Elastic flexural-torsional buckling of steel beams with rigid and continuous lateral restraints

A simple model of the elastic buckling of steel beams with rigid and continuous lateral restraints has been developed. It is based on a method of displacements that associate lateral restraint conditions. A numerical procedure for resolving the resulting partial differential equations is proposed in which rotations are approximated by trigonometric functions. The effects of moment distribution and continuous restraints on the elastic flexural-torsional buckling of beams are also studied and design approximations and procedures developed. This study also highlights that the restraint of the tensioned part of the beam is not sufficient to limit lateral buckling. The use of these solutions is demonstrated by two examples.     

考虑泥浆触变性和管土接触特性的顶管摩阻力公式

顶进力是顶管工程设计和施工的重要参数,而顶管侧摩阻力对顶进力起控制作用,其大小主要受管土接触和管浆接触特性影响。为了更加准确地计算顶管摩阻力,假设隧洞孔壁在泥浆压力作用下保持稳定,管道周围同时存在管土接触和管浆接触,采用协调表面Persson接触模型分析管土接触特性,得出考虑接触压力分布影响的管土摩阻力;然后利用半无限弹性体中柱形圆孔扩张理论分析注浆压力对泥浆套厚度的影响,并结合泥浆触变性和流体力学平行平板模型计算管浆摩阻力。在此基础上考虑管道与隧洞的相对位置,同时将管道顶进时的滑动摩擦阻力作为下限值,顶管重启动时的静摩擦阻力作为上限值,总结出直线和曲线顶管摩阻力公式。通过与工程实例数据对比,结果表明该计算公式下限值与实测值最接近,证明其适用性。     

基于滑面正应力假设的土压力计算方法

基于滑面正应力假设,提出一种新的极限平衡方法计算挡土结构土压力。首先假定滑裂面上正应力分布为含2个待定参数的三次拉格朗日插值函数;推导出包含主动土压力的水平力、垂直力和绕挡土墙顶点旋转的力矩平衡方程;然后采用优化方法确定最危险滑裂面位置及对应的最大主动土压力。与传统土压力计算方法相比,作者提出的方法可以给出精度较高的土压力分布,且可分析土压力作用点位置对土压力值的影响,其土压力计算方法可应用于工程上。     

一种基于Morgenstern-Price法假定的三维边坡稳定性分析法

 通过侧向剪力系数和侧向剪力分布函数对条间力进行假定,提出所有条柱满足3个力的平衡、滑坡体满足3个力矩平衡的三维边坡极限平衡分析法,可看作是二维Morgenstern-Price法的三维扩展。利用滑体力的平衡条件和边界条件分别得到条柱各行和各列的安全系数,再利用滑体整体力矩平衡条件确定侧向剪力系数?1,?2,?3,?4。该法考虑了所有条间剪力对安全系数的影响,采用直接迭代法求解,提高计算效率。算例分析表明,对于对称边坡,侧向剪力系数?1,?3,?4对安全系数影响不大;对于非对称边坡,?4对安全系数影响也不大,且获得的安全系数均与已有文献结果接近。非对称复合滑动面算例还表明,简化方法给出的安全系数不一定偏于安全。     

L型挡土墙主动土压力计算的基底摩擦系数折减有限元法

提出了通过将基底摩擦系数进行折减,按与传统刚塑性体极限平衡理论相对应的变形体极限平衡理论,采用有限元接触模拟算法进行L型挡土墙主动土压力计算的方法。按照该方法,利用著名非线性有限元分析软件ABAQUS进行了实例计算,以数值模拟手段揭示了坦墙后第二滑裂面的存在,证实了理论上的假设。真实揭示了符合坦墙条件的L型挡土墙后填土中第一和第二滑裂面的位置,且揭示对不严格符合坦墙条件的L型挡土墙,其填土中可能出现第三滑裂面。该方法具有理论上的严密性,而且算例计算比较表明,可更为准确合理地计算出L型挡土墙立板上主动土压力的分布形式及大小,较朗肯土压力理论更加可靠,现行朗肯理论计算的抗滑移稳定安全系数偏于保守,而抗倾覆稳定安全系数偏于危险。同时,该方法计算效率较高,因而具有良好的应用前景。     

