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为了考察桩-土接触效应对结构地震反应的影响,利用有限元软件ABAQUS建立了土-桩-框架二维有限元模型,分别采用损伤塑性模型和动力粘塑性记忆型嵌套面模型模拟混凝土和土体,利用rebar单元模拟混凝土内的钢筋,取得了较好的计算效果.计算分析中采用19条不同频谱的地震波记录,考虑了地震动强度、桩径、摩擦系数等因素,以层间位移角和桩顶最大位移为主要评价指标,揭示相互作用体系的动力响应特性.分析认为,计算结果对桩、土摩擦系数的取值不敏感;不考虑土-桩接触时,近场土体的动力反应与实际情况存在一定的误差,且上部结构和桩基的动力反应会被低估,应该考虑桩-土动力接触效应;地震动强度增加时,随着结构进入塑性状态,低估程度减小;桩径增加时,低估程度没有显著变化,虽然桩基和上部结构的反应都有所减小. 相似文献
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桩-土-上部结构体系的动力相互作用是一个复杂的过程,尤其是在倾斜液化侧向扩展流动（侧扩流）场地中,由于地震过程中场地产生地面永久大变形,桩土间有可能产生错动滑移与开裂等非线性反应,因此桩-土相互作用模拟至关重要。为了探究桩-土非线性接触对倾斜液化场地-群桩基础-上部结构体系动力响应的影响,本文基于OpenSees分别建立了考虑桩-土相互作用弹簧和桩土结点之间直接绑定的有限元数值模型。结果表明：考虑桩-土相互作用Pyliq弹簧时,土体加速度幅值略微降低,桩基对土体的约束明显变弱,土体残余位移增大。同时,具有Pyliq弹簧的模型能较好地模拟桩的曲率响应,而采用桩土结点直接绑定的模型高估了桩顶曲率,进而无法准确估计桩基抗弯最不利位置。桩-土相互作用弹簧对上部结构动力响应的影响较小。 相似文献
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桩基-非线性框剪结构相互作用体系(下)-- 相互作用对结构地震反应的影响 总被引：1，自引：0，他引：1
本文研究桩基-非线性框剪结构相互作用体系的地震反应。其中上部框架和剪力墙结构分别用门型单元和四弹簧墙单元进行分析;桩基阻抗函数通过单桩阻抗和动力相互作用因于求得。采用频-时域混合法求解体系的动力方程,本文研究了在桩基-框剪结构相互作用体系地震反应分析中,桩基阻抗的频率相关性对结构地震反应的影响,并从土体剪切波速和地震波强度两个方面,研究了土-桩-结构相互作用对框剪结构地震反应的影响。 相似文献
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为了研究不同基础形式下河水对成层软土地基上建筑物地震反应的影响,构建了结构-基础-土-河水体系动力相互作用的非线性完全有限元计算模型,在考虑土体重力的前提下,对筏片基础、桩筏基础、箱形基础、桩箱基础相互作用体系进行了时域数值分析。计算结果表明,建筑物靠近河水时,筏基和箱基体系顶部位移发生了向河水一侧的偏移,而采用桩基和桩箱基础时其偏移度明显减小。同种基础形式下,建筑物距河水越远,其框架剪力峰值越大,而不同基础形式的同种工况,桩箱基础时柱剪力最大,筏片基础时最小。单纯筏基和箱基时,基础周围土体均大量进入塑性,上部结构仍保持弹性;而采用下部有桩基础的筏基或箱基时,地基土体只有很少量进入塑性,上部框架结构进入了塑性。 相似文献
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基于OpenSees数值分析平台,建立了群桩-土-桥墩非线性数值分析模型。模型中桩-土水平向相互作用和桩-土竖向相互作用、桩底-土竖向相互作用分别通过p-y、t-z与q-z零长度弹簧单元模拟。模型中同时考虑了群桩效应与纵筋在墩底的应变渗透和粘结滑移的影响。结合群桩基础拟静力试验结果,对数值模型的准确性进行了验证,在此基础上对土体参数特性对桩基滞回性能的影响规律进行了分析。结果表明:所建立的数值分析模型可对群桩基础滞回曲线和骨架曲线进行较为准确的模拟分析,验证了模型的可靠性。反复荷载作用下,前桩处土体的反应明显大于中桩处;土体由软黏土变为硬黏土时,墩顶侧向承载力与刚度显著增加,但土体的非线性反应减弱。 相似文献
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均匀土-桩基-结构相互作用体系的计算分析 总被引：14，自引：4，他引：14
本文以结构－地基动力相互作用振动台模型试验为基础，结合通用有限元软件ANSYS，对均匀土－桩基－结构动力相互作用体系进行了三维有限元分析。计算中土体采用等效线性模型，利用面－面接触单元考虑土体与结构交界面的状态非线性，计算与试验得出的规律基本一致。桩基与土体间发生了脱开再闭合和滑移现象。桩身应变幅值分布呈桩顶大、桩尖小的倒三角分布，角桩的应变幅值较大，边排中桩和中桩的应变幅值较小。桩土接触压力幅值呈桩顶小、桩尖大的三角形分布。在沿振动方向的三排桩中，边排桩的滑移比中排桩的滑移量大。通过计算分析与试验的对照研究，验证了采用的计算模型与分析方法的合理性，为结构－地基相互作用的进一步研究奠定了基础。 相似文献
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针对振动台试验,采用u-p形式控制方程表述饱和砂土的动力属性,选用土的多屈服面塑性本构模型刻画饱和砂土和黏土的力学特性,引入非线性梁-柱单元模拟桩,建立试验受控条件下液化场地群桩-土强震相互作用分析的三维有限元模型,并通过试验结果验证数值建模途径与模拟方法的正确性。以实际工程中常用的2×2群桩为例,建立桩-土-桥梁结构强震反应分析三维有限元模型。基于此,针对不同群桩基础配置对液化场地群桩-土强震相互作用影响展开具体分析。对比发现,桩的数量相同时,桩排列方向与地震波输入方向平行时比垂直时桩基受力减小5%~10%,而对场地液化情况无明显影响;相同排列形式下,三桩模型中土体出现液化的时间约比双桩模型延缓5s,桩上弯矩和剪力减小33%~38%。由此可见,桩基数量增加,桩-土体系整体刚度更大,场地抗液化性能显著,桩基对上部桥梁结构的承载性能明显增强,其安全性与可靠性更高。这对实际桥梁工程抗震设计具有一定的借鉴意义。 相似文献
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大直径扩底桩的地震反应分析对其抗震设计至关重要。本文采用ABAQUS有限元程序建立地震荷载作用下扩底桩-土-结构和普通等直径桩-土-结构动力相互作用体的三维有限元模型,分析大直径扩底桩与普通等直径桩地震反应的差异。桩周土采用Drucker-Prager弹塑性模型以考虑土体的非线性,桩体采用线弹性模型,桩与桩周土之间设置非线性接触。输入Imperial Vally地震波,对两种桩基的地震反应进行了数值计算,分析了桩土模量比、软夹层、上部质量等因素对桩基地震反应的影响。结果表明:与普通等直径桩相比,扩底桩的抗震性能没有明显提高,扩底直径对抗震性能影响不大,增大扩底桩直径,并不能提高扩底桩的抗震性能;上部结构的质量及桩土模量比对桩基的动力响应影响显著。 相似文献
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为研究强震作用下桩-土-断层非线性动力响应特性,依托海文大桥实体工程,选取4种类型(5010波、5002波、Kobe波和El-Centro波)地震波,通过建立桩-土-断层相互作用模型,利用MI?DAS/GTS有限元分析软件,研究断层上、下盘桩基加速度响应、桩顶水平位移、桩身弯矩以及剪力响应情况.结果表明:4种类型地震波... 相似文献
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In this paper, a soil–pile–structure model is tested on a shaking table subject to both a sinusoidal wave and the acceleration time history of the scaled 1940 El Centro earthquake. A medium-size river sand is compacted into a 1.7-m-high laminar rectangular tank to form a loose fill with a relative density of 15%. A single-storey steel structure of 2.54 ton is placed on a concrete pile cap, which is connected to the four end-bearing piles. A very distinct pounding phenomenon between soil and pile is observed; and, the acceleration response of the pile cap can be three times larger than that of the structural response. The