Optimal design of water distribution systems

In this paper, the similarities between a water distribution system (WDS) and a structural truss are discussed. Based on this discussion, the problem of determining the optimal design of a WDS is studied by extending some of the methods used to good effect in structural optimization. Two sensitivity analysis methods for node heads, i.e. virtual-discharge method and pseudo-discharge method, are proposed, and the sensitivity formula for pipe flowrates is derived. An algorithm based on the Sequential Linear Programming (SLP) technique is suggested. Finally, two numerical examples are presented.     

Reliability-based optimization in structural engineering

In this paper reliability-based optimization problems in structural engineering are formulated on the basis of the classical decision theory. Several formulations are presented: Reliability-based optimal design of structural systems with component or systems reliability constraints, reliability-based optimal inspection planning and reliability-based experiment planning. It is explained how these optimization problems can be solved by application of similar techniques. The reliability estimation is limited to first order reliability methods (FORM) for both component and systems reliability evaluation. The solution strategies applying first order non-linear optimization algorithms are described in detail with special attention to sensitivity analysis and stability of the optimization process. Furthermore, several practical aspects are treated as: Development of the reliability-based optimization model, inclusion of the finite element method as the response evaluation tool and how the size of the problem can be made practicable. Finally, the important task of model evaluation and sensitivity analysis of the optimal solution is treated including a strategy for model-making with both pre and post-analysis.     

周期与层间位移角双约束条件下超高层结构优化设计方法

基于地震作用下层间位移角和一阶周期对构件材料成本的敏感性系数计算公式的推导，提出了双约束条件下结构优化组合排序法。结合一两层平面框架算例，分别采用建议公式和等增量敏感性分析方法计算了设计约束对构件材料成本的敏感性系数，并进行了对比；以某超高层结构为研究对象，采用提出的计算公式和组合排序法对结构进行了敏感性分析和结构优化。结果表明：采用建议的计算公式和等增量敏感性分析方法得到的敏感性系数较吻合，说明建议公式具有较高的准确性；采用组合排序法进行双约束条件下的结构优化时，当控制每组构件材料成本变化量不超过10%时，设计约束对构件材料成本的敏感性系数可认为是不变量；在初始优化阶段，设计约束改变较慢，当不敏感构件组的构件优化完成后，主要改变较敏感构件组的构件，使设计约束加速收敛至限值；优化过程中出现了最大层间位移角所在楼层交替变化的情况，可采用比规范更加严格的限值来进行结构优化，从而保证实际的设计约束条件满足规范限值要求。     

Optimized topology extraction of steel-framed DiaGrid structure for tall buildings

This study presents an optimal angle and a topology extraction of diagonal members in a DiaGrid structural system for tall buildings. The angle and topology of diagonal members are achieved by using a computer-oriented SIMP topology optimization. The objective function for the design optimization is to both maximize Eigenfrequency for resisting dynamic responses and minimize mean compliance for static responses. Relative densities subjected to SIMP penalty law are used for both optimization design variables and material properties, and then finite element analysis is carried out by using the relative element density. Frequency and mean compliance sensitivities with respect to relative density are straightforwardly derived by discrete sensitivity formulations. Based on the design sensitivity analysis, an initial topology with a given fixed support is shifted toward a final topology charged by almost voids (0) and solids (1) during every optimization procedure. An optimal DiaGrid topology with the highest stiffness is finally determined to resist both static and dynamic behaviors. Numerical examples with varied fixed support models are studied to find out optimal angles and topologies of diagonal members for a DiaGrid system design.     

