Symmetry breaking: The effect of randomizing mass and stiffness on building response to winds and earthquakes

Symmetry-breaking can have profound consequences for the response of periodic structures. Examples of such structures include tall buildings and their response to winds and earthquakes; repeated trusses in bridge structures and, similarly, repeated trusses for space vehicles; there are many others. These results are discussed for various dampings, various building heights and various excitations with a view to finding building response. Variation of up to ± 20% in the parameters shows displacements (RMS or maximum) of up to two to three times those for the deterministic structure (no variation in parameters). Buildings of 3 to 50 floors are considered. The greatest effects are seen near lower frequency resonances for all structures. The biggest effects are seen for the tallest structures: in such cases amplification of up to a factor of four occur.     

北京庄胜广场中央楼空腹桁架结构施工支撑

北京庄胜广场中央楼２４ｍ跨多层空腹桁架是该工程结构施工的重点控制部位，其关键是保证空腹桁架梁的挠度值的设计允许范围内，为此采取措施利用脚手钢管支设荷载近６万ｋＮ的空腹桁架施工支撑，保证了支撑抗侧移的性能。     

Geometric nonlinear analysis of tall building structures with outriggers

In this paper, the geometric nonlinear behavior of wall‐frame tall building structures is analyzed. The governing equations of the wall‐frame systems with outrigger trusses are formulated through the continuum approach, and the whole structure is idealized as a shear‐flexural cantilever with rotational spring. The effect of shear and flexural deformation of the wall frame and outrigger trusses are considered and incorporated in the formulation of the governing equations. Geometric nonlinearity in the sense of von Karman is included in the formulation, and Newton–Raphson iterative method is employed to solve the nonlinear equations. A displacement‐based one‐dimensional nonlinear finite element model is developed. Numerical results for wall frame and mega‐column structures with outriggers are obtained and compared with the finite element package MIDAS. The proposed method is found to be simple and efficient, providing reasonably accurate results in early design stages of tall building structures. Copyright © 2011 John Wiley & Sons, Ltd.     

武汉某体育馆大跨度圆钢管拱桁架结构稳定性分析

武汉某体育馆屋盖采用圆钢管拱桁架结构,单榀拱桁架的截面形式为倒三角形,两端支承于立体钢桁架上,该结构的整体稳定性足设计的重点.考虑完善及带缺陷结构两种情况,对单榀及多榀拱桁架子结构进行线性屈曲、几何非线性稳定及弹塑性非线性稳定分析,得到了临界荷载与位移的关系曲线.分析结果表明,初始缺陷及几何非线性对该结构的稳定承载力影响不明显,而材料非线性的影响显著,加强平面外支撑对于提高结构的整体稳定性具有重要作用.     

Nonlinear behavior of prestressed cable trusses

The nonlinear deformational response and stiffness characteristics of four plane prestressed cable trusses subjected to symmetric and asymmetric loads have been examined. The influence of the span-to-sag ratio on the behavior of these structures is also investigated. The method of analysis used is based on an Eulerian formulation which accounts for arbitrarily large joint displacements. The nonlinear effects of member slackening and inelastic material properties are included in the analysis.     

考虑整体稳定的单层网壳截面优化设计

整体稳定性是单层网壳结构设计中的一个关键问题.在进行此类结构的优化时,必须考虑整体稳定性的影响才能得到符合规程要求的设计.本文综合考虑了位移、应力和杆件稳定以及结构整体稳定性条件,提出了基于最优准则法的优化设计方法,可按照钢结构设计规范和网壳结构规程的要求,对单层网壳结构进行杆件截面设计.     

A damage mitigation measure for steel structures under blast loading

The number of explosive attacks on civilian buildings has recently increased and the pattern of damage inflicted on structures when an explosion takes place remains quite difficult to predict. This paper performs a 3-dimensional dynamic response and damage analysis on steel frame structure, subjected to blast loads created by explosive devices. In this study, advantages of using polymer cables as a means of damage mitigation are investigated. Results from this study shows that synthetic fiber ropes as bracing for steel structures reduce the horizontal displacements of structure caused by air blast pressure. The contribution of fiber ropes in structural stability is also presented.     