pounding is due to the development of a gap separation between soil and pile, and the extraordinary large inertia force suffered at the top of the pile also induces cracking in the pile. To explain this observed phenomenon, nonlinear finite element method (FEM) analyses with a nonlinear gap element have been carried out. The spikes in the acceleration response of the pile cap caused by pounding can be modeled adequately by the FEM analyses. The present results suggest that one of the probable causes of pile damages is due to seismic pounding between the laterally compressed soil and the pile near the pile cap level. 相似文献
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The seismic response of pile foundations is a very complex process involving inertial interaction between structure and pile foundation, kinematic interaction between piles and soils, seismically induced pore-water pressures (PWP) and the non-linear response of soils to strong earthquake motions. In contrast, very simple pseudo-static methods are used in engineering practice to determine response parameters for design. These methods neglect several of the factors cited above that can strongly affect pile response. Also soil–pile interaction is modelled using either linear or non-linear springs in a Winkler computational model for pile response. The reliability of this constitutive model has been questioned. In the case of pile groups, the Winkler model for analysis of a single pile is adjusted in various ways by empirical factors to yield a computational model for group response. Can the results of such a simplified analysis be adequate for design in all situations?The lecture will present a critical evaluation of general engineering practice for estimating the response of pile foundations in liquefiable and non-liquefiable soils during earthquakes. The evaluation is part of a major research study on the seismic design of pile foundations sponsored by a Japanese construction company with interests in performance based design and the seismic response of piles in reclaimed land. The evaluation of practice is based on results from field tests, centrifuge tests on model piles and comprehensive non-linear dynamic analyses of pile foundations consisting of both single piles and pile groups. Studies of particular aspects of pile–soil interaction were made. Piles in layered liquefiable soils were analysed in detail as case histories show that these conditions increase the seismic demand on pile foundations. These studies demonstrate the importance of kinematic interaction, usually neglected in simple pseudo-static methods. Recent developments in designing piles to resist lateral spreading of the ground after liquefaction are presented. A comprehensive study of the evaluation of pile cap stiffness coefficients was undertaken and a reliable method of selecting the single value stiffnesses demanded by mainstream commercial structural software was developed. Some other important findings from the study are: the relative effects of inertial and kinematic interactions between foundation and soil on acceleration and displacement spectra of the super-structure; a method for estimating whether inertial interaction is likely to be important or not in a given situation and so when a structure may be treated as a fixed based structure for estimating inertial loads; the occurrence of large kinematic moments when a liquefied layer or naturally occurring soft layer is sandwiched between two hard layers; and the role of rotational stiffness in controlling pile head displacements, especially in liquefiable soils. The lecture concludes with some recommendations for practice that recognize that design, especially preliminary design, will always be based on simplified procedures. 相似文献
