基于水平集方法的连续体结构拓扑优化

提出了一种用水平集函数作为设计变量求解连续体结构拓扑优化的方法。优化方法以结构的整体柔度最小为目标函数,以实体材料所占的体积为约束条件,综合采用有限元方法和优化准则法对问题进行求解。该方法与密度惩罚法相比,克服了锯齿形边界,得到了光滑的结构边界;与传统水平集方法相比,不用求解复杂的Hamilton-Jacobi方程,提高了计算效率。在对Heaviside函数正则化处理中,考虑了形状导数和拓扑导数信息,加快了收敛速度。用该方法对梁的拓扑优化设计进行了试算,得到了满意的优化结果。     

弦支双曲扁网壳结构的鲁棒构型分析及试验研究

针对不良拓扑布置导致的结构鲁棒性不佳问题，以系统传递函数的H₂范数为基础，建立结构鲁棒性定量评价指标和鲁棒构型求解方法。以单元相对密度为设计变量，采用变密度模型描述材料的刚度，将结构的鲁棒设计转化为连续体拓扑优化，并对大爆炸算法进行二级搜索的改进，进而求解连续体拓扑优化模型。以四点支承的弦支双曲扁网壳结构为例，分析不同荷载作用下的鲁棒构型，探索不同参数的大爆炸算法优化效果，通过静力试验和冲击试验，对优化后模型和未优化模型进行对比分析。结果表明，二级搜索的大爆炸算法可以有效地应用于弦支结构的鲁棒设计中，改进的大爆炸算法加快了收敛速度，依据鲁棒构型进行杆件布置，可显著提高结构的力学性能和抗干扰能力。     

基于工程限值约束的结构拓扑优化设计分析

基于固体各向同性材料惩罚密度插值模型,建立近似支撑框架模型,以最大刚度为优化目标,以优化体积比及工程限值为约束条件,对支撑框架结构进行了优化。工程限值约束包括最大、最小尺寸约束,对称性约束以及顶点位移约束等。研究结果表明：当支撑框架中斜撑的斜交角度为39°~59°时,框架具有较好的抗侧刚度;当优化体积比为0.3时,优化后结构顶点位移较原设计域增加19%。引入工程限值约束条件能使拓扑优化后的结果有效应用于实际工程,优化后结构具有框架形态,无不易建造的细微结构,减少了低效材料分布,从而降低造价。     

Configuration optimization of clamping members of frame-supported membrane structures

A method is presented for configuration optimization of frames that have specified properties on nodal displacements, stresses, and reaction forces against static loads. The conventional ground structure approach is first used for topology optimization. A feasible solution with a small number of members satisfying all the design requirements except the stress constraints is obtained by assigning artificially small upper-bound displacement, or by penalizing the stiffness of a thin member. This way, the well-known difficulty in topology optimization under stress constraints is successfully avoided. The nodal locations and cross-sectional areas of the feasible solution are next optimized to obtain an approximate optimal configuration under stress constraints. The proposed method is applied to the design of self-fastening clamping members for membrane structures modeled using frame elements. An optimization result is also presented for a clamping member that adjusts deformation of membrane by applying a clamping force with a vertically attached bolt.     

Optimal design of Schwedler and ribbed domes via hybrid Big Bang-Big Crunch algorithm

An optimum topology design algorithm based on the hybrid Big Bang-Big Crunch optimization (HBB-BC) method is developed for the Schwedler and ribbed domes. A simple procedure is defined to determine the Schwedler and ribbed dome configuration. This procedure includes calculating the joint coordinates and element constructions. The nonlinear response of the dome is considered during the optimization process. The effect of diagonal members on the results is investigated and the optimum results of Schwedler domes obtained by the HBB-BC method demonstrate the efficiency of these domes to cover large areas without intermediate supports.     

