桩—土—复杂结构振动台试验与数值模拟及桩—土相关参数研究

发布时间：2018-08-12 15:31

【摘要】：城市交通日益拥挤，促进了地下空间的开发和利用，与地下空间开发相关的大型交通枢纽工程大量兴建，这些工程的抗震性能及其安全性，越来越受到学术界与工程界的关注。论文以天津站交通枢纽工程为背景，开展了大型桩-土-复杂结构的振动台模型试验，揭示了复杂动力相互作用体系(SSI)的有关规律；在试验的基础上研究了桩-土动力P-Y曲线；探索了桩-土界面的合理接触刚度因子取值范围问题，在此基础上进行了桩-土-复杂结构数值模拟计算，再现了振动台试验的过程，，与试验结果进行对比分析。完成的主要工作与结论如下：（1）选取天津站交通枢纽工程的典型七榀框架为研究对象，含地上与地下结构及群桩基础，进行了单向抗震性能试验研究。采用微粒混凝土制作车站结构模型；根据卓越周期相似比，设计并配置了模型土；在试验的刚性土箱中设计了三种边界，并验证了各自的良好效果；选择Taft波、天津波及人工波进行了小震到大震的多工况加载。试验结果表明：桩与土体的加速度放大系数在小震时大于1（或小于-1），大震时的放大系数明显减小，桩基的存在对放大系数有减小的影响；桩基的相对位移峰、净应变幅值及桩-土动接触压力幅值均随震级的增加而增大，同时，相对位移峰值随桩身高度增加而增大；净应变沿桩身高度呈现中间大、两端较小的趋势；与桩端相比，桩中间部位的动接触压力增加的最快；地上及地下结构的最大层间位移角在大震后满足规范限值要求。（2）根据振动台试验的结果，应用弹性地基梁理论得到了正弦波作用下的桩-土动力P-Y曲线，进而求得桩-土相互作用动力Winkler模型的弹簧刚度与阻尼沿桩身高度的变化规律及其受振动时间的影响。结果表明：阻尼系数与弹簧刚度系数都随着桩埋深的增加而增大，桩下部增大的幅度更加明显，受地下结构底部筏板的影响，阻尼与土弹簧刚度沿桩身分布可近似的考虑成分段线性，分段点大约在桩身上部1/3范围处；随着地震动的持续，阻尼系数基本稳定，只在桩底处略有增大，而弹簧刚度随振动时间持续有所降低，并且随埋深增大，其降低的幅度也越大。（3）对桩-土相互作用的界面接触问题进行了研究。将天津站交通枢纽工程的原型（及模型）单桩与土体考虑成平面应变问题，探索了基于罚函数法的接触刚度因子合理取值范围。结果表明：土体采用线弹性本构模拟时，下层单元厚度的减小及土体刚度的增加会使接触刚度增大，合理的接触刚度因子（FKN）取值范围会减小，但FKN整体取值在程序建议的范围（0.01~10）的前1/3以内；土体采用弹塑性本构模拟时，若土体处于弹性阶段，合理的FKN范围是对应的土体弹性模型的100倍，土体进入塑性以后，合理的FKN取值范围随着荷载的增加而减小。（4）建立了考虑桩-土界面接触的二维有限元模型，对比了三种地震波0.1g、0.3g及0.5g加载时的数值模拟与试验的加速度结果。结果表明：模拟与试验得出的测点加速度时程曲线波形相似，两者的测点加速度峰值随震级与高度的变化表现出了相同的规律，相对桩基而言，二维接触模型能更好地反应地下结构的加速度反应规律。论文还采用三维有限元模型进行了计算，计算结果表明，天津波0.1g加载时，三维有限元模型得到的测点加速度时程曲线与试验基本吻合，随着震级的增加，加速度峰值误差增大。
[Abstract]:Urban traffic congestion has promoted the development and utilization of underground space. Large-scale transportation hub projects related to underground space development have been constructed in large numbers. The seismic performance and safety of these projects have attracted more and more attention from academia and engineering circles.
In this paper, the shaking table model test of large-scale pile-soil-complex structure is carried out on the background of Tianjin Railway Station traffic hub project, and the relevant laws of complex dynamic interaction system (SSI) are revealed; the P-Y curve of pile-soil dynamic is studied on the basis of the test; and the reasonable range of contact stiffness factor of pile-soil interface is explored. On this basis, the numerical simulation of pile-soil-complex structure is carried out, and the shaking table test process is reproduced. The main work and conclusions are as follows:
(1) Seven typical frames of Tianjin Railway Station Transportation Junction Project were selected as the research objects, and the unidirectional seismic performance tests were carried out on the above-ground and underground structures and pile group foundations. Taft wave, Tianjin wave and man-made wave are selected to carry out multi-mode loading from small to large earthquakes. The test results show that the acceleration amplification coefficient of pile and soil is greater than 1 (or less than - 1) in small earthquakes, and the amplification coefficient decreases obviously in large earthquakes. The existence of pile foundation has an effect on the amplification coefficient. The relative displacement peak, the net strain amplitude and the dynamic contact pressure amplitude of pile-soil increase with the increase of earthquake magnitude, and the relative displacement peak increases with the increase of pile height. The maximum interlayer displacement angle of the upper and the underground structures meet the requirements of the specification limit after the great earthquake.
(2) Based on the results of shaking table test, the dynamic P-Y curve of pile-soil interaction under sinusoidal wave is obtained by using the theory of elastic foundation beam. The variation of spring stiffness and damping along pile height and the influence of vibration time are obtained by using the dynamic Winkler model of pile-soil interaction. The damping and soil spring stiffness distribution along the pile body can be approximately considered as a piecewise linear component, and the piecewise point is about 1/3 of the range of the pile body. The stiffness of the spring decreases with the increase of the buried depth and the vibration time.
(3) The interface contact problem of pile-soil interaction is studied. Considering the prototype (and model) of Tianjin Railway Station traffic hub project as a plane strain problem, the reasonable range of contact stiffness factor based on penalty function method is explored. The contact stiffness increases with the increase of soil stiffness and the reasonable range of contact stiffness factor (FKN) decreases, but the overall value of FKN is within the first 1/3 of the recommended range (0.01-10). If the soil is in the elastic stage, the reasonable range of FKN is 100 times of the corresponding soil elastic model. After the soil enters the plasticity, the reasonable value range of FKN decreases with the increase of load.
(4) A two-dimensional finite element model considering the pile-soil interface contact is established, and the results of numerical simulation and test acceleration of three kinds of seismic waves loaded at 0.1g, 0.3g and 0.5g are compared. The results show that the acceleration time-history curves obtained by simulation and test are similar, and the peak acceleration values of the measured points of the two kinds of seismic waves vary with magnitude and height. Compared with pile foundation, the two-dimensional contact model can better reflect the acceleration response of underground structure. The three-dimensional finite element model is used to calculate the acceleration response of underground structure. The calculation results show that the acceleration time-history curves obtained by the three-dimensional finite element model are basically consistent with the test results when the Tianjin wave is 0.1g loaded. The error of acceleration peak value increases.
【学位授予单位】：天津大学
【学位级别】：博士
【学位授予年份】：2013
【分类号】：TU473.1;TU435

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