弹性地基中厚板弯曲问题的无网格LRPIM分析

无网格局部径向点插值方法（LRPIM）的形状函数具有Kronecker delta函数的特性,便于施加位移边界条件,不需要进行特殊地处理。采用局部加权残值法推导了双参数弹性地基中厚板的离散系统方程,利用无网格LRPIM对四边简支和四边固支以及筏式双参数弹性地基中厚板的弯曲问题进行了分析和计算。算例表明,用无网格LRPIM分析弹性地基中厚板问题具有非常灵活和易于实现等优点。     

弹性地基上水工结构各向异性Mindlin底板计算分析的无单元法（EFGM）

无单元法（element free galerkin method）是一种基于滑动最小二乘法构造插值函数的无网格数值方法。以该方法中插值函数及其导函数为基础,从变分原理出发,建立了弹性地基上正交各向异性Mindlin板的无单元法求解控制方程,其中弹性地基采用Winkler地基模型。对该理论方法进行了相应的程序实现,最后通过算例分析表明了提出方法用于水工结构中弹性地基板问题分析的可行性和有效性。     

移动荷载作用下Winkler地基板的等参元分析

采用基于Mindlin板理论的8节点等参单元和Newmark逐步积分法,对Winkler地基上的弹性薄板和厚板在移动荷载作用下的动力响应进行了分析,并与已有的薄板有限条法分析结果进行了对比。考察了荷载移动速度、地基基床系数、系统阻尼比对地基板动力响应的影响。分析结果表明,系统存在固有的共振速度,地基基床系数是确定共振速度的最重要因素,薄板与厚板的挠度响应模态有很大差异。结果证明了该方法的有效性和准确性,对实际工程有重要的应用价值。     

A quasistatic analysis of a plate on consolidating layered soils by analytical layer‐element/finite element method coupling

In this paper, a coupling method between finite element and analytical layer‐elements is utilized to analyze the time‐dependent behavior of a plate of any shape and finite rigidity resting on layered saturated soils. Based on the integral transform techniques together with the aid of an order reduction method, an analytical layer‐element solution is derived from the governing equations for three‐dimensional Biot consolidation with respect to a Cartesian coordinate system and then extended to be the fundamental solution for the layered saturated soil under a point load. The Mindlin plate is modeled by eight‐noded isoparametric elements. The governing equations of the interaction between soil and plate in the Laplace‐Fourier transformed domain are deduced by referring to the coupling theory of FEM/BEM, and the final solution is obtained by applying numerical inversion. Numerical examples concerned with the time‐dependent response of a plate are performed to demonstrate the influence of soil and plate properties on the interaction process. Copyright © 2014 John Wiley & Sons, Ltd.     

双参数地基上弹性板的动力分析

采用双参数地基模型和基于Mindlin板理论的8节点等参单元,根据Hamilton变分原理,推导了弹性地基上弹性板动力分析的有限元公式,将地基效应和板面质量分布归并到板的刚度矩阵和质量矩阵中,采用边界元法考虑板域外地基变形的影响。分析了四边自由矩形板的自由振动和强迫振动,计算的自由振动固有频率与实测结果相近,发生共振时板的强迫振动动力响应达到峰值,在给定的阻尼比条件下,无阻尼的稳态响应与有阻尼的稳态响应趋于相同,阻尼能够显著降低板的共振响应。     

Finite element analysis of reinforced embankment foundation

A finite element analysis of a reinforced embankment-foundation system has been conducted using a coupled formulation and elastoplasticity theory. Such important factors as type of reinforcement, the type of clay, depth of foundation and drainage condition affecting the system have been systematically investigated using appropriate constitutive models to depict various components of the system and material parameters of two typical soft clay deposits found in India. The displacements, reinforcement force and maximum heights of the embankments are among the aspects presented and discussed. It is shown that the effectiveness of the reinforcement is dependent on its stiffness and the shear strength of the clay deposit. The foundation depth has significant effect on the nature and magnitude of displacement, the reinforcement force and the height of embankment. Drainage conditions are shown to markedly influence the effectiveness of reinforcement. Copyright © 1999 John Wiley & Sons, Ltd.     