Earth pressure coefficients for design of geosynthetic reinforced soil structures

There are several methods proposed in the last two decades that can be used to design geosynthetic reinforced soil retaining walls and slopes. The majority of them are based on limit equilibrium considerations, assuming bi-linear or logarithmic spiral failure surfaces. Based on these failure mechanisms, design charts have been presented by several authors. However, the use of design charts is less and less frequent. The paper presents results from a computer program, based on limit equilibrium analyses, able to quantify earth pressure coefficients for the internal design of geosynthetic reinforced soil structures under static and seismic loading conditions. Failure mechanisms are briefly presented. Earth pressure coefficients calculated by the developed program are compared with values published in the bibliography. The effect of seismic loading on the reinforcement required force is also presented. To avoid the use of design charts and based on the obtained results, approximate equations for earth pressure coefficients estimation are proposed. The performed analyses show that the failure mechanism and the assumptions made have influence on the reinforcement required strength. The increase of reinforcement required strength induced by the seismic loading, when compared to the required strength in static conditions, grows with the backfill internal friction angle. The effects of the vertical component of seismic loading are not very significant.     

单元集成法及其在土压力计算中的应用

基于塑性力学上限定理的土压力计算，在数值上可以通过单元集成法来实现。它采用类似于有限元网格划分的方式离散墙背土体，并设定一个机动许可的滑动机构。在此滑动模式下，可以求得每个单元贡献的外力功率和内能耗散率。所有单元的能量变化率的总和就是墙背土滑裂体的总能量变化率。然后，根据上限定理可以求得与滑动机构相对应的极限外载荷，并通过非线性数学规划法找到其最小值。采用平面和对数螺旋滑裂面的单滑块机制，对典型的二维土压力问题进行分析，其结果说明该方法的有效性。     

非均质地基上浅基础的极限承载力

本文根据塑性极限平衡原理,考虑地基土性的成层分布及粘结力沿深度的非均匀变化,结合变分法,推导了用于确定成层非均质地基极限承载力的基本公式,并采用拟牛顿算法进行了数值求解;基于大量计算结果,分析了土壤强度及其分布、基础埋深、地震荷载及地下水位深度等各种参数及其组合对地基承载力的影响,并将计算结果与已有的解答进行了比较。最后,对非均质地基承载力的表示方法进行了初步探讨。     

Stress-deformed state of cylindrical specimens during indirect tensile strength testing

In this study, the interaction between cylindrical specimen made of homogeneous, isotropic, and linearly elastic material and loading jaws of any curvature is considered in the Brazilian test. It is assumed that the specimen is diametrically compressed by elliptic normal contact stresses. The frictional contact stresses between the specimen and platens are neglected. The analytical solution starts from the contact problem of the loading jaws of any curvature and cylindrical specimen. The contact width, corresponding loading angle(2q0), and elliptical stresses obtained through solution of the contact problems are used as boundary conditions for a cylindrical specimen. The problem of the theory of elasticity for a cylinder is solved using Muskhelishvili's method. In this method, the displacements and stresses are represented in terms of two analytical functions of a complex variable. In the main approaches, the nonlinear interaction between the loading bearing blocks and the specimen as well as the curvature of their surfaces and the elastic parameters of their materials are taken into account. Numerical examples are solved using MATLAB to demonstrate the influence of deformability, curvature of the specimen and platens on the distribution of the normal contact stresses as well as on the tensile and compressive stresses acting across the loaded diameter. Derived equations also allow calculating the modulus of elasticity, total deformation modulus and creep parameters of the specimen material based on the experimental data of radial contraction of the specimen.     