Optimal design of steel frames under seismic loading using two meta-heuristic algorithms

In this paper, optimal design of steel frames is performed under seismic loading. The variables of the problem are taken as the cross-sectional areas of the members. These variables are considered as discrete, and are selected from a list of existing cross sections. Here, the charged system search and improved harmony search algorithms are utilized for optimization. For optimal design of steel frames in the first phase a time history analysis with the relative lateral displacement constraints is performed, and in the second phase a simultaneous dynamic–static analysis with the relative displacement and stress constraints is utilized using two meta-heuristic algorithms. Moment frames and their shear frame counterparts are considered, and their performances are compared for optimal design. In the case of moment frames, apart from the columns, the cross sections of the beams are also considered as design variables. The results indicate a good performance of the optimized moment frame and show that considering the effect of both drift and stress constraints, instead of only drift constraints, one obtains a better design. These results also show the suitability of the charged system search algorithm for optimal design of frames under seismic loading, as an extremely nonlinear problem.     

空间结构节点的拓扑优化与增材制造

在简要介绍连续体结构拓扑优化的数学描述和数值算法的基础上,建立一空间结构节点模型,利用优化软件OptiStruct对节点进行单工况和多工况下的拓扑优化设计。详细讨论了棋盘格控制、SIMP法密度插值惩罚系数等参数设置以及对称约束、成员尺寸约束等工艺制造约束对优化结果的影响。经多次尝试比较得到受力合理、外观简洁且具有设计美感的优化节点模型,并利用熔融沉积制造技术完成采用聚乳酸材料的节点打印。文中进一步讨论了实际工程中利用增材制造（3D打印）技术对优化模型进行制造成型的可行性。目前易于实现的途径是将增材制造和传统制造工艺结合起来,如利用3D打印制作复杂铸钢节点的模具、3D打印蜡模进行失蜡铸造等。     

输煤栈桥钢材选型的优化分析

针对输煤栈桥及支架用钢量偏大的问题,提出用等截面圆钢替代工字钢用于合理选取优化变量,及分段设置优化参数的方法,减少了栈桥及灯笼架结构优化所需要的优化变量。利用ANSYS软件中的优化技术,对某煤场输煤栈桥及支架方案的用钢情况进行了优化,分析了优化结果的静、动力特性,并与原方案进行了比较。优化后方案在最大变形、最大应力及动态特性等方面同原方案无明显差别或优于原方案,但各构件的承载能力得到更好的发挥,用钢总量较原方案明显减少。     

有支撑钢框架离散型拓扑优化设计

为了研究离散型拓扑优化理论在实际工程中的应用,在遗传算法和渐进结构优化算法的基础上对有支撑钢框架的离散型拓扑优化设计进行了分析.通过引入拓扑变量并修改无效杆件的弹性模量,提出了一个能适用于桁架结构、刚架结构和桁架刚架混合结构的离散型拓扑优化问题统一数学列式.该统一数学列式能解决桁架拓扑优化问题中以截面面积作为设计变量而...     

Topology optimization and seismic collapse assessment of shape memory alloy (SMA)-braced frames: Effectiveness of Fe-based SMAs

This paper presents a seismic topology optimization study of steel braced frames with shape memory alloy (SMA) braces. Optimal SMA-braced frames (SMA-BFs) with either Fe-based SMA or NiTi braces are determined in a performance-based seismic design context. The topology optimization is performed on 5- and 10-story SMA-BFs considering the placement, length, and cross-sectional area of SMA bracing members. Geometric, strength, and performance-based design constraints are considered in the optimization. The seismic response and collapse safety of topologically optimal SMA-BFs are assessed according to the FEMA P695 methodology. A comparative study on the optimal SMA-BFs is also presented in terms of total relative cost, collapse capacity, and peak and residual story drift. The results demonstrate that Fe-based SMA-BFs exhibit higher collapse capacity and more uniform distribution of lateral displacement over the frame height while being more cost-effective than NiTi braced frames. In addition to a lower unit price compared to NiTi, Fe-based SMAs reduce SMA material usage. In frames with Fe-based SMA braces, the SMA usage is reduced by up to 80%. The results highlight the need for using SMAs with larger recoverable strains.     