Numerical stability for modelling of dynamic two‐phase interaction

Dynamic two‐phase interaction of soil can be modelled by a displacement‐based, two‐phase formulation. The finite element method together with a semi‐implicit Euler–Cromer time‐stepping scheme renders a discrete equation that can be solved by recursion. By experience, it is found that the CFL stability condition for undrained wave propagation is not sufficient for the considered two‐phase formulation to be numerically stable at low values of permeability. Because the stability analysis of the two‐phase formulation is onerous, an analysis is performed on a simplified two‐phase formulation that is derived by assuming an incompressible pore fluid. The deformation of saturated porous media is now captured in a single, second‐order partial differential equation, where the energy dissipation associated with the flow of the fluid relative to the soil skeleton is represented by a damping term. The paper focuses on the different options to discretize the damping term and its effect on the stability criterion. Based on the eigenvalue analyses of a single element, it is observed that in addition to the CFL stability condition, the influence of the permeability must be included. This paper introduces a permeability‐dependent stability criterion. The findings are illustrated and validated with an example for the dynamic response of a sand deposit. Copyright © 2015 John Wiley & Sons, Ltd.     

风机基础结构有限元分析

本文利用ANSYS软件建立风机基础的有限元模型,将数值计算结果与常规设计进行对比,发现风机基础结构设计中可能存在的问题。研究金属环和基础截面尺寸对结构受力的影响,分析变形、应力分布、荷载分配、裂缝规律,并提出设计建议。     

粉喷桩单桩复合地基承载特性的有限元分析

采用有限元法对粉喷桩单桩复合地基的承载特性进行数值试验。.分析了在整个加荷过程中单桩荷载传递特性和该复合地基的桩土应力比的变化规律,同时分析了褥垫层厚度及其变形模量对桩土应力比的影响。     

混凝土开裂对地基板弯矩的影响

当前地基板的配筋设计均按弹性体计算得到的弯矩进行，这在理论上是不合理的，因为地基板是高次超静定问题，地基板开裂后其弯矩会有较大的改变。笔者通过合理模拟地基板裂缝开展过程及土．结构的相互作用，采用非线性有限单元法对地基板进行了分析，着重讨论了不同计算方法及裂缝对地基板弯矩的影响。计算结果表明，按平面问题计算得到的弯矩比按空间问题大40％左右，地基板开裂后弯矩减小，且裂缝越多，弯矩减小越多。     

刚柔复合桩基性状的有限元分析

通过建立的6×6桩刚柔桩基模型,对复合桩基协同工作性状进行了三维有限元分析。研究了在不同刚、柔性桩数比例与不同荷载水平下桩顶荷载、地基中应力与应变的变化规律。如果刚、柔性桩数比例不变、桩承受荷载小于其承载力极限值,则在不同荷载水平下刚、柔性桩顶所受荷载比值基本不变;同一荷载水平下存在刚性桩数与总桩数的一个经济比例（不大于40 %）,当刚性桩数与总桩数比小于该比例时,增加刚性桩数量能有效减少浅层土中的应力,减沉效果明显;当刚、柔性桩数比例大于该比例时,增加刚性桩数量,地基中应力与应变减少效果不显著。     

Finite element analyses of layered visco‐elastic system under vertical circular loading

Analyses for the response of a linear visco‐elastic system subjected to axi‐symmetric vertical circular loading are presented. Hankel transforms with respect to the radial spatial coordinate are used to reduce the three‐dimensional problem to that involving only a single spatial dimension, which is then discretized using the finite element method. Three techniques are employed to handle the time factor in the visco‐elastic material: (i) direct time integration; (ii) Fourier transforms; and (iii) Laplace transforms. These methods are compared and evaluated through their numerical results. Copyright © 2007 John Wiley & Sons, Ltd.     

