均匀土-桩基-结构相互作用体系的计算分析

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。     

考虑土-结构相互作用的高层建筑抗震分析

本文采用通用有限元程序ANSYS,针对上海地区一例土-箱基-高层建筑结构进行了三维有限元分析,计算中土体的本构模型采用等效线性模型,利用粘一弹性人工边界作为土体的侧向边界,并研究了土体边界位置、土性、基础埋深、基础形式以及上部结构刚度等参数对动力相互作用体系动力特性及地震反应的影响。     

结构-基础-土-河流相互作用地震反应分析

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。     

用ANSYS模拟结构-地基动力相互作用振动台试验的建模方法

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，对结构－地基动力相互作用体系进行有限元计算建模的一些问题作了研究，主要包括柔性土容器的模拟、土体动力本构模型的选用、土体与结构交界面上的状态非线性模型、网格划分、重力的考虑、结构中钢筋的处理以及对称性的应用等。文中给出了利用上述建模方法对结构－地基动力相互作用体系进行计算的一些加速度时程结果，并与试验结果相对照，吻合较好。通过计算分析，验证了简化处理方法的合理性和计算模型的可行性。     

埋地管线数值模拟中土体计算区域的选取问题研究

详细论述了动力无限元基本理论，提出了一种在非一致激励时无限元边界面上地震动的输入方法。在此基础上，考虑管线-土体之间的黏结滑移效应，采用动力无限元边界，建立了埋地管线的三维有限元-无限元耦合的精细化模型，对非一致地震波激励下埋地管线的动力响应进行了数值分析，对管线周围的土体计算范围的取值进行了系统研究，给出了管线周围土体的有效计算宽度W、有效计算长度L和有效计算深度H的取值范围。结果表明：W的取值与管径D紧密相关，H可取30～60 m,L应至少包含一个地震动的卓越周期段的波长，此分析结果可满足大多数工程需求。     

高层建筑-基础-土体耦合系统的动力分析

本文应用半解析元方法对高层建筑-基础-土体耦合系统进行了动力分析。结构、基础和土体均采用三维连续体模型,在水平两方向解析、竖向离散。这样既考虑了系统的三维效应,又可大大节省计算工作景,计算可以在微机上实现,为探讨结构-基础-土体相互作用的内在机理提供了一个途径。     

接触对桩-土-结构动力相互作用体系的影响

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.     

高耸混凝土烟囱土-结构相互作用地震反应分析

目前在高耸混凝土烟囱结构抗震设计和抗震性能评估中,由于缺乏合适的计算模型,一般采用刚性地基假定而忽略土-结构相互作用效应,或者采用传统的集中参数模型而忽略土的非线性特性。针对此不足,本文选用240 m高的钢筋混凝土烟囱作为研究对象,采用OpenSees程序,基于非线性文克尔地基梁模型和基于柔度法的分布塑性梁柱单元,建立了土体-基础-上部结构共同工作的整体非线性有限元分析模型,详细介绍了非线性文克尔地基梁模型主要参数的确定方法;研究了地基土非线性对高耸烟囱结构地震反应的影响,给出了考虑土-结构相互作用效应后结构周期、上部结构的内力和变形分布的变化规律。分析结果表明:考虑土-结构相互作用后,结构的自振特性、内力及节点位移都发生了不同程度的改变;考虑土体非线性特性的土-结构相互作用模型,峰值截面弯矩、剪力及截面曲率延性系数与不考虑土-结构相互作用时的结果之比分别介于0.921~1.219、0.732~1.29和0.822~1.536;而不考虑土体非线性特性的土-结构相互作用模型,峰值截面弯矩、剪力及截面曲率延性系数与不考虑土-结构相互作用时的结果之比分别介于0.838~1.578、0.92~1.76和0.656~2.831。不考虑土体非线性特性的土-结构相互作用模型的峰值截面弯矩、剪力及截面曲率延性系数的取值总体上较大,高估了烟囱结构在地震荷载作用下的内力需求。     

土-结构动力相互作用人工边界分析及试验验证

利用有限元软件Ansys二次开发语言apdl进行二次开发,将多次透射边界(MTF边界)和弹阻边界(V-S边界)添加到软件中,从而实现对土-结构动力相互作用问题中无限域场地的模拟。以野外大比例(1/2)土-箱基-框架结构试验模型的牵引释放自由振动试验(波源问题)和爆破震动试验(散射问题)数据为基础,通过有限元数值计算结果和试验结果的对比可知,施加了人工边界的土体模型可以较好地模拟波在无限域土体中的传播,有效地减少有限元计算模拟时的计算规模。同时多次透射边界在计算精度以及散射问题中地震波输入的便捷性方面要优于弹阻边界。     