考虑曲线滑裂面的非极限被动土压力计算

传统的土压力计算方法所求结果实际为极限状态土压力值,在工程设计中采用该值可能导致浪费或是产生偏于不安全的后果。而目前对于非极限状态下土压力计算的研究主要假定直线破裂面并针对填土为松散的干砂这一特定情况。鉴于此,考虑不同密实度砂土摩擦角与位移的关系,建立滑裂面为曲面情况下土压力的逐层计算方法,推导非极限状态下被动土压力强度、合力及其作用点的计算公式。分别验算填土为不同密实程度砂土以及饱和砂土的模型试验,与实测数据对比,发现两者结论比较吻合。     

实腹式型钢混凝土梁正截面承载力下限

实腹式型钢混凝土梁中型钢和混凝土之间的滑移会引起梁正截面承载力的变化,本文阐述了取得这一变化下限的条件和计算此下限值的方法。这一方法为评估粘结退化的型钢混凝土梁的承载力提供了科学的依据。首先,从梁中型钢和钢筋混凝土之间有滑移时的协调变形问题出发,提出复合平截面假定,讨论了取得梁正截面承载力下限的条件,建立了求解此下限值的截面平衡方程组,并将其数值解与试验结果进行对比,发现二者符合比较好,并给出相应的简化计算方法用于工程设计实践。     

吊车梁的轮压荷载支承长度计算

吊车轮压荷载沿吊车梁跨度方向的支承长度就是吊车车轮与轨道的接触面宽度 ,吊车车轮与轨道的接触问题更接近平面应力问题。采用平面应力弹性理论 ,对吊车车轮与轨道的接触区尺寸进行理论分析。取在压力荷载作用下沿母线接触的两有限长度钢圆柱作为分析模型 ,得出了车轮与轨道的接触区宽度的计算公式。在 5 0 0 0kN长柱试验机上进行了轮子与轨道的接触问题试验 ,接触区尺寸采用印痕法测量。接触区宽度的试验值与理论计算值非常接近 ,可见分析接触问题的方法是合理的。得出的计算公式可供设计时参考。     

Temperature prediction for contour-insulated concrete-filled CHS subjected to fire using large time Green’s function solutions

An accurate numerical approach is developed in this paper for thermal analysis of contour-insulated concrete-filled circular hollow sections subjected to fire, based on analytical solutions of transient diffusion equations in radial coordinate system obtained using the Green’s function approach. The steel layer is conveniently treated as a thin film with lumped heat capacitance, i.e. the temperature distribution inside the steel section is assumed to be uniform. Perfect contact conditions are assumed at both of the insulation-steel and the steel-concrete interfaces. Solutions of the heat equations are represented by large time series expansions obtained from homogeneous boundary conditions using the eigenfunction approach. The time-varying boundary conditions, i.e. the fire conditions are incorporated in terms of Stieltjes integral by means of Duhamel’s theorem. Numerical models are developed using temporal discretization, while no spatial discretization is required since spatial variables are analytically tractable. The proposed numerical scheme is not restricted to any specific fire conditions, and can be used in conjunction with parametric fire as proposed in the Eurocode.     

基于颗粒椭球体理论的隧道松动土压力计算方法

基于颗粒椭球体理论认为隧道上部松动区滑动面为椭圆形,据此推导出受滑动面倾角影响的侧土压力系数计算方法;在椭圆形松动区内竖向荷载沿水平向呈梯形分布,推导出隧道松动土压力计算方法。结果表明:当埋深低于极限椭圆高度时,松动区域为地面线以下的极限椭圆区域;当埋深达到极限椭圆高度时,松动区为整个极限椭圆,松动土压力不再增加。滑动面侧土压力系数是变化的,与滑动面倾角和土的摩擦角有关,随着内摩擦角增大而减小,随着滑动面倾角增大而增大。取值范围为0.2~0.8,介于主动土压力系数和Krynine侧土压力系数之间。本模型计算结果与实测数据较为吻合,可以用于隧道设计和施工中。     