Ant colony optimisation of spatial steel structures under static and earthquake loading

Optimisation is the process of trying to find out the best possible solution to any problem satisfying constraints. Soft computing is the class of methods which have been inspired by the biological computational methods and nature's problem-solving strategies. Currently, these methods include neural networks, evolutionary computational models such as genetic algorithms, random cost and linguistic models such as fuzzy logic. Ant colony optimisation (ACO) is one such method applied for large engineering combinatorial optimisation problems. A design procedure utilising an ACO technique is developed for discrete optimisation of reticulated steel space trusses. The ACO algorithm is motivated by the analogy with natural phenomena, in particular the ability of a colony of ants to ‘optimise’ their collective endeavours. In this paper, the computational implementation of ACO is presented in a structural design context. The objective function considered is the total weight/cost of the structure subjected to material and performance constraints in the form of stress and deflection limits. In the case of reticulated space trusses, the design variables are the cross-sectional areas of members belonging to various groups. The objective function and constraints are obtained by using structural analysis package FEAST (Anonymous, 1995. FEAST user manual. Trivandrum, India: SEG, SDS Group, ISRO, VSSC) in case of structures subjected to static loading and SAP90 (Anonymous, 1990. SAP90, ETABS, SAFE – computer software for structural and earthquake engineering. Berkeley, CA: Computers and Structures) for earthquake loading for reticulated steel space trusses. The numerical examples presented demonstrate the computational advantage of the ACO for large-scale optimisation problems.     

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.     

天津奥林匹克体育中心游泳跳水馆施工过程分析

天津奥林匹克体育中心游泳跳水馆的屋盖结构体系采用了空间桁架结构。对于空间桁架结构而言,目前多数研究主要集中在节点承载力、静动力性能及其稳定性能上,对于结构施工过程的数值模拟涉及较少。而在大跨度空间钢结构桁架施工过程中,由于结构温度的变化、太阳辐射的影响和卸载方案的差异,施工过程将对结构在使用阶段的力学性能产生显著的影响。以天津奥林匹克体育中心游泳跳水馆钢结构空间桁架结构为工程背景,分析了不同卸载方案、考虑太阳辐射影响的不同合拢温度下钢结构桁架的杆件内力、节点位移、支座反力等结构响应,得出了卸载方案和合拢温度对结构性能的影响程度,为今后大跨度桁架结构的施工方案制定提供了参考和设计依据。     

深圳京基100无线监测数据分析

深圳京基100工程建筑高度达到441.8m,其主体结构主要包括钢筋混凝土核心筒(内含钢骨柱)、巨型钢管混凝土柱组成的巨型钢斜支撑框架、伸臂桁架及腰桁架和钢筋桁架混凝土楼板。该工程结构体系复杂,施工周期长,施工过程受环境影响大。对关键构件进行应力监测,并将监测结果与施工模拟分析结果进行对比分析,及时反馈以保证该复杂工程在施工过程的安全性,为相关工程决策提供依据。     

单层厂房隔震结构弹塑性地震反应分析

由混凝土柱、预应力混凝土屋架或钢屋架组成的横向排架结构是常见的横向受力体系。通过在混凝土柱顶屋架支座处放入隔震器可使混凝土柱的地震反应减小。输入天然地震波对普通结构和隔震结构的弹塑性地震反应进行了计算。结果表明，在地震荷载作用下，隔震结构混凝土柱的水平位移和内力可显著减小。     

平面钢管桁架的面外稳定分析模型研究

受压主管无面外支撑的平面钢管桁架的承载能力主要由其平面外的稳定性控制,而其面外稳定性又主要取决于桁架相贯节点的面外转动刚度。推导K型对称圆钢管相贯节点的面外转动刚度计算公式,进行数值验证,在此基础上建立平面钢管桁架面外稳定分析的杆系有限元模型。进行平面钢管桁架面外稳定性的足尺试验研究,与杆系有限元模型的计算结果进行对比分析。数值分析和试验研究表明:提出的平面钢管桁架的面外稳定分析模型具有较高的计算精度,可以应用于实际工程的分析和设计。     

宁波国际会议展览中心大跨度钢结构设计

宁波国际会议展览中心主展厅大跨度屋盖支承条件复杂，风荷载效应显著。通过风洞试验确定屋盖的风压分布情况，在网壳结构的部分钢管中填充混凝土以平衡部分风吸力。采用抗震球形钢支座克服支座相对位移对屋盖结构产生的影响。小展厅和东、西展厅大跨度屋盖采用了主、次空间管桁架结构体系，在展厅巾部设置了四肢钢管组合柱，从而有效地减小了屋盖的跨度与高度。为了适应大跨度屋面温度变形的要求，采用了滑板式聚四氟乙烯橡胶支座。     

平面拱形桁架等效静风荷载研究

对矢跨比分别为1/4、1/6、1/8的3个拱形屋面进行了同步测压风洞试验,分析风荷载和结构参数对平面拱形桁架风振响应和等效静风荷载的影响规律。风洞试验结果表明, 0°风向时,高矢跨比屋面的最大负压幅值出现在屋顶,而低矢跨比的出现在迎风前缘。从方便工程应用的角度,采用简化振型函数表达针对结构多个位移和杆件应力响应的多目标等效静风荷载。在工程常用范围内,分析结构矢跨比、跨度、屋面质量、设计风速和风向等参数对中部和端部平面拱形桁架多目标等效静风荷载的影响,得到可用于指导该类结构抗风设计的等效静风荷载风压系数建议值,且经校核,在该等效静风荷载作用下的结构响应与实际动力响应极值吻合较好。     