土-桩-框架结构非线性相互作用的精细数值模型及其验证

利用有限元软件ABAQUS,建立了土-桩-框架结构非线性相互作用（SSI）的二维精细有限元模型,分别采用记忆型粘塑性嵌套面模型和损伤塑性模型模拟土体和混凝土材料,采用梁单元和rebar单元模拟RC桩基及其内部纵筋,采用接触面对法模拟桩土接触效应,取得了良好的计算效果。将自由场、框架、土-桩-框架结构模型的分析结果和其它成熟的计算软件进行对比,验证了数值模型的有效性。分析发现：桩基外侧靠近承台处的土体的非线性反应很强烈,而桩基内部土体的非线性反应较小,很大程度上只是跟随群桩一起运动。由于桩土动力接触,桩顶的加速度反应可能超出上部结构,并且桩顶的加速度时程曲线上有非常明显的＂针＂状突变。随着地震动强度的增加,上部框架逐渐表现出单自由度体系的动力特征,加速度反应谱有从多个波峰退化为单一波峰的趋势。     

Separation and sliding between soil and structure during strong ground motion

This paper presents an approach to the problem of separation and sliding between soil and structure in the finite element analysis of dynamic soil-structure interaction problems. Joint elements are arranged along the contact surface between soil and structure and they have a property such that tensile forces are not transmitted between the planes representing structure and soil in the finite element analysis. The dynamic properties governing the sliding are determined by the Mohr-Coulomb failure law determined from the cohesion and the friction angle between soil and structure. The proposed method is applied to (i) a model of a reactor building resting on the free surface of layered ground and (ii) a buried foundation structure. The numerical computations reveal the following results: that the translation is dominant in the motion of the structure when sliding is taking place between soil and structure, and that the rocking is dominant in the rest of the response. The amplitude of the response during sliding is increased on any one point of the structure and decreased on any one point of the ground compared with that of the fixed condition at the interface. In the case of the buried structure, it is observed in the computed results that the structure and soil move in the opposite direction along the vertical contact surface and are separated from each other in the near surface region during the strong phase of the excitation.     

轨道交通荷载下桩板结构主动隔振效果研究

为了研究在轨道交通荷载作用下桩板结构主动隔振措施的隔振效果,通过无限元边界与有限元边界相结合的有限元分析方法在路基中建立桩板结构模型,并在沙土地基中设置混凝土桩板结构进行模型试验,通过模型试验对有限元数值模拟结果加以验证,将桩长、埋深及置换率3个因素考虑在内,研究其对隔振效果的影响。结果表明:模型试验验证有限元计算方法的可靠性;随桩长增加振幅降低比减小,隔振效果明显,随着振源距离增加其振幅降低比减小明显;埋深为桩板结构主动隔振措施中的主要影响因素,随着埋深增加振幅降低比明显减小,隔振效果越明显;有限元计算过程中置换率对隔振效果的影响不明显,但是在模型试验中置换率对隔振效果影响较显著。     

基坑排桩对建筑抗震性的影响分析

以往对建筑抗震性影响因素的研究仅限于施工材料、技术手段等外部条件,忽略了基坑土体安全系数、基坑状态对建筑抗震性的影响,一定程度上削弱了建筑的抗震性能。本文从基坑排桩角度对建筑抗震性的影响展开分析,通过有限元强度折减法获取土体的安全系数与基坑状态的判断标准,在该标准下基于土体安全系数采用有限元强度折减法计算公式,获取各个土层计算参数。基于该参数使用ABAQUS有限元软件构建基坑排桩有限元分析模型(土体和桩体分别采用莫尔-库仑弹塑性模型和二维弹性模型)。实验采用所提分析方法,从基坑排桩排距、刚度两方面对建筑抗震性能进行分析。实验结果表明,当基坑排桩排距进行适当取值时,建筑抗震性越好;双排桩的刚度越大,建筑抗震性越好,且随着刚度的增加建筑抗震性能趋于平稳。     

Interaction of foundation−structure systems with seismically precarious slopes: Numerical analysis with strain softening constitutive model

This paper studies the combined effects of earthquake-triggered landslides and ground shaking on foundation−structure systems founded near slope crests. Plane-strain nonlinear finite element dynamic analyses are performed. The soil constitutive model is calibrated against published data to simulate the (post-peak) softening behavior of soil during a seismic event and under the action of gravitational forces. The plastic shear zones and the yield accelerations obtained from our dynamic analyses are shown to be consistent with the slip surfaces and the seismic coefficients obtained by classical pseudostatic limiting equilibrium and limit analysis methods. The foundation and frame columns and beams are modeled as flexural beam elements, while the possibility of sliding and detachment (separation) between the foundation and the underlying soil is considered through the use of special frictional gap elements. The effects of foundation type (isolated footings versus a rigid raft) on the position of the sliding surface, on the foundation total and differential displacements, and on the distress of the foundation slab and superstructure columns, are explored parametrically. It is shown that a frame structure founded on a properly designed raft could survive the combined effects of slope failure and ground shaking, even if the latter is the result of a strong base excitation amplified by the soil layer and slope topography.     

