Thin-walled structures with slotted connections stability problems

In this paper the linear and non-linear stability analyses of elastic structures with unilateral supports or connections are presented. Local and global buckling phenomena are analysed for a wide range of columns’ lengths to encounter coupled instability, which appears when local buckling occurs close to global one. Influence of clearances on buckling and post-critical response is examined. This phenomena is illustrated using simplified models, where the clearances are introduced as translation or rotation gaps. Main attention is focused on modelling the double sigma members, where the cross-sections are composed of two sigma members, connected in discrete points distributed along the webs. The influence of spacing and way of numerical modelling of connectors on buckling behaviour of beams is studied. Numerical examples illustrate the importance of proper modelling of the structures with slotted connections accounting for initial imperfections. The examples are solved using FEM.     

Discrete optimization problems of the steel bar structures

In this paper there are considered the optimal design problems of the elastic and elastic–plastic bar structures. These problems are formulated as nonlinear discrete optimization problems. The cross-sections of the bars are designed from steel rolled profiles. The mathematical models of the problems, including the structural requirements of strength, stiffness and stability, are formulated in terms of the finite element method. The stated nonlinear optimization problems are solved by the iterative method, where each iteration comprises of the selection of the cross-sections of the bars from the assortment and solution of the linear problems of discrete programming. The requirement of discrete cross-sections is ensured by the branch and bound method.     

市政管网优化技术及其相关问题探讨

现阶段,社会经济发展迅速,生产力水平不断提升,且在一定程度上推动着城市基础设施建设的不断发展,而市政管网作为其关键部分,由于不断增大的环境、资源与人口压力,我国政府则逐渐投入到了城市基础建设中,且力度加大,另外,市政管网建设的发展速度也在逐渐加快,已广泛运用了大量新型的市政管网材料与技术,进而保障了我国经济的持续稳定发展。基于此,对市政管网优化技术及其相关问题进行了详细地分析与探究。     

膜结构的多目标形态优化

根据膜结构的力学特点,建立膜结构的多目标形态优化模型,确定"刚度最大"、"受荷后应力分布最均匀"和"支座反力最小"为优化目标,并明确各目标的数学表达形式;重点比较用于描述刚度的三种表达形式(应变能、最大位移和平均位移)在力学概念及优化结果上的区别;通过加权系数法将多目标优化问题转化为单目标问题,并采用遗传算法进行求解;最后,给出相关算例对上述理论和方法进行验证.研究结果表明:膜结构形态优化模型是有效的、实用的;采用不同的刚度描述指标对优化结果影响很大,其中,应变能最能反映膜结构刚度的本质,优化结果也更为合理;结合加权系数法和遗传算法,可以获得各项力学性能均较为理想的优化结果.     

膜结构的概念设计与形态优化

膜结构是一种建筑与结构完美融合的结构形式,"形"和"态"是膜结构设计中的重要概念.为实现形态设计的合理性,国内外学者已开展了大量研究,提出多种形态分析方法.但是形态分析并不等同于形态设计,要实现设计合理性还需要在概念设计和分析结果优化两方面开展工作.本文首先介绍了一些典型膜结构的建筑造型和力学特点,探讨了膜结构概念设计的一些基本原则;然后提出了以"刚度最大"、"受荷后应力分布最均匀"和"支反力最小"为优化目标的基于遗传算法的膜结构多目标形态优化方法;最后应用该方法对几种典型的膜结构进行了形态优化分析,得到了一些可用于指导膜结构概念设计的参数较优取值范围.     

非光滑优化问题的最优性条件和对偶

在函数广义凸意义下 ,获得了非光滑非线性优化问题的最优性必要条件和充分条件 ,建立了问题的对偶模型并得到对偶结果 .     

Shape optimization of thin-walled beam-like structures

This article presents a methodology for optimizing the shape of thin-walled structures having a beam-like dynamic behavior. The equivalent nominal beam characteristics (quadratic moments of inertia, torsional rigidity, etc.) of a refined finite element model are determined from a direct calculation based on explicit equations which are functions of the nodal coordinates defining the cross-sectional geometry. A subset of these coordinates is then taken as the design variables for a nonlinear optimization problem where new target physical properties are sought. A complementary model reduction procedure is introduced to improve the precision of the proposed method for beams with variable cross-section or topological accidents.     

脊谷式膜结构的形态优化分析

建立了以刚度最大、应力分布最均匀和支座反力最小为优化目标,以遗传算法为优化算法的膜结构多目标形态优化方法,对脊谷式膜结构进行了形态优化分析.揭示了在不同荷载形式下脊谷式膜结构的最优形态及其对应的结构参数关系,探讨了荷载大小、结构跨度及膜材预应力等参数对最优形态的影响,并给出了雪荷载与风荷载的组合作用下脊谷式膜结构最优设计参数取值范围,为脊谷式膜结构的设计提供了明确的指导.     