Shaking table model tests on a complex high‐rise building with two towers of different height connected by trusses

The past decades have witnessed a flourish of novel high‐rise structures throughout the world under the requirement of a ceaselessly progressing architectural aesthetics, resulting in a complex plan and elevation of a building. Shanghai International Design Center is such a high‐rise building with two towers of different heights connected by trusses, and the structural system is composed of steel frame, reinforced concrete (RC) core wall and shear walls. The great irregularity in plan and elevation, according to Chinese code, necessitates a detailed study, which usually includes refined structural analysis, scaled structural model test and large size member or joint test. As recommended by the peer review committee, the shaking table tests of the 1:15‐scale structural model were performed. Based on the analysis and shaking table model testing, it was found that the stiffness of the connecting trusses is capable of coordinating the two towers to resist lateral forces jointly even under strong earthquakes. As a result of stiffening action brought by the connecting trusses, whipping‐lash effect in longitudinal direction develops sharply on top storeys. Structural responses at storeys around the connecting trusses vary remarkably due to sudden change in lateral stiffness. Through comparison between tests and numerical analysis, weak positions of the structure are identified, and some corresponding measures for improving the design of this structure are also put forward. Copyright © 2008 John Wiley & Sons, Ltd.     

空间支撑钢框架结构的三重非线性分析

为了探讨三维结构的高等分析方法,本文将有限单元法与梁柱法相结合,建立了空间支撑钢框架结构的三重非线性分析方法,该法综合考虑了几何、材料和连接非线性效应。文中基于非线性连续介质力学理论和考虑剪切效应的稳定插值函数建立的严格三维梁柱单元刚度矩阵,包含了轴向、剪切、双向弯曲与扭转及其各耦合效应。三维单元简化塑性区模型可模拟塑性扩展,利用单元两端抗转弹簧和考虑支撑效应的节点域剪切变形模型来模拟连接非线性。使用包括几何、材料和连接非线性的数值算例来检验本文方法和所编计算机程序的可行性、有效性与精确度。算例表明,利用本文方法,每个构件只需一个单元即可准确预测三维结构的极限荷载与失稳模态,可提高结构非线性空间性能的分析效率。     

Application and development of modern long-span space structures in China

Modern long-span space structures, developed during the 1970s and 1980s, are light and effective structures based on new technologies and light-weight high-strength materials, such as membranes and steel cables. These structures include air-supported membrane structures, cable-membrane structures, cable truss structures, beam string structures, suspen-domes, cable domes, composite structures of cable dome and single-layer lattice shell, Tensairity structures and so forth. For the premodern space structures widely used since the mid-twentieth century (such as thin shells, space trusses, lattice shells and ordinary cable structures), new space structures have been developed by the combination of different structural forms and materials. The application of prestressing technology and the innovation of structural concepts and configurations are also associated with modern space structures, including composite space trusses, open-web grid structures, polyhedron space frame structures, partial double-layer lattice shells, cable-stayed grid structures, tree-type structures, prestressed segmental steel structures and so forth. This paper provides a review of the structural characteristics and practical applications in China of modern rigid space structures, modern flexible space structures and modern rigid-flexible combined space structures.     

上承式装配式公路钢桥悬臂推出法架设过程中稳定性研究

结合一座上承式装配式公路钢桥在采用悬臂推出法架设过程中发生的事故案例,基于钢结构弯扭屈曲理论,分析其失稳破坏机理,并通过有限元数值模拟技术,对架设过程中不同状态进行屈曲分析。计算结果表明:如果导梁桁架横向间距过小,即使在导梁搭上对岸摇滚后,仍有可能因为发生弯扭屈曲失稳而导致整个桥梁倒塌;增大导梁桁架横向间距能有效提高导梁结构的抗屈曲稳定承载力。     

南亚之门塔楼结构初步设计

南亚之门工程位于云南省昆明市,塔楼建筑高度366m,为我国目前8度地区拟建的超高建筑之一。采用巨型框架-混凝土核心筒结构体系,层23以下建筑平面呈正方形,层23以上削角,建筑平面呈逐渐缩小的八边形,并在建筑顶部形成与底部旋转45°的内接正方形平面。置于平面四角的巨柱在层23一分为二形成8根倾斜角柱,并在设备层设置环带桁架,与巨柱形成抗侧刚度较大的巨型框架,与核心筒一起承担地震作用。环带桁架与核心筒通过加强层的楼板协调变形,起到"虚拟伸臂"的作用。采用速度型粘滞阻尼器增加结构阻尼,以减小地震作用。