桩基础水平响应计算方法及其抗液化性能研究

发布时间：2018-03-29 11:55

本文选题：桩基础　切入点：应变楔形体模型　出处：《大连理工大学》2013年博士论文

【摘要】：桩基础在当前日益发展的土木工程基础设施建设中得到了广泛的应用,而桩基础不仅仅承担着竖向荷载,同时也会承担水平向荷载,特别在地震过程中,桩头所支撑的上部结构会产生很大的惯性力,使得钢筋混凝土桩很容易进入非线性状态,从而产生破坏,因此,如何合理地建立水平加载条件下考虑钢筋混凝土桩的材料非线性的静力分析方法是桩基础抗震设计中重要的研究课题,对于软土地区的水平加载桩,桩与其后侧粘土的分离对桩基础的水平承载性能有很大影响,如何在计算中考虑这一影响尚待研究,同时,对于软土地区的桩基础会涉及到地基改良问题,如何确定经济有效的改良深度也是个研究课题,另外,目前对于群桩基础的水平承载力设计方法还不够完善,需要做进一步研究,同时,在地震过程中,饱和砂土场地会产生砂土液化现象,而目前对于液化场地上群桩基础抗液化性能的研究甚少,也是需要进一步开展的工作。本文围绕着桩基础做了以下研究工作： (1)针对现有的应变楔形体模型存在的缺点,如楔形体前破坏面不连续、应力应变路径的公式比较复杂且参数不易选取、不适用于超固结粘土的计算等,本文提出了修正的应变楔形体模型以用于桩基础的水平响应的计算,编制了SWPILE有限元程序,并通过已有文献中大量的砂土、粘土以及层状土中水平加载桩试验,验证了该修正模型的可行性,并讨论了应变楔形体模型中的收敛问题、楔形体中应变和楔形体高度变化规律以及参数的敏感性等,最后,利用该修正的应变楔形体模型研究了p-y曲线的影响因素； (2)基于修正的应变楔形体模型,研究了双层地基(密砂土和软粘土)中桩基的水平响应,并研究了土的成层效应对桩基水平响应的影响规律,包括密砂土中的软粘土夹层和软粘土中密砂土夹层,在此基础上,分析了密砂土场地和软粘土场地中地表土层最大影响深度及其与计算出的楔形体高度的关系； (3)在修正的应变楔形体模型中,采用纤维单元实现了水平加载条件下考虑钢筋混凝土桩的材料非线性的计算,并根据已有文献中的水平加载桩试验资料和计算结果,验证了该计算方法的可行性。利用该方法研究了钢筋混凝土桩截面刚度在水平荷载作用下的变化规律以及桩的材料非线性对桩的挠度以及最大弯矩的影响；采用了单元应力磨平的方法把纤维单元高斯点的应力恢复到截面网格节点上,并绘制了截面的应力云图,从而了解了中性轴在不同荷载下的变化以及混凝土开裂的发展情况； (4)在修正的应变楔形体模型中引入了p-y乘子的概念来考虑群桩效应,并综合了应变楔形体模型和Mokwa等效单桩法的优点,提出了改进的等效单桩法,通过已有文献中的水平加载单桩与群桩实验,验证了该方法的有效性,并基于该方法,研究了p-y乘子对不同位置(排)桩工况中计算出的p-y曲线的影响,并分析了不同深度处以及不同位置(排)桩工况中计算出的粘土和砂土的极限地基反力,还研究了水平荷载和场地深度对群桩效应的影响以及不同桩头条件对单桩和群桩基础水平响应的影响； (5)初步研究了液化场地桩基础水平响应计算方法。基于完整的震后房屋损坏调查资料,应用完全耦合的动力有限元方法再现了由砂土液化引起的房屋破坏情况,利用修正的Pastor-Zienkiewicz Mark-Ⅲ模型来模拟砂土在地震荷载作用下的液化特性,用三轴试验结果和标准贯入数据来确定该模型参数,根据一组竖向分布的加速度传感器记录,采用SHAKE91程序确定了地震动输入,并把有限元计算出的地表水平位移与已有文献中经验公式计算出的结果以及震害调查的结果进行了比较,从而验证了有限元计算结果的合理性,随后,通过一系列的工况分析了边坡对房屋震害的影响,并对比研究了群桩、水泥土、排水系统的抗液化性能,为液化场地上群桩基础设计提供了计算方法和参考依据。
[Abstract]:Pile foundation has been widely used in the current development of the civil engineering infrastructure construction, and the pile foundation not only bear vertical load, but also bear the horizontal loads, especially during the earthquake, the upper structure supported by pile head will have a great inertia, the reinforced concrete pile easily into nonlinear the state, resulting in failure, therefore, how to establish the level of loading conditions considering material nonlinear static analysis method of reinforced concrete pile is an important research topic in the seismic design of pile foundation, the horizontal loaded pile in soft soil area, and the rear side of the clay pile separation level on pile foundation bearing performance greatly. How in the calculation of the influence is to be studied, at the same time, for the pile foundation in soft clay foundation improvement will involve the problem, how to determine the economic and effective reform Is a good research topic, also the depth, the horizontal bearing capacity of pile foundation design method is still not perfect, need to do further research, at the same time, during the earthquake, liquefaction of saturated sand ground will produce the phenomenon, but the research on liquefaction liquefaction resistance of pile foundation is very little, also need to be further the work carried out around the pile foundation. This paper does the following research work:
(1) according to the existing strain wedge model of the existing shortcomings, such as wedge before failure surface discontinuity, stress strain path formula is complicated and it is difficult to select parameters, not suitable for overconsolidated clay calculation, calculation is proposed in this paper. The strain wedge model modified for pile foundation level in response, the SWPILE finite element program, and through a large number of literatures in the sand, clay and horizontal layered soil loading pile test, verify the feasibility of the modified model, and discussed the convergence of strain wedge model, strain wedge and wedge height and the variation of parameter sensitivity finally, study the influence factors of p-y curve using the strain wedge model of the correction of the;