四分叉铸钢节点拓扑优化及3D打印制造

针对铸钢节点质量过大和应力分布不均衡等问题,采用拓扑优化的方法对竖向荷载作用下四分叉铸钢节点的最优形态进行了研究。利用SolidWorks三维建模软件建立原始节点模型并应用HyperWorks有限元软件中的OptiStruct求解器对其进行了拓扑优化,分析惩罚因子、棋盘格控制等优化参数的影响,经多次对比调试得到四分叉铸钢节点的最优拓扑模型。以两种实际工程节点为算例,分析拓扑优化方法用于节点优化设计的实际效果。将拓扑优化节点有限元模型转化为STL文件,并将其导入切片软件中进行代码编译,应用FDM技术、SLM技术及快速铸造工艺等3D打印方式制造拓扑优化节点的缩尺模型。研究结果表明：拓扑优化可以在保持节点良好力学性能的同时降低铸钢节点的自重,利用拓扑优化的方法寻找铸钢节点的最佳形态是有效可行的;3D打印技术应用于节点制造,不仅可以显著改善制造精度,还可以解决拓扑优化形成的复杂形体采用传统工艺难以制造的关键问题。     

北京天文馆新馆有限元分析

北京天文馆新馆采用以钢骨混凝土框架 -支撑结构为主的新型抗震结构体系。该工程结构体系复杂 ,应用ANSYS有限元分析程序对天文馆新馆进行了静、动力反应分析计算 ,为结构构件设计提供依据。着重讨论了地震作用下支撑构件的耗能作用 ,得出一些指导工程实践有益的结论。     

超高层建筑顶升模架系统的优化设计及智能建造

为研究超高层建筑顶升模架系统优化设计与现场智能化施工的数字化融合,提高材料使用效率和结构合理性,以西安某超高层建筑中所使用的顶模钢框架结构为对象,采用SIMP插值模型法,约束次桁架悬挑端竖向位移,以减少顶模钢框架结构钢材用量为目标进行优化,依据优化结果对顶模钢框架结构进行设计。应用智能建造与建筑工业化协同发展的研究成果,以拓扑优化设计、系统化安装、智能化施工为实施框架,通过拓扑优化设计结合智能化控制操作等工具,实现基于智能建造的优化型顶模钢框架结构; 系统梳理智能建造各阶段应用,利用施工管理平台,实现基于信息化模型的工程管控。结果表明:优化后顶模钢框架结构在满足约束条件情况下,在提升结构承载能力、刚度的同时,使钢框架自身重量减轻20%,降低了顶模钢框架结构用钢量,提升了钢材的使用效率,加强了拓扑优化设计与现场智能化施工的数字化融合,推动了智能化施工装备的施工应用。     

拉索对索-桁穹顶结构的敏感性影响分析

索-桁穹顶结构中拉索的施工是该种结构的难点和关键点.在实际施工中,拉索的初始预应力值往往难以与设计值完全一致,因此,研究拉索对索-桁穹顶结构的敏感性,指出具体拉索是否具有敏感性,对设计与施工均有指导意义.本文采用正交设计分析法,对索-桁穹顶结构中的拉索按L8建立正交表,分别研究了拉索对该种结构的静力、动力及稳定性的敏感程度.结果表明,外环索对结构的性能甚为敏感,内环索对结构的动应力较为敏感,而斜索对结构的稳定性十分敏感.     

Progressive collapse analysis of steel frames: Simplified procedure and explicit expression for dynamic increase factor

Progressive collapse refers to a phenomenon in which local damage in a primary structural element leads to total or partial structural system failure. When investigating the progressive collapse of structures, nonlinear dynamic procedures lead to more accurate results than static procedures. However, nonlinear dynamic procedures are very complicated and the evaluation or validation of the results can become very time consuming. Therefore, it is better to use simpler methods. For static analyses, the gravity force applied to the removed column bay should be multiplied by a constant factor of two. However, using a constant dynamic increase factor (DIF) is only appropriate for elastic systems. According to the optimal design of structures, the assumption of elastic behavior after column removal is conservative. Thus, it is necessary to establish an expression for DIF that considers inelastic responses. In this paper, a simplified analysis procedure for the progressive collapse analysis of steel structures is presented using the load displacement and capacity curve of a fixed end steel beam. The results of the proposed method are in good agreement with nonlinear dynamic analysis results. Also, the capacity curve, obtained by dividing the accumulated area under the nonlinear static load displacement curve by the corresponding displacement of the column removed point, is used to predict the progressive collapse resistance of the column removed structure. Finally, an explicit expression for the DIF is established for elastic-perfectly plastic and elastic plastic with catenary action behavior.     

