用机动法作连续梁内力影响线的问题与建议

指出了当前连续梁内力影响线的求解方法中存在的问题，给出了解决问题的建议。     

机动法作影响线与反力-位移互等定理

根据反力-位移互等定理直接导出了影响线的机动作法,并给出了一种概念更为直接明了的计算和绘制超静定力影响线的方法.     

基于虚位移原理的直接机动法作超静定力影响线

当前教材中介绍的作超静定力影响线的机动法是一种联合使用力法和位移互等定理的间接方法,与作静定力影响线的机动法不一致. 本文建立了求作超静定结构反力和内力影响线的直接机动法. 首先利用虚位移原理推导了机动法求作超静定结构内力(反力) 影响线的公式,表明超静定结构影响线对应于撤除了相应约束的基本结构施加单位位移引起的位移曲线. 然后给出了一种概念清晰、过程统一、适用广泛的计算超静定力影响线方程的方法,最后展示了几个具体算例.     

一种求解静定组合结构与桁架结构影响线的简便算法1)

基于静定组合结构和桁架结构体系复杂性以及计算影响线步骤繁琐性的问题,本文通过虚位移互等原理,把静定组合结构与桁架结构化简为简支梁,将复杂结构转化为简单结构,把求轴力影响线转化为求简支梁弯矩与剪力影响线进行计算。结果表明：此方法计算步骤简单且易于掌握,有利于简化计算,可用于结构力学教学的补充,也可为工程设计人员借鉴参考。     

超静定型钢桁架优化设计的面积比法

满应力准则是对超静定型钢桁架进行优化设计的有效方法．但这种方法的主要缺点在于收敛速度很慢甚至不收敛,这给设计工作带来很大的不便．对问题进行了研究,在“型钢压杆稳定设计直接法”的基础上,提出了满应力优化设计的一种新方法——面积比法,有效地提高了设计过程的收敛速度,降低了设计成本,供有关结构设计人员参考．     

桁架内力计算方法的讨论

在现有结构力学教材中,桁架内力的计算方法大体上可以分为：结点法、截面法及根据几何分析采取的某种方法,但是根据几何分析而采取某种方法的讨论较少. 本文作者根据多年教学经验,提出了桁架可根据几何构造特点而采取适当的方法——简支梁法及三铰刚架法,另外对结点法也进行了进一步的讨论.     

数值模型内力影响面分析的机动法

本文提出并证明了普遍适用于以广义位移为独立变量的各种数值模型的内力影响面分析的机动算法原理。这一原理把内力影响面分析归结为求解在一个等价荷载作用下的结构位移场,并给出了得到等价荷载的方法。用本文方法得到的是结构某一点的内力的影响面,而且对数值模型来说,是精确解。作为本文原理的应用,用机动法分析了采用有限条模型的薄板的内力影响面,并给出了若干数值例子。     

静定平面桁架设计性实验教学模型的研制

本静定平面桁架设计性实验教学模型为学生提供可自行组装的桁架结构,结合理论计算与电测实验技术,研究实际桁架与理想桁架杆件的受力情况. 实验结果表明,本静定平面桁架模型的设计是比较理想的. 通过该模型的设计,可以培养学生独立设计实验、发现问题和解决问题的能力以及掌握相关的实验操作技能等;使学生充分认识实际桁架与理想桁架构造上的差别,是《理论力学》和《结构力学》等课程教学的有效补充与延伸.     

求超静定结构精确影响线方程的简捷方法

本文提供了一种确定超静定结构精确影响线方程的方法,而且用的数学手段非常简单,无论是在结构力学教学中还是在有关的工程实际中都是一种值得提倡的方法.     

具有随机拉索刚度的预应力钢桁架随机内力摄动分析

本文在建立拉索式预应力钢桁架基本计算理论的基础上，考虑到拉索刚度的随机性，推导了拉索式平面预应力钢桁架随机内力摄动分析的一般公式及敏度分析式，并给出了算例。为进一步进行预应力钢桁架可靠性分析奠定了基础。     

A method of adjusting bar-length of statically indeterminate truss for increasing its load capacity

