基于多目标等效风荷载的变截面门式刚架抗风优化

轻钢门式刚架结构是单层工业厂房中一种常见的结构形式,风荷载是其结构设计的重要荷载之一.已有抗风优化研究中一般仅考虑单目标的等效静力风荷载,在多个约束条件时不能保证优化结果的准确性.笔者基于风洞试验数据库构造多目标等效静力风荷载,基于最优准则法对单榀变截面门式刚架进行抗风优化设计.分别以工字钢的腹板高度和材料总重为设计变量和优化目标,以柱顶水平位移和跨中挠度为约束条件,基于MATLAB数值平台,编制了抗风优化计算程序.研究表明,多目标等效静力风荷载能够保证约束位移的数值与随机峰值基本一致,在满足约束条件的前提下,优化设计使结构总重降低了23.2%,经济效益明显,且优化后的截面尺寸符合变截面门式刚架的力学特点.

荷载工况多目标下钢筋混凝土深梁的拓扑拉压杆模型设计

为了提高钢筋混凝土深梁构件配筋设计方法的合理性,选用遗传演化结构优化算法,并延伸出荷载工况多目标下的应用方式,同时基于拓扑解构建拉压杆模型,衔接拓扑优化与工程设计环节,建立荷载工况多目标拓扑拉压杆模型。采用两个深梁数值算例验证了该模型的可行性和稳定性。从建立拉压杆模型的角度以其力学特性出发,将荷载工况多目标优化的拓扑解分别与各荷载工况单目标优化解、其弹性叠加结果,以及所有荷载工况共同作用下的单目标优化解进行比较,证实了新模型更契合深梁类构件的受力特性,具有更佳的全局寻优能力。荷载工况多目标遗传演化结构优化可以有效解决多目标优化中的病态荷载问题,依据其建立的拉压杆模型直观可行,可以为钢筋混凝土深梁设计提供参考。

基于约束加权最小二乘的多目标等效静力风荷载方法在大跨屋盖中的应用

为计算大跨屋盖多目标等效静力风荷载,采用约束加权最小二乘方法,设基本向量为完全三分量单目标等效静力风荷载,推导了一种完全三分量多目标等效静力风荷载方法。以一个开孔屋盖为例,进行了刚性模型测压风洞试验,研究了该屋盖的单目标和多目标等效静力风荷载。结果表明:单目标和多目标等效静力风荷载的分布形状相似,多目标等效结果大于单目标等效结果;采用单目标等效静力风荷载方法,精确等效节点的等效位移与实际位移完全相等,但其它等效节点的等效位移明显偏离实际位移,最大误差可达72.1%;而完全三分量多目标等效静力风荷载方法下的其它等效节点的等效位移与实际位移相差较小,最大误差仅为6.1%,适合大跨屋盖等效静力风荷载的多目标等效。

大跨屋盖结构多目标等效静风荷载分析方法

针对大跨屋盖结构多振型参与风振的特点,提出一种多目标等效静风荷载确定方法。其基本思想是,分别建立多目标等效方程组和约束方程组,前者可获得与各等效目标吻合程度最好的解,后者是根据风荷载作用方向为垂直于建筑物表面的钝体空气动力学原理得到的风荷载各方向分量的关系,限制某些奇异荷载作用模式的出现,从而解决了大跨屋盖结构等效静风荷载研究中突出存在的多目标等效问题。结合两个典型大跨屋盖结构的风洞试验,对不同类型的结构响应进行了等效静风荷载分析,并将分析结果与采用单目标方法所得的结果进行对比,结果表明该方法得到的等效静风荷载作用下各类响应均与动力极值响应吻合良好,达到了以少量的等效静风荷载模式实现所有目标等效的目的,并且所得等效静风荷载分布较符合实际风荷载作用规律。

超龄服役桥梁实际承载能力评定方法探讨

建国以来,我国公路桥梁的设计荷载标准达37种之多,但评定不同时期桥梁承载能力应满足现行荷载通行的要求,否则应核定其目标荷载(限载);而评定桥梁承载能力有基本组合检算法和静载试验核定法,通过承载能力检算和静载试验验证相结合的方法核定桥梁的实际承载能力,阐明了对于确定桥梁目标荷载(限载)来讲,采用验算法即能评定桥梁实际承载力,为类似桥梁的适应性评定提供了借鉴。

大型冷却塔结构多目标等效静风荷载分析

大型冷却塔属于典型的风敏感结构,针对其风振响应的多耦合效应、多振型参与和多目标等效的特点,以冷却塔表面平均风荷载和主导振型的惯性风荷载作为构造多目标等效静风荷载的2个基本向量,并结合约束最小二乘法,得到基本向量的最优组合系数,从而获得针对多个等效目标的等效静风荷载。该方法的优点是:建立了更符合实际分布的等效风荷载,限制了某些奇异荷载作用模式的出现,能够再现风振响应特点。结合某核电站大型冷却塔结构的风洞试验,对3组不同等效目标的结构响应进行了多目标等效静风荷载分析,结果表明在该方法得到的多目标等效静力风荷载作用下的风振响应与极值响应吻合较好。

大跨度桥梁位移响应多目标等效静力风荷载计算方法

为把风荷载作用下的复杂结构动力计算转化为静力计算,根据大跨度桥梁结构的自身特点,以结构非约束节点的位移响应为等效目标,基于随机振动理论和结构动力学基本原理,采用耦合抖振分析方法,分别将竖向、水平和扭转方向的位移等效静力风荷载表达为结构振型矩阵、位移响应影响线矩阵、气动频响传递函数矩阵、抖振力功率谱密度矩阵和峰值因子的乘积。结果表明:根据荷载-响应之间的关系,采用该方法计算得到的等效静力风荷载为基于结构位移响应的大跨度桥梁多目标等效静力风荷载,且具有明确的物理意义;以主跨300m的理想薄平板断面简支梁桥为例,验证了该方法的正确性和有效性。