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The paper presents a numerical model for the dynamic analysis of pile groups with inclined piles in horizontally layered soil deposits. Piles are modelled with Euler–Bernoulli beams, while the soil is supposed to be constituted by independent infinite viscoelastic horizontal layers. The pile–soil–pile interaction as well as the hysteretic and geometric damping is taken into account by means of two‐dimensional elastodynamic Green's functions. Piles cap is considered by introducing a rigid constraint; the condensation of the problem permits a consistent derivation of both the dynamic impedance matrix of the soil–foundation system and the foundation input motion. These quantities are those used to perform inertial soil–structure interaction analyses in the framework of the substructure approach. Furthermore, the model allows evaluating the kinematic stress resultants in piles resulting from waves propagating in the soil deposit, taking into account the pile–soil–pile interactions. The model validation is carried out by performing accuracy analyses and comparing results in terms of dynamic impedance functions, kinematic response parameters and pile stress resultants, with those furnished by 3D refined finite element models. To this purpose, classical elastodynamic solutions are adopted to define the soil–pile interaction problem. The model results in low computational demands without significant loss of precision, compared with more rigorous approaches or refined finite element models. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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Nonlinear lateral interaction in pile dynamics 总被引：4，自引：0，他引：4
A model for pile lateral response to transient dynamic loading and to harmonic loading is presented allowing for nonlinear soil behaviour, discontinuity conditions at the pile-soil interface and energy dissipation through different types of damping. The approach is used to establish equivalent linear stiffness and damping parameters of single piles as well as dynamic interaction factors for approximate nonlinear analysis of pile groups. The applicability of these parameters to the pile-group analysis was examined, and a reasonable agreement with the direct analysis was found. The superposition technique may be used to analyze the response of small pile groups. Also, the dynamic stiffness of pile groups is greatly affected by both the nonlinear behavior of the soil and the slippage and gapping between the pile and soil. For a basic range of soil and pile parameters, equivalent linear stiffness and damping parameters of single piles and interaction factors for approximate nonlinear analysis are provided. 相似文献
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The dynamic response of a seismic soil–pile–structure interaction (SSPSI) system is investigated in this paper by conducting nonlinear 3D finite element numerical simulations. Nonlinear behaviors such as non-reflecting boundary condition and soil–pile–structure interaction modeled by the penalty method have been taken into account. An equivalent linear model developed from the ground response analysis and the modified Drucker–Prager model are separately used for soil ground. A comparison of the two models shows that the equivalent linear soil model results in an underestimated acceleration response of the structure under this ground shaking and the soil behavior should be considered as a fully-nonlinear constitutive model in the design process of the SSPSI system. It was also observed that the dynamic response of the system is greatly affected by the nonlinearity of soil–pile interface and is not sensitive to the dilation angle of the soil. Furthermore, the effect of the presence of pile foundations on SSPSI response is also analyzed and discussed. 相似文献
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爆破地震作用下桩-土-结构相互作用的数值模拟 总被引：1，自引：0，他引：1
土-结构动力相互作用是地震工程和结构抗震的重要研究内容,但目前对爆破地震作用下土-结构动力相互作用的研究较少。运用大型有限元软件ANSYS/LS-DYNA,建立了桩-土-结构相互作用体系的三维有限元模型,由桩尖输入实测爆破地震波,取得了良好的计算效果。计算结果表明：考虑桩-土-结构相互作用后,群桩基础中每个桩的位移、加速度和剪应力幅值均呈桩顶大、桩尖小的倒三角分布,桩与承台的接合部比较容易受到损坏;桩-土-结构相互作用体系在爆破地震波冲击后,还会发生几次振动,但是这些振动产生的影响要小于爆破地震产生的影响,这与实测结果相符合;爆破地震波冲击下,群桩基础中,角桩顶部表面的桩土接触压力较大,但在爆破地震波冲击后,中心桩顶部表面的桩土接触压力较大,且具有一定的周期性,直至衰减为零。 相似文献