深基坑开挖的有限元模拟与实验研究

本文根据Goodman接触面单元和Duncan-Chang模型编制了二维有限元程序SJK。考虑了工程实际中分步开挖、支撑等一系列施工过程,利用模型试验对该程序进行了验证,实测结果与理论计算值两者较为接近,为工程设计和施工提供参考     

基坑悬臂支护桩双参数弹性地基杆系有限元法

对地基抗力双参数法在基坑悬臂支护桩位移和内力计算方面进行了探讨,即采用地基土抗力系数随深度按双参数非线性变化的假设,以弹性地基杆系单元模拟,支护桩则按弹性梁单元模拟。对某基坑悬臂支护桩进行数值模拟反分析表明,通过试算调整可获得适合于实际设计计算的地基抗力双参数,该法应用到福州市某基坑悬臂桩的实际分析和设计中获得了较为满意的结果,可供悬臂支护桩设计计算时参考。     

止水帷幕对基坑环境效应影响的有限元分析

采用Biot固结理论分析了止水帷幕对基坑工程环境效应的影响,包括止水帷幕不同打设深度的效果,以及两种封闭式止水帷幕发生漏水意外时对地下水位和坑外土体位移的影响等。在有限元编程中,将开挖土体置为空气单元可以简化处理过程。算例分析结果表明,深厚透水地基中增加竖向止水帷幕的深度并不能有效减小对周围环境的影响;漏水部位周围土体的渗流等势线较为密集,渗流速度较大,容易诱发扩大破坏;竖向封闭式止水帷幕漏水引起的坑边土体的沉降和地表土体的侧移相对较大,水位下降迅速等。其结果可供基坑工程漏水事故环境效应的评价和对策研究时参考。     

柔性基础复合地基力学性状的有限元分析

通过有限元分析方法,考虑复合地基中各种材料的非线性特性,对柔性基础下复合地基的力学性状作了初步的数值模拟分析,找出了柔性基础复合地基桩土间的荷载分担、荷载沿深度变化和传递、桩土间相互作用、变形特性等力学性状的一些基本规律。     

无拉力双地基参数板在移动荷载作用下的动力响应

求解了无拉力双参数地基上厚、薄板受任意移动荷载作用下的动力响应问题和板的脱离问题。从板-地基接触系统的分区广义势能泛函出发,通过建立和分析板单元区、地基单元区和连接板-地基的接触单元区的势能泛函,给出求解无拉力双参数地基板受任意移动荷载作用下的动力响应问题的分区广义协调元法。利用纽马克（Newmark）法经MATLAB编程叠代数值计算,验证了文中方法分析无拉力双参数地基板的动力响应问题是有效的。     

刚-柔性桩复合地基变形特性有限元分析

在现场试验基础上对条形基础下刚-柔性桩复合地基进行有限元模拟分析。着重讨论了褥垫层、承台、刚性桩、柔性桩等的参数变化对刚-柔性桩复合地基沉降特性的影响。结果表明,复合地基沉降随着褥垫层厚度减小而减小,随着褥垫层模量增加而减小,承台厚度增加有利于减少差异沉降,刚性桩是控制沉降的主要构件,柔性桩桩长增加可以减少差异沉降。分析结果为刚-柔性桩复合地基的优化设计提供理论基础。     

小湾拱坝坝基开挖卸荷松弛效应的有限元分析

针对小湾拱坝坝基开挖中出现的卸荷松弛问题,采用三维非线性有限元法对卸荷松弛效应进行了评价。通过松弛方案与未松弛方案计算,对小湾拱坝的应力和位移、屈服区分布以及坝基浅部关键截面的抗剪安全度、点安全度等方面进行了比较分析。研究结果表明,建基面地基松弛后,主要影响低高程局部区域的变形和应力,对拱坝整体变形和应力分布的影响很小;地基松弛后,拱冠梁建基面（953 m高程）坝踵处第一主应力有所增大,坝趾处第三主应力有所减小;拱冠处梁的作用减弱,拱冠梁处距坝踵20 m范围的点安全系数也略有降低;原设计方案在未松弛情况下基本可以满足《混凝土拱坝设计规范》关于建基面抗剪（断）安全系数的要求;坝基松弛后,抗剪（断）安全系数降低明显,与规范规定的要求相差较大,需采取适当的工程措施。该研究成果已为设计决策提供了依据。