基于灵敏度分析和优化方法的异形钢结构烟囱模型修正

为了给异形钢结构烟囱的抗风、抗震计算及健康监测提供可靠的有限元计算模型,采用钢结构烟囱风洞试验模型的模态参数作为基准,将灵敏度分析和优化方法与大型有限元分析软件相结合修正烟囱结构模型的有限元模型。首先对烟囱结构参数化建模,然后通过灵敏度分析选择合适的优化变量,最后应用一阶优化方法修正烟囱结构的有限元模型。结构构件间连接的过分简化常会带来较大误差,因此烟囱结构的部分连接节点采用半刚性计算模型。结果表明,经过修正后的有限元模型动力计算结果与试验结果非常接近。     

Novel decoupled framework for reliability-based design optimization of structures using a robust shifting technique

In a reliability-based design optimization (RBDO), computation of the failure probability (P_f) at all design points through the process may suitably be avoided at the early stages. Thus, to reduce extensive computations of RBDO, one could decouple the optimization and reliability analysis. The present work proposes a new methodology for such a decoupled approach that separates optimization and reliability analysis into two procedures which significantly improve the computational efficiency of the RBDO. This technique is based on the probabilistic sensitivity approach (PSA) on the shifted probability density function. Stochastic variables are separated into two groups of desired and non-desired variables. The three-phase procedure may be summarized as: Phase 1, apply deterministic design optimization based on mean values of random variables; Phase 2, move designs toward a reliable space using PSA and finding a primary reliable optimum point; Phase 3, applying an intelligent self-adaptive procedure based on cubic B-spline interpolation functions until the targeted failure probability is reached. An improved response surface method is used for computation of failure probability. The proposed RBDO approach could significantly reduce the number of analyses required to less than 10% of conventional methods. The computational efficacy of this approach is demonstrated by solving four benchmark truss design problems published in the structural optimization literature.     

Machine Learning User Preferences for Structural Design

Abstract: The design process often proceeds through iterative stages of design configuration, analysis, evaluation, and redesign with the ultimate goal of optimization. Numerical methods for structural design optimization of only one attribute such as weight, strength, or cost are well known. However, these methods do not reflect the fact that designs are evaluated by the user in terms of their performance in several attributes. It has been extremely difficult to incorporate multiple attributes into design optimization algorithms because the acceptable tradeoffs between these attributes vary significantly between users.
This paper presents a new method for learning user-specific preferences and integrating them into the design evaluation, analysis, and optimization process in a meaningful way. The approach is a synthesis of formal decision theoretic methods with conventional design analysis techniques. The overall design objective is optimization of multiattribute utility from the viewpoint of the user.
A user-interactive computer-aided Multiattribute Structural Design Evaluation and Optimization System (MSDEOS) is presented. It enables machine learning of the user's willingness to make tradeoffs between performance attributes. With this system, it is feasible to integrate site-specific consideration of multiple attributes directly into computer aids for structural design optimization. Two examples are presented: seismic design, where tradeoffs are made between cost and damage index, and design of a three-story steel frame structure, where attributes are cost and drift index. The system learns the preferences of different users and reflects those preferences through the identification of a different optimal solution for each user.     

MIDAS在大学生结构设计竞赛中的应用

大学生结构设计竞赛是培养土木工程专业学生创造精神、动手能力和团队协作意识的重要平台。文章提出概念设计、优化分析、模型制作是结构设计竞赛的三个重要方面,对比分析了目前国内常用结构分析软件的特点,提出MIDAS是指导大学生进行结构模型优化分析的一个很好工具。以湖南省大学生第四届结构竞赛为背景,总结了MIDAS建模分析基本流程及其关键要点,供模型比选、结构优化设计参考。     

Drift design of steel‐frame shear‐wall systems for tall buildings

Drift design methods based on resizing algorithms are presented to control lateral displacements of steel‐frame shear‐wall systems for tall buildings. Three algorithms for resizing of structural members of the steel‐frame shear‐wall systems are derived by formulating the drift design process into an optimization problem that minimizes lateral displacement of the system without changing the weight of a structure. During the drift design process, cost‐effective displacement participation factors obtained by the energy method are used to determine the amount of material to be modified instead of calculating sensitivity coefficients. The overall structural design model with the drift design method for the steel‐frame shear‐wall systems is proposed and applied to the structural design of three examples. As demonstrated in the examples, the lateral displacement and interstorey drift of a frame shear‐wall system can be effectively designed by the drift design method without the time‐consuming trial‐and‐error process. Copyright © 2002 John Wiley & Sons, Ltd.     

