacity of single pile is increased; the additional torque pile head torque and horizontal shear resistance common horizontal load eccentricity the shear resistance of pile and pile group with torsion increases with the increase of the load. The numerical results show that the horizontal load eccentricity of the pile deformation is relatively small, but the effect on the internal force of foundation piles The layout of the pile significantly affects the level of the pile group and the anti overturning stiffness, but it has little influence on the whole torsional response of the pile group.
(4) 2 * 2 concrete pile group horizontal eccentric loading based on revealing the progressive failure process of pile group, the internal force of pile changes with load were studied with numerical analysis, and the concrete pile failure process at the level of eccentric load and mechanism are summarized. The research results show that high the loading height, weight of the upper structure and the pile of concrete cracking and other factors exacerbated the level of pile group under eccentric load overturning failure; pile group in the initial stage of loading in elastic state, the pile's horizontal stiffness is bigger; when the load exceeds a certain critical value of concrete pile has crack, pile group the stiffness decreases, the deformation increases; P- delta effect caused by the weight of the superstructure load to bear axial load in front of pile increases rapidly, the final front corner pile axial bias damage group The pile and its superstructure will be overturned as a whole.
(5) by the Zhejiang University ZJU-400 geotechnical centrifuge, carried out in sand pile under horizontal and eccentric load series model test, focuses on the comparative study of straight pile and pile group pile characteristics under different loading conditions of deformation and bearing. Test results show that the inclined pile horizontal and torsional bearing capacity were significantly higher than straight pile; the pile in pile group under eccentric load level of the pile top displacement difference than the straight pile more; inclined pile by pile axial load can effectively resist horizontal load. The numerical results show that the pile inclination on the pile horizontal bearing behavior of great influence pile group, horizontal stiffness increases with the increase of pile inclination increases.
(6) the analysis of pile group interaction model considering multi direction load; the rigid cap under the assumption that the expressions of the whole pile group stiffness matrix; coupling effect between different directions at the same time considering the effect of pile group pile and anisotropic load, discusses and induces a method for determining the pile stiffness calculation of anisotropy; summary the multi load flow analysis of pile groups under, and gives the corresponding examples.

【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU473.1

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