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The present study aims at investigating the nonlinear behavior of single hollow pile in layered soil subjected to varying levels of horizontal dynamic load. A finite element model has been developed using commercially available FEM based software. Mohr–Coulomb plasticity model is used to simulate the soil plasticity whereas the pile-material is idealized as elastic. Numerical results are validated comparing with the experimental results. The experimental investigations were carried out in the field located at IIT Kharagpur. Two types of motion: horizontal and rocking are studied. The effects of various influencing parameters, namely, exciting moment, length and diameter of the pile etc. on the nonlinear dynamic response of piles are investigated. It is found that separation of pile from the surrounding soil considerably affects the resonance frequency and amplitude of the pile foundations. 相似文献
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为研究液化场地变截面桩的动力响应,依托翔安大桥实体工程,采用有限元软件,建立变截面桩－土和等截面桩－土相互作用模型,模拟液化场地变截面桩及等截面桩在地震作用下的振动反应,分析在地震作用下变截面位置不同的变截面桩及等截面桩的动力响应特征。结果表明:地震作用下,液化土层不同深度处的孔压比变化规律基本相同,均从0逐渐增大最后趋于稳定;变截面桩的桩身加速度和桩身位移均大于等截面桩,且桩顶加速度峰值出现的时刻均滞后于桩底;在饱和砂土层处,桩身位移变化趋势均较陡;变截面桩的桩身弯矩峰值和桩身剪力峰值均大于等截面桩,且其峰值出现的位置较等截面桩深;地震作用下,变截面桩及等截面桩的弯矩与剪力均在安全范围之内;液化场地变截面梁桥桩基础抗震设计时,应着重分析液化土层与非液化土层分界面以下的抗弯能力设计及液化土层中抗剪能力设计。 相似文献
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B. K. Maheshwari K. Z. Truman M. H. El Naggar P. L. Gould 《Soil Dynamics and Earthquake Engineering》2004,24(4):343-356
A three-dimensional method of analysis is presented for the seismic response of structures constructed on pile foundations. An analysis is formulated in the time domain and the effects of material nonlinearity of soil on the seismic response are investigated. A subsystem model consisting of a structure subsystem and a pile-foundation subsystem is used. Seismic response of the system is found using a successive-coupling incremental solution scheme. Both subsystems are assumed to be coupled at each time step. Material nonlinearity is accounted for by incorporating an advanced plasticity-based soil model, HiSS, in the finite element formulation. Both single piles and pile groups are considered and the effects of kinematic and inertial interaction on seismic response are investigated while considering harmonic and transient excitations. It is seen that nonlinearity significantly affects seismic response of pile foundations as well as that of structures. Effects of nonlinearity on response are dependent on the frequency of excitation with nonlinearity causing an increase in response at low frequencies of excitation. 相似文献
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The influence of nonlinearity on the dynamic response of cast-in-situ reinforced concrete piles subjected to strong vertical excitation was studied. Forced vibration test of single piles (L/d=10, 15, 20) and 2×2 pile groups (s/d=2, 3, 4 for each L/d) were conducted in the field for two different embedded conditions of pile cap. From the measured nonlinear response curves, the effective pile–soil system mass, stiffness and damping were determined and the nonlinear response curves were back-calculated using the theory of nonlinear vibration. The test results were compared with the continuum approach of Novak with dynamic interaction factor approach using both linear and linear-equivalent numerical methods. Reasonable match between the measured and predicted response was found for linear-equivalent methods by introducing a weak boundary-zone around the pile to approximately account for the nonlinear behaviour of pile–soil system. The test data were used to establish the empirical relationship in order to estimate the extent of soil separation around the pile with soil under vertical vibration. 相似文献