基于建筑空间布置规则性的结构优化分析

结构体系中的大空间或者核心筒的布置不规则,会给建筑抗震设计带来诸多困扰。提出优化设计的方法用于对结构刚度进行调整,以降低建筑空间布置不规则的影响。优化方法是基于进化结构优化法,建立新的灵敏度定义,以修正建筑空间布置规则性为设计目标,优化结构体系中抗侧体系的刚度分布。从建立结构模型开始,直接从建筑设计模型中,提取必要的设计参数,导入优化设计程序中进行建模,提高了建模的效率和准确度。在有限元分析过程中全部采用壳单元,并且在考虑解析准确度的基础上对壳单元进行分割,应用泰森多边形理论对荷载进行计算。在优化计算中,主要从结构整体等效应力分布的均匀性,重心与刚心的相对位置关系以及结构的两向抗侧刚度比三个方面对结构体系的应力、水平以及竖向构件刚度分布进行优化设计,调整建筑空间布局以满足布置的规则性,对进一步深化设计提供可参考的分析结果。     

Cyber‐physical approach to the optimization of semiactive structural control under multiple earthquake ground motions

This paper presents a cyber‐physical approach to optimize the semiactive control of a base‐isolated structure under a suite of earthquakes. The approach uses numerical search algorithms to guide the exploration of the design space and real‐time hybrid simulation (RTHS) to evaluate candidate designs, creating a framework for real‐time hybrid optimization (RHTO). By supplanting traditional numerical analysis (i.e., finite element methods) with RTHS, structural components that are difficult to model can be represented accurately while still capturing global structural performance. The efficiency of RTHO is improved for multiple design excitations with the creation of a multiinterval particle swarm optimization (MI‐PSO) algorithm. As a proof‐of‐concept, RTHO is applied to improve the seismic performance of a base‐isolated structure with supplemental control. The proposed RTHO framework with MI‐PSO is a versatile technique for multivariate optimization under multiple excitations. It is well suited for the accurate and rapid evaluation of structures with nonlinear experimental substructures, in particular, those that do not undergo permanent damage such as structural control devices. The RTHO framework integrates popular optimization algorithms with advanced experimental methods, creating an exciting new cyber‐physical approach to design.     

工业建筑结构的设计优化

随着国民经济的发展,工业建筑得到了大力发展,对工业建筑结构设计的合理性也提出了更高的要求。本文主要从工业建筑结构设计的基本原则和优化方法做了分析,并通过举例对工业建筑结构的设计优化进行了阐述。     

基于改进双向渐进结构优化法的桁架结构拓扑优化

为了将双向渐进结构优化法应用于桁架结构优化设计中,结合能量原理和满应力设计准则,推导了以结构最小应变能为目标函数的优化计算公式,提出了可以应用于桁架结构优化的桁架-双向渐进结构优化(T-BESO)法.T-BESO法以杆件截面面积为设计变量,以结构应变能为目标函数,以应力约束和满应力设计准则为约束条件.在T-BESO法中...     

大学生结构设计竞赛中的结构创新设计与优化

全国大学生结构设计竞赛是土木工程学科培养大学生创新精神、团队意识和实践能力的最高水平学科竞赛。第十届全国大学生结构设计竞赛与往届相比,命题中引入了刚柔并济的思想,除了要求结构具有足够的承载力,还对结构正常使用极限状态下结构的跨中挠度做了限制。从第十届全国大学生结构设计竞赛特等奖作品入手,分析特等奖作品的结构选型和结构优化方法,以期为学生准备结构设计竞赛提供参考。     