Impedance of flexible suction caissons

The dynamic response of offshore wind turbines is affected by the properties of the foundation and the subsoil. The aim of this paper is to evaluate the dynamic soil–structure interaction of suction caissons for offshore wind turbines. The investigations include evaluation of the vertical and coupled sliding–rocking vibrations, influence of the foundation geometry and examination on the properties of the surrounding soil. The soil is simplified as a homogenous linear viscoelastic material and the dynamic stiffness of the suction caisson is expressed in terms of dimensionless frequency‐dependent coefficients corresponding to different degrees of freedom. The dynamic stiffness coefficients for the skirted foundation are evaluated using a three‐dimensional coupled boundary element/finite element model. Comparisons with known analytical and numerical solutions indicate that the static and dynamic behaviours of the foundation are predicted accurately using the applied model. The analysis has been carried out for different combinations of the skirt length, Poisson's ratio of the subsoil and the ratio of the soil stiffness to the skirt stiffness. Copyright © 2007 John Wiley & Sons, Ltd.     

Dynamic responses of coastal structures during earthquakes including sediment–sea–structure interaction

The effects of the interaction among sea water, sediment, backfill-soil and coastal structures (embankments) were included in the present study. The formulation is derived from fundamental theories in various fields, including marine hydrodynamics, flow in porous medium, and structural dynamics. The hybrid finite-difference and finite element methods were used in the analysis. The finite-difference method was used to calculate the nonlinear hydrodynamic pressures of sea water as well as the pore water in the sediment acting on the coastal embankment faces by seismic-wave actions. The fluid-filled solid mixture was used to model sediment and back-fill soil and the corresponding dynamic responses were also evaluated by finite difference method. The dynamic response of the coastal structures was calculated by finite element method. The numerical results are presented for various water depths and ground motion intensities. The significant dynamic forces on coastal structures were calculated during earthquakes and the possible sliding of the coastal embankment will occur and the special foundation treatment should be made.     

自适应时间步长法在土体冻结水热耦合模型中的应用

由于相变的存在,土体冻结过程中的温度传导与水分迁移是一个复杂的物理过程。为了更好地描述冻结过程中水分与温度的变化规律,通过对不饱和土体水分传导方程的研究,考虑冻结过程中的相变,建立了一维冻土水热耦合模型。给出了相应的差分与有限元程序,并对室内冻结实验进行了模拟。提出误差因子的概念,通过对程序计算中时间步长与计算用时、误差关系的分析,论证了进行时间步长优化的必要性。在两种不同数值方法的对比中,体现了有限元计算的稳定性。提出了调整后的自适应时间步长计算方法。计算结果表明,优化时间步的自适应步长法,在不影响模型计算准确度的前提下,可以大幅减少计算用时,提高计算效率。     

Experimental validation of soil–structure interaction of offshore wind turbines

Estimating the natural frequencies of a wind turbine system consisting rotor, nacelle, tower, foundation and surrounding soil is one of the important design considerations. This paper experimentally investigates the behaviour of a model wind turbine supported on a particular type of foundation called a monopile. Monopile is a single large diameter (2.5–4 m) long slender column inserted deep into the ground. This can be thought of as an extension of the wind turbine tower. In particular, the role of soil/foundation in the dynamics of wind turbines has been investigated. Analytical methods are developed incorporating the rotational and translation flexibility of the foundation. Novel experimental techniques have been developed to obtain the parameters necessary for the analytical model. The analytical model is validated using a finite element approach and experimental measurements. In total, results from 17 test cases is reported in the paper. Experimental results show that the natural frequencies and the damping factors of the wind turbine tower change significantly with the type of soil/foundation. Analytical results for the natural frequencies agree reasonably well to the experimental results and finite element results.     

基坑桩地震冲击下的受力分析模型仿真

当前利用改进动力Winkler模型分析基坑桩地震冲击下的受力情况,不能预防应力波的反射作用,导致其分析结果具有不全面、准确性低的缺点。本论述提出有限元数值模拟的基坑桩地震冲击下的受力分析模型,通过基坑桩小应变模型描述不同应力状态下基坑桩模量的变化,采用有限元数值模拟方法结合基坑桩小应变模型对基坑桩有限元模型进行塑造。在约束基坑桩有限元模型边界条件时,模型选择黏性阻尼器的吸收边界,使模型边界上的应力波不会遭到折射,避免运算结果出现误差。利用Newmark方法对基坑桩有限元模型进行动力时程分析,实现基坑桩在不同应力状态下的受力分析。实验结果证明:所提模型能够有效、准确的对地震冲击下的基坑应力分布、基坑桩身弯曲度、变形位移以及桩体水平位移差值对比等进行全面的分析。