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.     

Thin-walled structures as impact energy absorbers

The key structural components of the majority of transportation vehicles are designed as thin-walled components. During a crash event, a number of structural components must sustain abnormal loadings in order to meet stringent integrity requirements. At the same time other components must dissipate impact energy in a controlled manner that limits the deceleration of a vehicle to a required safety limit. The present paper focuses on the crushing mechanics of thin-walled components. The analysis method is based on the Superfolding Element (SE) concept, which originates from experimentally observed folding patterns of crushed shell elements. The paper presents milestones of the underlying theory of plastic shells and basic design considerations that are coupled with the SE-based predictive techniques in a CAE software. The paper also presents basic examples of the design process of typical energy absorbing components.     

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。     

Metaheuristic optimization within machine learning-based classification system for early warnings related to geotechnical problems

This study proposes a novel classification system integrating swarm and metaheuristic intelligence, i.e., a smart firefly algorithm (SFA), with a least squares support vector machine (LSSVM). Benchmark functions were used to validate the optimization performance of the SFA. The experimental results showed that the SFA obtained 100% success rate in searching the optimum for most benchmark functions. The SFA was then integrated with the LSSVM to create a metaheuristic optimized classification model. A graphical user interface was developed for the proposed classification system to assist engineers and researchers in executing advanced machine learning tasks. The system was applied to several geotechnical engineering problems that involved measuring the groutability of sandy silt soil, monitoring seismic hazards in coal mines, predicting postearthquake soil liquefaction, and determining the propensity of slope collapse. The prediction problems in these studies were complex because they were dependent on various physical factors, and such factors exhibited highly nonlinear relations. The analytical results revealed that the metaheuristic optimization within machine learning-based classification system exhibited a groutability prediction accuracy of 95.42%, seismic prediction accuracy of 93.96%, soil liquefaction prediction accuracy of 95.18%, and soil collapse prediction accuracy of 95.45%. Hence, the proposed system is a promising tool to provide decision-makers with timely warnings of geotechnical hazards.     

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.     

创建国际化勘查型矿业公司———纪念有色金属矿产地质调查中心成立十周年

2001年,原有色地质勘查队伍实行属地化管理,中央编制办公室批准设立有色金属矿产地质调查中心(以下简称有色地调中心或中心).有色地调中心是由原有色地质勘查总局及其未属地化的在京和燕郊直属单位重组而成,下辖5个二级事业单位:北京地质调查所、新疆地质调查所、南方地质调查所、北京勘查技术中心、北京测绘院.     

叠合成矿作用及相关问题

叠合成矿作用是叠加和复合成矿作用的总称.文章对叠合成矿作用、叠加成矿作用、复合成矿作用,以及有关矿床类型的概念进行了诠释;主要总结了5种成矿地质作用及其之间的叠加和复合,及其形成的矿床类型;讨论了叠加成矿作用的类型及相关的7个主要问题;研究了复合成矿作用的3种形式,以及相关的7大类、17种常见矿床类型.强调了叠合成矿作用存在程度和级次上的连续性和过渡性,并进一步指出其在实际矿床研究和找矿勘查工作中的意义,尤其有助于端元矿床类型的找矿.     

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.     

张拉整体高耸结构优化研究

张拉整体高耸结构是一种新型结构体系,是张拉整体在竖直方向上的应用,目前尚未有功能性结构建成。针对一座电视塔的张拉整体高耸结构,采用改进的遗传算法和三级混合算法,依靠有限元分析对结构进行了优化设计。改进的遗传算法能够识别迭代过程中松弛的索,通过自动调整对应编码区的变异率来避免索的松弛,采用非线性求解器对结构的侧向刚度进行优化;三级混合算法包含了模式搜索法、单纯形法和齿行法,采用线性求解器对结构的侧向刚度和自重进行了联合优化,提高侧向刚度的同时减小自重。优化结果表明：这两种优化算法都能够在预应力水平基本不变的情况下大幅提高结构侧向刚度,优化效果良好。     

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.