Efficient algorithms for the reliability optimization of tall buildings

Modern tall buildings are often characterized by their slenderness and sensitivity to extreme wind events. For these buildings traditional least weight optimization procedures based on a few idealized equivalent static wind loads derived from directionless wind models may be inadequate. This is especially true considering traditional models used for combining aerodynamics and site specific climatological information. Indeed these methods were developed for buildings with statistically and mechanically uncoupled systems exhibiting strong preferential behavior for certain wind directions. Using these models during a traditional deterministic optimization may lead to unsafe designs. In this paper a recently developed component-wise reliability model is used to rigorously combine the directional building aerodynamics and climatological information. An efficient reliability-based design optimization scheme is then proposed based on decoupling the traditionally nested optimization loop from the reliability analysis. The decoupling is achieved by assuming the level cut sets containing the mean wind speeds generating a response with specified exceedance probability independent of changes in the design variable vector. The decoupled optimization problem is solved by defining a series of approximate explicit sub-problems in terms of the second order response statistics of the constrained functions.     

Border-search and jump reduction method for size optimization of spatial truss structures

This paper proposes a sensitivity-based border-search and jump reduction method for optimum design of spatial trusses. It is considered as a two-phase optimization approach, where at the first phase, the first local optimum is found by few analyses, after the whole searching space is limited employing an efficient random strategy, and the second phase involves finding a sequence of local optimum points using the variables sensitivity with respect to corresponding values of constraints violation. To reach the global solution at phase two, a sequence of two sensitivity-based operators of border-search operator and jump operator are introduced until convergence is occurred. Sensitivity analysis is performed using numerical finite difference method. To do structural analysis, a link between open source software of OpenSees and MATLAB was developed. Spatial truss problems were attempted for optimization in order to show the fastness and efficiency of proposed technique. Results were compared with those reported in the literature. It shows that the proposed method is competitive with the other optimization methods with a significant reduction in number of analyses carried.     

预应力局部单双层扁网壳的参数分析与近似优化

预应力局部单、双层扁网壳具有较好的室内视觉效果和良好的经济性。其结构参数的确定属多级别优化问题,实施困难。为满足初步设计的需要,提出采用均匀设计法进行结构的参数分析与近似优化。它可利用现有软件来实现。作为算例,对一个柱支承预应力扁网壳进行了参数分析,得到了网壳用钢量、变形和极限荷载系数与三个主要设计参数(单层部分材料设计应力折减系数、单层部分范围和预应力值)之间的近似函数关系,并找出了满足规范要求的各参数之间的较理想的最优水平组合。设计检验说明了分析结果的可靠性。该方法可为解决类似优化问题提供参考。     

基于Ansys二次开发的网架结构优化设计

通用有限元软件Ansys具有强大的结构分析能力,但由于没有内嵌中国的设计规范,因此其分析结果一般不能直接作为设计结果来使用.本文将设计规范和常用的杆件类型通过APDL二次开发技术内嵌入Ansys中,并在其中进行优化分析计算,实现了在Ansys中一次性完成网架结构的分析与优化设计工作.     

Thin-walled structures and related optimization problems

The present paper deals with specific methods for optimal design of thin-walled structures and with the problem of optimal design for serviceability and ultimate limit state. A brief classification of structural optimization is given first, followed by a general formulation of the optimal design problem for thin-walled structures and by a discussion of the design models involved. Specific solution techniques which have been found to be suited for structural optimization and selected applications are presented.     

基于等增量敏感性的高层建筑结构反向约束优化设计方法研究

以高层建筑结构为背景,提出了一种降级反向约束优化设计方法。降级反向约束优化设计方法根据工程设计习惯,按照整体、组件、构件、截面、构造的顺序逐级收紧设计约束条件,在每一轮设计中采用等增量敏感性分析方法,以最小的结构材料增量弥补本级冗余不足的设计准则,在满足规范安全性的同时,减少结构材料浪费。应用反向约束优化设计方法,对一个10层钢框架结构和一幢实际超高层钢结构进行了基于等增量敏感性的优化设计,并与正向约束优化设计方法的结果进行对比。研究结果表明,结构能够满足规范各项设计准则的要求,在充分满足安全性要求的同时,有效减少了结构材料用量,两个案例材料用料分别减少了14.2%和7.8%,且在优化过程中没有出现约束条件偏离限值的情况,提高了优化效率。