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随机拉索刚度预应力空间钢桁架随机内力摄动分析

基于已建立的拉索式平面预应力钢桁架基本理论 ,考虑到拉索刚度的随机性 ,得到了拉索式空间预应力钢桁架随机内力摄动分析的一般公式及敏度分析式 ,给出了空间预应力钢桁架随机内力统计特性计算表达式。为进一步进行空间预应力钢桁架可靠性分析奠定了一定的理论基础。最后针对工程中常见的三角形立体钢桁架 ,给出了算例     

Sizing optimization of truss structures by method of centers and force formulation

This paper describes a new approach to optimum weight design of truss structures. The force method is incorporated in an optimization algorithm based on the method of center points. Design variables are the member cross-sectional areas and the redundant forces evaluated for each independent loading condition acting on the structure. The optimization method utilizes the largest hyperspheres inscribed within the feasible space. The method of hyperspheres has been enhanced here to handle the compatibility equality constraints as well. By including the analysis step in the optimization cycle there is no longer the need to perform separate structural analyses thus saving computation time. The viability and efficiency of the proposed method are demonstrated for truss structures subject to multiple loading conditions and constraints on member stresses, nodal displacement and minimum gage. Numerical results are compared with those reported in the literature.     

The equations of Reissner-Mindlin plates obtained by the method of internal constraints

The aim of this paper is to give the title theory of shearable plates a precise and exact position with respect to three-dimensional linear elasticity. We assume that the Reissner-Mindlin representation of the displacement field hold in a 3-D body in the shape of a plate, and discuss how a constitutive response consistent with such a representation should be chosen. We find that the Reissner-Mindlin plate theory results from mere integration over the thickness of the equilibrium equations of a cylindrical body made of a linearly elastic material which is both transversely inextensible and transversely isotropic.

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Sommario Scopo di questo articolo è fornire una deduzione esatta, nell'ambito dell'elasticità lineare tridimensionale, della teoria delle piastre deformabili a taglio menzionata nel titolo. Ammesso che la rappresentazione di Reissner-Mindlin per il campo di spostamento valga in una regione tridimensionale a forma di piastra, si discute come scegliere la risposta costitutiva in maniera coerente con quella rappresentazione. Si trova che la teoria delle piastre di Reissner-Mindlin si ottiene per semplice integrazione sullo spessore delle equazioni di equilibrio di un corpo cilindrico che sia costituito di un materiale linearmente elastico tanto trasversalmente inestensibile che trasversalmente isotropo.

     

The nominal force method for truss geometry and topology optimization incorporating stability considerations

This paper presents a computationally efficient method for truss layout optimization with stability constraints. Previously proposed approaches that ensure stability of optimal frameworks are first reviewed, showing that existing studies are generally restricted to topology optimization. The present contribution aims to generalize the approach to simultaneous geometry and topology optimization. A lower-bound plastic design formulation under multiple loading will serve as basis for this purpose. The numerical difficulties associated with geometrical variations are identified and the parametrization is adapted accordingly. To avoid nodal instability, the nominal force method is adopted, which introduces artificial loading cases to simulate the effect of geometric imperfections. Hence, the truss systems with unstable nodes are eliminated from the set of optimal solutions. At the same time, the local stability of structural members is ensured via a consistent local buckling criterion. This novel formulation leads to optimal configurations that can be practically used for the preliminary design of structural frameworks. Four applications illustrate the impact of stability constraints on the solution. The importance of geometry optimization is also pointed out by comparing with results that would be unattainable by topology optimization only.     

超静定梁变形计算的积分法

从线性化弯矩和曲率关系出发,将超静定梁多余反力的弯矩叠加到梁截面弯 矩中去,经两次积分得到了包括积分常数和多余反力的分段转角方程和挠曲线方程,利用边界 条件和连续条件确定积分常数和多余反力,进而确定了转角方程和挠曲线方程.文中工作扩大 了积分法的应用范围. 教学实践表明,用积分法解超静定梁的变形能够起到帮助学生学习和 掌握固体力学的边值问题解题思想的作用.     

The influence of kinematic waves on jet break down

The breakdown of a liquid jet is commonly considered as an effect of the surface tension. However, essential aspects of the boundary wave amplification and the final disintegration of velocity modulated jets can be explained by non-linear travelling time effects, which are of purely kinematic nature. The experiments are carried out on jets with radii between 1.2 to 2.5 mm and Weber numbers between 17 to 200. The experimental results are compared with a theoretical solution which neglects the surface tension.