Multihazard fragility assessment of steel‐concrete composite frame structures with buckling‐restrained braces subjected to combined earthquake and wind

Engineering structures may inevitably be subjected to multiple natural hazards (such as earthquakes and winds) during their life cycles. This paper presents an efficient multihazard fragility methodology based on the structural demand models. The approach is applied to two steel‐concrete composite frame structures (SCCFSs), with and without buckling‐restrained braces (BRBs), aiming to evaluate the effect of BRBs on controlling the structural responses and fragilities under the combined earthquake and wind loads. In total, 120 earthquake records are selected, and 120 sets of wind drag force time histories are simulated by considering the spatial variation along the height of the exemplar building. The combined “earthquake–wind” events are stochastically assembled, in which the intensities of these two hazards are modeled using the Monte Carlo simulation. The OpenSees platform is employed to calculate the dynamic responses of the SCCFSs with and without BRBs under simultaneous earthquake and wind loads. The goodness of fits of the first‐, second‐, and third‐order polynomial in predicting the structural demand are evaluated, and the optimal polynomial is employed to generate the multihazard fragility surfaces at different damage states. The numerical results indicate that the structural responses and fragilities under the combined earthquake and wind are higher than those under an individual hazard, while the influencing extent varies with the relative intensities of these two hazards. The impact of multiple hazards and the control effect of BRBs on the structural responses and fragilities are systematically quantified and discussed in details.     

悬挑长度12m钢桁架雨篷的结构方案比较

钢结构因其特有的自重轻、相对刚度大、受力计算分析准确、生产加工方便等优势而被广泛应用在大型建筑和重要的结构部位。钢桁架是钢结构中一个重要构件之一,特别适用于跨度或高度较大的结构,如桥梁和大跨度屋盖结构等。本工程合理地采用钢桁架做悬挑长度为12 m雨篷的受力构件,并进行两种结构方案的受力分析比较,选择了安全、受力合理的结构方案,希望能给广大设计同仁带来裨益。     

某钢结构厂房金属拱形屋面倒塌分析

通过对某钢结构厂房的金属波纹屋盖遇大风后倒塌事故的处理，较详细地分析了其原因，并对类似屋盖结构的应用以及特殊地段风荷载的取值提出了建议，以保证屋面的正常安全使闸。     

昆明南部汽车客运站钢结构设计

昆明南部汽车客运站是面向东南亚的枢纽客运站,站房主体为钢框架,屋面结构采用支承在柱顶树形支撑上的空间管桁架,造型新颖。针对该工程的特点,从结构体系、抗震分析、节点构造等方面进行详细介绍,重点分析了主体结构和屋面结构的相互作用、风荷载对大跨度屋面结构的影响。     

Behavior and design of reinforced concrete frames retrofitted with steel bracing against progressive collapse

Steel bracing is able to improve progressive collapse resistance of reinforced concrete (RC) frames, but the bracing design is typically based on seismic retrofitting or lateral stability. There is no approach for design of steel bracing against progressive collapse. To this end, a retrofitting approach with steel braces is proposed based on analysis of macro finite element (FE) models with fiber beam elements. The FE models were initially validated through the experimental results of a braced frame and then used to investigate the effects of pertinent parameters on the progressive collapse resistance of planar frames. The results suggest the braces should be placed at the top story. Thereafter, macro FE models are built to investigate the dynamic responses of the three‐dimensional prototype RC frames under different column removal scenarios (CRS) and show the necessity of retrofitting. Accordingly, the design approach of steel bracing is proposed with incremental dynamic analysis (IDA) and assuming independent contribution of braces and frames to resistance. Finally, the fragility analysis of the frames under a corner‐penultimate‐exterior CRS is conducted through IDA and Monte Carlo simulation, and the results confirm the validity of the proposed design approach for retrofitting RC frames.     