(2) the strain wedge model based on the study of double layered soil (dense sand and soft clay) in the lateral response of pile foundations, and studied the effects of pile horizontal layer effect response of the soil, including soft clay interlayer in dense sand and soft clay in dense sand interlayer, on the basis of analysis of dense sandy soil, ground and surface soil in soft clay and its maximum influence depth and calculate the wedge height relationship;
(3) in the modified strain wedge model, using the fiber element material nonlinear reinforced concrete pile considering the horizontal loading conditions, and according to the existing literature in the pile loading test data and calculation results, verify the feasibility of the method. The reinforced concrete pile section stiffness change the law under the action of horizontal load and deflection of pile pile material nonlinear and maximum bending moment effect by using this method; using unit stress to smooth fiber element Gauss points stress recovery section to nodes in the grid, and the section stress nephogram drawing, so as to understand the changes in the neutral axis under different loads, the crack of the concrete development;
(4) the strain wedge model modified in the concept of the p-y multiplier to consider the effect of pile group, and the comprehensive advantages of strain wedge model and Mokwa equivalent single pile method, improved equivalent single pile method, the horizontal loading in the literature of single pile and pile group experimental verification the effectiveness of the proposed method, and based on this method, the p-y multiplier in different position (row) p-y curve calculated in the condition of pile, and analyzes the different depth and different position (row) to calculate the pile condition in clay and sand limit subgrade reaction, are also studied influence of horizontal load and depth of field effect of pile group and different pile head conditions on single pile and pile group foundation level response;
(5) a preliminary study on the calculation method of pile foundation response level. After the complete housing damage based on investigation data, the dynamic finite element method fully coupled application reproduced by sand liquefaction caused by the destruction of houses, to simulate the characteristics of sand liquefaction under seismic loading using Pastor-Zienkiewicz Mark- III model, with the results three axis test and standard penetration test data to determine the model parameters according to the acceleration sensor records a group of vertical distribution, using SHAKE91 program to determine the seismic input, and compares the empirical formula of finite element to calculate the surface horizontal displacement and the calculated results and the results of earthquake damage investigation, rationality, and to verify the finite element calculation results subsequently, effect of slope on building damage are analyzed through a series of conditions, and compared the research group The anti liquefaction properties of pile, cement soil and drainage system provide the calculation method and reference for the design of pile group foundation on the liquefied site.

【学位授予单位】：大连理工大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TU473.1

【参考文献】