Multi-objective optimization of multi-cell conical structures under dynamic loads

In this paper,crashworthiness performance of multi-cell conical tubes with new sectional configuration design(i.e.square,hexagonal,octagonal,decagon and circular)has been evaluated under axial and three different oblique loads.The same weight conical tubes were comparatively studied using an experimentally validated finite element model generated in LS-DYNA.Complex proportional assessment(COPRAS)method was then employed to select the most efficient tube using two conflicting criteria,namely peak collapse force(PCF)and energy absorption(EA).From the COPRAS calculations,the multi-cell conical tube with decagonal cross-section(MCDT)showed the best crashworthiness performance.Furthermore,the effects of possible number of inside ribs on the crashworthiness of the decagonal conical tubes were also evaluated,and the results displayed that the tubes performed better as the number of ribs increased.Finally,parameters(the cone angle,θ,and ratio of the internal tube size to the external one,S)of MCDT were optimized by adopting artificial neural networks(ANN)and genetic algorithm(GA)techniques.Based on the multi-objective optimization results,the optimum dimension parameters were found to beθ=7.9o,S=0.46 andθ=8o,S=0.74 from the minimum distance selection(MDS)and COPRAS methods,respectively.

Multiple objective particle swarm optimization technique for economic load dispatch

A multi-objective particle swarm optimization (MOPSO) approach for multi-objective economic load dispatch problem in power system is presented in this paper. The economic load dispatch problem is a non-linear constrained multi-objective optimization problem. The proposed MOPSO approach handles the problem as a multi-objective problem with competing and non-commensurable fuel cost, emission and system loss objectives and has a diversity-preserving mechanism using an external memory (call “repository”) and a geographically-based approach to find widely different Pareto-optimal solutions. In addition, fuzzy set theory is employed to extract the best compromise solution. Several optimization runs of the proposed MOPSO approach were carried out on the standard IEEE 30-bus test system. The results revealed the capabilities of the proposed MOPSO approach to generate well-distributed Pareto-optimal non-dominated solutions of multi-objective economic load dispatch. Com- parison with Multi-objective Evolutionary Algorithm (MOEA) showed the superiority of the proposed MOPSO approach and confirmed its potential for solving multi-objective economic load dispatch.

Optimization design of piles subjected to horizontal loads based on reliability theory

Based on reliability theory,a general method for the optimization design of piles subjected to horizontal loads is presented.This method takes into consideration various uncertainties caused by pile installation,variability of geotechnical materials from one location to another,and so on.It also deals with behavior and side constraints specified by standard specifications for piles.To more accurately solve the optimization design model,the first order reliability method is employed.The results from the numerical example indicate that the target reliability index has significant influence on design parameters.In addition,the optimization weight increases with the target reliability index.Especially when the target reliability index is relatively large,the target reliability index has significant influence on design weight of piles.

Use of Crescent Shaped Braces for Controlled Seismic Design of Ductile Structures

It is known that the seismic response of a structural system is highly influenced, in addition to the earthquake input, by the dynamic characteristics of the system itself. This paper presents an approach for the identification of the characteristics of the structural system resisting to horizontal loads which enables to satisfy given seismic performance objectives. This is achieved by considering a total conceptual separation between the structural systems resisting to vertical and horizontal loads. The proposed approach is first briefly developed in general within a Performance-Based Seismic Design （PBSD） framework and then fully applied to the case study of a five-storey steel building structure. It is composed of three basic steps： （1） identification of the fundamental characteristics which should be possessed by the horizontal resisting system to satisfy a multiplicity of performance objectives, （2） development of a peculiar horizontal resisting system composed of ＂crescent shaped braces＂ which are specifically calibrated to satisfy given performance objectives, （3） verification, by means of appropriate time-history analyses, of the seismic performances achieved. In detail, the horizontal resisting system is calibrated to satisfy a multiplicity of performance objectives through the identification of an ＂objectives curve＂, in the Force-Displacement diagram, of the mechanical characteristics of the structure. The calibration is obtained by methods/tools borrowed either from Direct Displacement-Based Design （DDBD） or Force-Based Design （FBD）, depending on the specific performance objective to be imposed. The applicative example has been carried out with reference to three performance objectives and has led to the identification of a horizontal resisting system composed of special bracing elements capable of realizing a sort of properly-calibrated seismic isolation called crescent-shaped braces. The results obtained through non-linear dynamic analyses have shown that the proposed approach leads to the congruity between the imposed and the achieved seismic performances.

大跨度铁路站房屋盖结构风洞试验与等效静风荷载研究

以哈尔滨西客站站房屋盖结构为研究对象,采用刚性模型同步测压风洞试验对建筑表面的平均及脉动风荷载进行测定,结合本征正交分解技术对风压场进行重构及预测,解决了风压测点与结构有限元模型节点的不匹配问题。分别建立整体结构和屋盖结构有限元模型,利用时程分析方法考察了下部结构对风致响应的影响,研究表明下部结构会导致屋盖结构的刚度弱化,建模中忽略下部结构可能导致对屋盖结构位移和内力响应的低估。引入多目标等效静风荷载分析方法,以结构在风荷载作用下的最大动力响应为控制指标获得针对多个等效目标的静风荷载分布,并对等效结果进行了验证,结果表明该方法可以实现以少量静风荷载分布形式实现所有响应均与动力极值响应等效。