基于一致倒塌风险的建筑抗震评价方法研究

建筑结构的抗震能力、尤其是抗倒塌能力设计目标应根据其所在场地未来一定设计使用年限内可能遭遇的地震危险性来设定。首先介绍了基于动力增量分析（IDA）的结构倒塌易损性分析方法,随后结合地震危险性分析,分别给出了结构抗倒塌能力和结构所面临地震危险性的概率模型,进而根据结构在未来一定设计使用年限内的倒塌概率,对建筑结构的抗地震倒塌风险进行定量评价,并给出了相应的计算方法。以一座7度抗震设防的RC框架结构为例,计算了该RC框架结构在3个同为7度抗震设防而地震危险性不同地区的地震倒塌风险,指出仅以抗震设防烈度作为建筑结构抗震设计的依据所存在的不足,建议应基于一致倒塌风险进行结构抗震设计,并提出了相关结构抗震设计方法需开展的研究工作。     

新型轻钢龙骨体系水平位移有限元分析方法

无比钢结构是一种新型的轻钢龙骨体系,我国现有的结构软件无法直接对其进行设计和计算,采用有限元方法是目前进行结构分析较好的选择。介绍了无比钢结构的组成及做法,提出了整体结构的有限元建模方法,并以5层教学楼为例,采用ABAQUS软件包分析了结构在风载和地震荷载作用下的水平位移,且与规范要求的最大值进行了比较。结果表明,按所提出的针对无比钢结构的有限元建模和分析方法,在风载和地震作用下计算得到的多层无比钢结构的层间和顶点水平位移均可以满足规范要求。     

Structural design of high‐rise buildings using steel‐framed modules: A case study in Hong Kong

Steel‐framed modular buildings afford certain advantages, such as rapid and high‐quality construction. However, although steel‐framed modules have been adopted in several countries, most of them are limited to low‐to‐medium‐rise structures; modular high‐rise buildings are rare. This study proposes a feasible structural design solution for high‐rise buildings using a steel‐framed modular system. A 31‐story student hostel building in Hong Kong is redesigned as a steel‐framed modular building and used as a case study. The finite element models of the building are formulated, and the structural behaviors under wind and earthquake load scenarios are compared. Moreover, the structural design process used for the 31‐story building is applied to design a hypothetical 40‐story modular building to further examine the proposed design solution. The numerical analysis results indicate that the roof lateral displacements and interstory drift ratios of the redesigned modular building are within the allowable limits of design codes; moreover, the modular connections behave elastically under the most adverse loading scenarios. Accordingly, the proposed solution can be used to design steel‐framed modular buildings of up to 40 stories, while complying with relevant wind and seismic codes.     

中美风荷载规范在电站锅炉钢结构上的应用

主要研究大型锅炉钢结构的风荷载,采用中国GB/T 22395—2008《锅炉钢结构设计规范》和美国UBC 97以及ASCE 7规范对大型锅炉钢结构进行静力分析的方法。阐述两国规范风荷载的规定在锅炉钢结构设计上的应用,以及风荷载各规范之间的转换,并对3个规范的风荷载计算方法进行比较。通过一工程实例,将风荷载与垂直荷载按相关规范计算并进行组合,加载到钢架上,用大型结构分析程序STAAD V8i进行结构的空间结构分析,求解出结构的水平反力和位移以及主要构件的内力和应力比。     

Performance-based seismic fragility analysis of retaining walls based on the probability density evolution method

Seismic fragility analysis is an efficient way to study the seismic behaviour and performance of structures under the excitation of earthquakes of varying intensity, and an essential part of the seismic risk assessment of structures. A recently developed dynamic reliability methodology, the probability density evolution method (PDEM), is proposed for the dynamic reliability and seismic fragility analysis of a retaining wall. The PDEM can obtain an instantaneous probability density function of the seismic responses and easily acquire the seismic reliability of the structural system. An important advantage of the PDEM is its high efficiency relative to that of the Monte Carlo simulation method, which is often used in the reliability and fragility analysis of structures. The present study uses a typical gravity retaining wall to illustrate stochastic seismic responses and fragility curves that can be obtained by the PDEM. The combined uncertainties of the seismic force and soil properties are explicitly and systematically modelled by stochastic ground motions and random variables respectively. The performance of the retaining wall is analysed for different acceptable levels of backfill settlement. Additionally, seismic fragility curves are constructed without assuming the distribution of the seismic response.     