Nonlinear dynamically automated excursions for rubber-steel bearing isolation in multi-storey construction

Conventional building design includes the concept of providing more stiff structural solution to withstand the lateral seismic loading. Introduction of flexible elements at the base of a structure and at the same time ensuring enough damping is the evocative alternate option to mitigate seismic hazard. The device that is capable to meet such criteria is known as isolator. This paper covers design of base isolators for multi-storey buildings in medium risk seismicity region and the structural response evaluation. Automated nonlinear models for dynamic response investigation have been configured. Finite element method (FEM) has been incorporated to envisage the structural response behaviors. Lead rubber bearing (LRB) and high damping rubber bearing (HDRB) have been chosen for inserting isolator link element in structural base. The nonlinearities of rubber-steel bearing have been duly considered. Linear static, linear dynamic and nonlinear dynamic analyses due to site-specific earthquake accelerogram are performed for both fixed based (FB) and base isolated (BI) buildings. Both time domain and frequency domain approaches have been carried out for dynamic solution. It was found that for multi-storey buildings, base isolation diminishes muscular amount of structural responses compared to the conventional fixed base (non-isolated) structures. Allowable higher horizontal displacement induces structural flexibility. The suggested isolation technique is competent to mitigate the structural hazard even under strong seismic vulnerability in optimum manner.     

On the characteristics of new ductile knee bracing systems

In this paper, a new structural lateral bracing system called ‘Chevron Knee Bracing’ (CKB) is investigated. This new form of framing system is constructed through the knee and the diagonal brace elements. The knee part is a fuse-like component that dissipates energy by the formation of plastic flexural and/or shear hinges at its ends and mid-span, when the building is subjected to severe lateral loads. However, the diagonal brace component, on the other hand, provides the required level of lateral stiffness and remains in the elastic range without buckling at any time. In this investigation, first, by studying of the system in the elastic region, three new and practical parameters are established. Then, the best fitting optimal shape and angle of the knee and brace elements are projected, analytically. In the next step, by developing a nonlinear analytical knee element model, the actual behavior of this new CKB system is experienced in the nonlinear static and dynamic analysis, on two example structural systems, where the knee element happens to be in the moment and/or shear yielding mode. Using the results on nonlinear analysis of these test problems, the main properties of the CKB, such as the energy dissipation characteristics of the proposed systems, are properly inspected by establishment of an energy calculation algorithm. Finally, based on the presented optimal shape of the CKB in this paper, two step-by-step algorithms accompanied by appropriate main graphs and charts are suitably demonstrated and nonlinear behavior of the new model for flexural and shear yielding modes is well determined, which is followed in the next paper.     

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.     

深基坑新型钢斜撑接头承载力试验研究

 提出一种深基坑新型钢斜撑接头形式,它可以即插即用,允许有一定的转动角度,可施加预应力,克服原有斜撑接头焊接施工增加基坑暴露时间、倾斜角度固定给斜撑安装带来不便、焊接后无法施加预应力等缺点,可使软土地区深基坑施工受时空效应影响明显减小。配合接头试验制作自平衡式试验架。按照实际尺寸,对该新型支撑接头进行承载力试验,加载到设计轴力2 500 kN时,接头承载力满足设计要求,加载到3 000 kN时接头局部达到屈服状态,预埋钢匣子前方混凝土局部出现压碎现象,但结构整体稳定。用有限元法进行加载过程数值模拟计算,计算曲线与实测吻合较好,这种新型斜撑接头可以进一步推广应用。     

约束条件对天津极地海洋馆网壳结构性能的影响

天津极地海洋馆钢结构屋盖根据仿生学原理模拟鲸鱼的外形。"鲸鱼"身长275m,宽117m,高45.6m,采用双层网壳结构模拟;尾部背鳍高69.4m,采用空间管桁架结构模拟。通过对其屋盖钢结构主体的有限元分析,主要研究了双层网壳结构在弹性支座和固定铰支座两种不同约束条件下的静力性能、动力特性和抗震性能,分析支座刚度对网壳结构性能的影响。相比固定铰支座,弹性支座可以明显地改善屋盖双层网壳结构的力学性能,对相关课题研究及工程设计具有一定的理论价值与实用意义。