建筑空间结构的设计与优化

从建筑空间结构设计的特点入手,分析了建筑空间结构设计的优化问题,总结了建筑空间结构设计和优化的措施,以期通过对建筑空间结构进行优化,设计出更加美观、经济、安全、合理的建筑物。     

Load combination and related fatigue reliability problems

After a general formulation for the load combination problem is sketched, attention is focused on the practical rules to be used in structural design. Three main aspects are found to require further developments:

1. 1. the flexibility of the combination rule to incorporate special situations;

2. 2. the load factor calibration;

3. 3. the understanding of the features the load combination idealization requires when the reliability against a fatigue limit state is studied.

A discussion of these three items forms the core of the paper. Some numerical simulations are also carried out in order to exemplify the fatigue reliability problem.     

Loadbearing problems in high-rise panel structures

When panel construction is used for buildings exceeding five or six storeys new factors are introduced over and above those which occur in conventional forms of high rise construction, say the authors, who are research scientists working in Hungary. Panel construction at these heights is subject to a greater degree of spatial force because of the greater rigidity of the panels, and the design of floor plans and the loadbearing characteristics of the structure must be carefully coordinated.     

Loadbearing problems in high-rise panel structures

When panel construction is used for buildings exceeding five or six storeys new factors are introduced over and above those which occur in conventional forms of high rise construction, say the authors, who are research scientists working in Hungary. Panel construction at these heights is subject to a greater degree of spatial force because of the greater rigidity of the panels, and the design of floor plans and the loadbearing characteristics of the structure must be carefully coordinated.     

Thin-walled thermoplastic pipes

Stressed skin and rib-reinforced shell structures optimize plastics pipe performance. Computation of engineered pipes is easy as they can be substituted for by orthotropic pipes having the same rigidity characteristics. The flexible pipe theory lends itself very well to the concept of thin walled plastics pipes predicting a 100-year design life. Practical experiences are studied as well as other dimensioning aspects, e.g. buckling, impact resistance and minimum wall thickness. Combinations of various construction principles and materials have different performance characteristics making market segmentation optimal.     

Design optimization and experimental study on beam string structures

Taking the beam string structure (BSS) in Shanghai Yuanshen Arena as a sample, the rise-span ratio, beam cross-section, area of string, prestressing force of BSS was optimized by using the ANSYS programme. It was proposed that the absolute value of the maximum deflection of the beam under dead load should be minimized in the optimization of the prestressing force. Based on three scale model tests and elastoplastic large deformation analysis, the paper investigated the behavior of BSS in the full-range including the stretching phase, serviceability phase and ultimate load carrying phase. The results showed that the midspan camber should be chosen as the control target of stretching. The failure mode of BSS was the yielding or rupture of the string, while the beam was still in the semi-plastic stage. This paper also presented the construction monitoring results of the real BSS, which satisfied design requirements well.     

GPS网优化设计中个别问题的研究

利用GPS卫星进行定位技术是建立各种用途控制网非常重要的方法,本文针对GPS网优化设计中个别问题提出了几点建议,可为从事高精度GPS测量工作在实际应用时参考使用,达到提高GPS控制网的可靠性、精度以及提高工作效率和经济效益的目的。     

Dual coordination of decomposed dynamic optimization problems

The dynamic optimization of large interconnected sets of differential equations in state space form is considered within the context of some civil engineering applications. The theorems of duality for static problems are extended to the dynamic case to provide the basis for an iterative two-level computational algorithm based on price directive dual coordination. Computational results from a number of spatially and time decomposed applications are presented, including production and inventory planning, minumum energy operation of water supply networks, urban traffic transportation systems, and environmental pollution control. These computational schemes may be of more general interest to other areas of civil engineering optimization to which they have not yet been applied.     

启发式粒子群优化算法及其在空间结构优化中的应用

介绍了应用于结构离散变量的标准粒子群优化算法(PSO)及被动群集的粒子群优化算法(PSOPC),指出了两者在处理约束条件方面的不足之处.在基于“和谐搜索“算法(Harmony Search)产生新解的思想基础上,提出了应用于结构离散变量的启发式粒子群优化算法(HPSO).应用所提出的HPSO算法对多个平面及空间桁架结构进行了截面优化设计,数值计算结果表明本文提出的启发式粒子群优化算法(HPSO)可以搜索到最优解,并且具有较高的收敛速度,尤其在迭代计算的初期,计算效率非常明显.HPSO算法明显提高了PSO算法的效率.     

Buckling and imperfection sensitivity in the optimization of shell structures

The subject of the present study is the optimization of structures with geometrically nonlinear behaviour allowing the inclusion of instability phenomena and imperfection sensitivity in the structural design. The proposed optimization procedure is based on the methods of path following, direct computation of bifurcation and limit points and an accurate and efficient sensitivity analysis. The finite element method is used for the structural analysis. These techniques are used together with mathematical programming schemes and methods of computer-aided geometric, design.