【作者】 杨小卫；

【导师】 胡春林；

【作者基本信息】 武汉理工大学 ， 岩土工程， 2006， 硕士

【摘要】 桩基是一种历史悠久而又被广泛采用的基础型式。历次世界大地震中,均出现了各类桩基础的严重破坏现象。由于破坏的隐蔽性,使得已破坏桩基的修复极为困难而且耗资巨大。在现有桩基抗震设计规范中提出了一些桩基抗震的构造措施,但缺乏系统性和针对性。试验表明,在地震作用下,地基与结构之间存在很强的动力相互作用。对地震作用下土—桩—结构动力相互作用进行数值模拟研究具有重要的学术意义和工程实用价值。 作者对桩的震害特点、破坏形式、桩—土—结构动力相互作用的分析方法等几个方面进行了系统地总结。地震作用下桩—土—结构动力相互作用是一个多学科交叉,多部门关注的复杂课题。针对不同的具体问题,一方面要改进与发展理论严密的精细分析方法,同时也要发展计算模型简单、参数便于确定的实用性较强的简化分析方法,以满足不同工程的抗震设计要求。本文采用动力有限元分析方法,将研究体系简化为平面模型,重点研究了桩—土—结构动力相互作用体系的动力特性和基桩的抗震性能等,主要开展了如下工作: (1) 选择适合桩—土—结构动力相互作用分析的材料本构关系,研究了桩—土—结构动力相互作用体系二维有限元分析的一种实用方法。上部结构采用线弹性的本构模型,下部土体采用等效非线性本构关系或基于Drucker-Prager屈服准则的弹塑性模型,确定了相应模型的矩阵及模型所需的相关参数。探讨了非线性动力方程的求解方法,单元的选取,土体边界的模拟方法,网格大小的划分,重力的考虑等。 (2) 进行了不同输入地震动、不同场地条件下桩土体系的地震反应分析及地震作用下桩土体系的参数敏感性分析:探讨了在地震作用下考虑土体弹塑性时桩土体体系的动力相互作用。既使在相同地质条件、相同地震动加速度峰值的条件下,如果输入地震波的波形不同,得到的桩土体系的地震反应也不同,并对放大倍数或高频过滤产生影响。桩土体系上部土体的刚度越大,桩身的水平位移、加速度越小,但对较深处桩的位移和加速度的影响较小。调整相应的模型参数进行多因素敏感性分析,得到桩土模量比对桩顶水平位移及桩身最大弯矩的影响最大,地震动的输入水平次之、桩的长径比影响较小。在土体基本弹性参数不变时,考虑土体弹塑性后,桩身的水平相对位移、加速度和剪力均可能减小;在水平地震作用下,单层土体的破坏表现为剪切型特性,而多层土体更多还原

【Abstract】 Pile foundation has been used to consolidate soft ground for a long history, and it is also one popular means to be used to improve foundation today. Many pile foundations were damaged seriously during the past major earthquakes. Large amount of cost have been paid for the remedy of pile foundation after earthquakes .The code for seismic design of pile only made some details of seismic design, the lack of gender. Significant testing and analysis found in the role of the earthquake, the interaction between the foundation and structure occur. So it is a significant value for both academic and concrete project to study the subject of numerical modeling of pile - soil -superstructure dynamic interaction under seismic loading.Based on the review of past research work, a state-of-art with respect to pile-soil-superstructure dynamic interaction, which includes piles earthquake disaster characteristics and damage forms, pile-soil-structure interaction analysis methods, is presented firstly. Research field of pile-soil-superstructure dynamic interaction under seismic loading is a complicated program involving many subjects, and also concerned by many departments. To meet the different requirements of structure anti-seismic design, it is necessary to develop both rigorous model and simplified model. Because of this, with the method of whole dynamic finite element, the study will simplify the system for the horizontal model, through a comparative analysis, and examined the pile-soil-structure interaction system for dynamic characteristics and laws for the following:(1) The suitable constitutive equation for pile-soil-structure is selected, and the practical analysis model of the finite element method is adopted in the study of pile-soil- structure dynamic interaction. The elastic constitutive model is used for the superstructure, and the elastic-plastic constitutive model based on Drucker-Prager yield criterion is used for the soil, then the parameters for these constitutive models are computed .The solution of motion equation, the finite element, the boundary of soil, the dimension of mesh and the gravity load of system are discussed in this paper.(2) Pile-soil dynamic interaction under the different seismic wave and site conditions, multiple factors and levels parametric sensitivity analysis of pile-soil system, Pile-Soil dynamic interaction under seismic dynamic load and the elastic-plastic property of soil have been discussed. Then under the same siteconditions and the same peak value of seismic accelerated speed, the seismic response of the pile-soil dynamic interaction is different if the shape of the seismic wave differs. The harder the upper soil is, the more the displacement and accelerated speed of the pile are decreased. But it affects less to the deep pile. Among these factors, pile soil stiffness ratio, pile slenderness ratio and earthquake design level are taken into consideration. The calculation results indicate that the pile soil stiffness ratio is the most sensitive one among three factors. In the same elastic parameters of soil, when the elastic-plastic property of soil has been considered, the displacement, accelerated speed and the shear of the pile are decreased probably. Under the horizontal seismic action, the single-deck soil damaged turns to be sheared;multi-layer soil turns to be curved scissors. Because of pile existence, the displacement, accelerated speed of pile-surrounding soil would be greatly reduced.(3) In the pile-soil-superstructure dynamic interaction analysis, it emphasizes the seismic response on the pile in liquefiable site. With the deepening of the liquefiable soil, the inherent vibration periodic time, peak value of horizontal displacement in the pile and the peak value of moment and shear on the top of pile are increasing. At the meantime, influence of seismic response on piles due to pile-surrounding soil and spacing between adjacent piles was studied. The peak value of horizontal displacement in the pile appears to the top of pile. When the thickness of the upper soft soil layer is little ,the internal force of the pile body at the top of pile section would reach the maximum value .When the thickness of the upper soft soil layer reach a certainty value, the internal force of the pile body at soil-hard demarcation section would reach the maximum value. The internal force peak value of pile body would be decreased with reducing spacing of the pile. At the same time, these infer force on the pile section at the first movement of the soft soil and hard soil is largely increasing. With increasing of stiffness of superstructure, the inherent vibration periodic time is decreased, and the peak value of horizontal displacement in the pile and the peak value of moment and shear on the top of pile are increasing. Pile soil stiffness ratio, pile slenderness ratio and earthquake design level are the three factors of the sensitivity. At last, two-dimension seismic and the interaction have been discussed. It is discovered that the value of decrease for the story drift, relative displacement, the shear force and axial force of column are different. So the same decrease of the value for different those parameters in the Code for seismic design of buildings is not reasonable.In the anti-seismic design of buildings, not only should pile-raft foundations anchoring and details of seismic design be noticed, but also special attention should be paid to the pile section’s moment of resistance steel and shear of resistance steel at the first movement of the soft soil and hard soil in order to prevent it from curved scissors damaging.更多还原