基于数值应力场的极限平衡法及其工程应用

 数值分析可较准确地计算岩土体应力分布,但求解安全系数存在诸多困难;极限平衡法计算安全系数概念明确、过程简单,但假设过多,精度又受到限制。利用数值分析得到的应力场,计算潜在滑动面上正应力分布,再按滑面正应力修正的方法求解出满足所有平衡条件的安全系数。这种基于数值应力场的极限平衡方法充分利用数值方法与极限平衡法的优点,得到理论上更合理的安全系数。将这种新的极限平衡方法应用于武都水库坝基的深层抗滑稳定性分析,并与传统的极限平衡法及有限元强度折减法进行比较,计算结果满意,并被坝基加固设计所采纳。     

北京国际饭店蝶形箱基地基反力实验研究

荣获北京８０年代十大建筑之一的北京国际饭店，其天然地基蝶形箱基的设计超出了箱基设计与施工规程（ＪＧＪ６－８０）的范围，为了获得设计依据进行了室内模型试验，随后又进行了工程现场实测。本文重点介绍基础工程和土力学主要课题之一的地基反力分布性状实验结果，供设计和研究人员参考。     

多水源给水管网的技术经济计算

联立管网节点经济水压方程组并引入节点水压边界条件，建立包含起点水压已给和未给两种情况的多水源给水管网技术经济计算的数学模型。采用牛顿迭代法来求解各未知节点的经济水压，进而得出各管段的经济水头损失、经济管径和水源二级泵站的经济扬程。最后再将理论管径圆整为标准管径，并重新核算管网实际水力工况；据此编写了通用电算程序，经多水源给水管网实例验证，可快捷准确地进行技术经济计算，得出较满意的结果。     

The Thiel–Zsutty earthquake damage model,reformulated and extended

The Thiel–Zsutty (TZ) model predicts mean and the probability distribution function for earthquake damageability of building as a function of peak ground acceleration. ATC‐13‐1 provides an alternate damageability model based on modified Mercalli intensity characterization of ground motion and a beta distribution function for selected building types. This paper provides a reconciliation of the TZ and Applied Technology Council (ATC) methods. It is shown that the beta distribution can provide a continuous representation of the step‐wise TZ Markov distribution function. When the TZ model uses a compression factor for the standard deviation to represent the degree of uncertainty in the parameters, then the TZ results are found to be consistent with the ATC‐13‐1 distribution function for a specific compression factor of 0.40. This paper provides a new, simply applicable method to determine the damage distribution function for a given site, building type, and site conditions; using a beta distribution and allowing inclusion of the degree of confidence the assessor has in the determination of the parameters. New equations are provided to estimate the mean, standard deviation, and upper confidence limit of the damage ratio.     

基于条分法理念的土压力计算

将库仑土压力假定与条分法相结合,采用与滑裂面相平行的微条对滑动楔体进行划分,并对微条进行受力分析,建立了平衡方程,推导了主、被动土压力计算公式。分析表明:土压力沿墙高线性分布,土压力大小与库仑理论的计算结果一致。     

三维边坡严格与准严格极限平衡解答及工程应用

分别推导出满足所有6个平衡条件三维边坡严格极限平衡解答和满足5个平衡条件的三维边坡准严格极限平衡解答。假定空间滑面上正应力初始分布,对于严格解,用含5个参数的修正函数对其修正;对于准严格解,则采用含4个参数的修正函数。严格平衡方程组最终化为关于三维安全系数的六次代数方程,通过调节滑动方向和转动系数使修正后滑面正应力为正,从而得到有意义的严格极限平衡解答;而准严格平衡方程组最终化为关于三维安全系数的四次代数方程,其最大解析实根为准严格极限平衡解答,且只需调节滑动方向,计算过程更为方便实用。算例计算结果表明,三维边坡准严格解答与严格解答十分接近,对工程问题可直接采用准严格解答。该方法计算原理简单,易于编程实施,计算结果精度高,且适合任意形状空间滑面。应用该方法对重庆乌江银盘水电站左岸坝肩边坡及坝基岩体进行三维稳定性分析,克服了二维稳定性分析的局限性,计算结果更为合理可靠,为坝基与坝肩加固设计提供理论依据。