Experimental investigation of composite steel plate deep beam infill steel frame

Steel frame and shear wall infill steel frame are two commonly lateral load resisting systems used in building structures. To realize the modulation of initial stiffness of steel structures, make it easily assembled and removed and prevent plastic hinges developing in the frame columns and collapse of all structure, a new anti-seismic infill wall system, composite steel plate deep beam (CDB), is introduced. The system uses steel plate deep beam with a precast reinforced concrete panel attached one side. This paper describes the experimental work related to the tests of CDB under cyclic loads. The experimental results of one pure steel frame (PF) and two composite steel plate deep beam infill steel frame (CDBF) with different span-height ratio are summarized and discussed, the hysteretic loops were obtained. Based on the test results, effects of the CDB on the load capacity, ductility, hysteretic property and energy-dissipation of the pure steel frame were analyzed. The results show that the CDB enhances the initial stiffness and load capacity by a large margin, and the hysteretic loops are replete and the skeleton curves have apparent stage of plastic flow, the ductility and energy dissipation capacity of the test specimens are enhanced. Lastly, regression analysis based on the tests data, and restoring force model can apply to elastoplastic response analysis of the CDBF systems. Therefore, the deep beam can be used as the first defense line of earthquake-resistance, and the steel frame can be used as the second.     

Disproportionate collapse analysis of cable-stayed steel roofs for cable loss

Disproportionate collapse has been identified lately as a real cause of failure for structural engineering projects. Rare and unexpected, the phenomenon of disproportionate collapse usually results to many fatalities and thus, its analysis and mitigation is deemed necessary. This work describes the analysis of a cable-stayed steel roof under the scenario of a cable loss. The event of a cable loss is assumed to be brittle, while relevant recent recommendations suggest the application of a scaled equivalent static force at the points of the anchorage of the cable but in the opposite direction of the original cable force. In this paper, three different conditions have been considered in order to study the effect of the cable loss into the overall structural response of a typical cable-stayed roof; the level of the equivalent nodal load in the opposite direction of the original cable force varies. The steel structure of the roof, in its complexity, closer to responding as a cable-stayed bridge rather than a steel roof provides a useful template for conclusions; several topics regarding disproportionate collapse and cable losses are discussed.     

大连国际会议中心结构设计研究综述

大连国际会议中心工程以16个内藏钢桁架的钢筋混凝土交通筒体构成整个建筑物的竖向承重和水平抗侧力结构。在标高15.3m处支撑起钢桁架构成主要使用功能钢平台,建筑中部设置1 700座歌剧院,在钢平台外边缘悬挑部位有7个500人以上会议厅。13个交通筒上部设置15个屋盖支撑点,形成不规则大跨悬挑屋盖。曲面外围护框架结构与屋盖、悬挑钢平台相连,构成空间组合结构,共同抵御地震、温度和风荷载作用。采用性能化设计方法和目标,并提出相应计算方案、设计原则、试验要求,保证整体设计的有序和有效性。     

A Monte Carlo based method for the dynamic “fragility analysis” of tall buildings under turbulent wind loading

This paper presents a numerical algorithm for the simulation of the along-wind dynamic response of tall buildings under turbulent winds, using Monte Carlo (MC) integration methods. The proposed MC numerical procedure was used to compute the power spectral density of the buffeting loads, and to derive the statistics of the dynamic response in the presence of uncertainty in the wind loading. The CAARC prototype building was utilized to validate the proposed algorithm. This paper also presents the computation of the structural fragility curves of the CAARC building under extreme winds; preliminary investigations were conducted to assess the applicability of the proposed algorithm to a performance-based assessment.The results of these studies validated the appropriateness of the developed algorithm through comparison to reference values obtained from the literature for the CAARC building. Furthermore, structural “fragility curves” were utilized for a preliminary performance analysis, based on simulated along-wind response serviceability limit states.     

某会所结构设计与分析

某会所为地上2层、地下1层的坡屋面框架结构,通过设置变形缝,结合建筑立面要求优化结构的布置,并采取合理的构造措施,使结构计算结果符合规范要求.该工程大部分屋盖采用钢结构,根据建筑坡屋面造型采用相贯节点圆钢管桁架和H型钢梁相结合的结构体系,不仅与建筑形态吻合,而且结构受力合理.通过整体分析和对屋盖钢结构的有限元分析表明,结构具有良好的安全性和经济性.     

火灾下门式钢刚架倒塌试验与雷达位移测试系统有效性研究

近年来火灾下钢结构倒塌造成消防官兵伤亡的事故频繁发生,亟需开展建筑火灾倒塌预警研究.现有研究已表明:可以通过测量门式钢刚架柱顶和屋脊处的微变形来预测火灾下结构的倒塌,但由于高温和热烟气的存在,火灾下位移的实时测量问题尚需研究.该文通过试验方法研究雷达在实际火场位移测量中的可行性,首先设计一个缩尺单跨门式钢刚架的火灾试验...     

济南唐冶新区体育中心屋盖桁架结构设计与分析

济南唐冶新区体育中心主体结构采用混凝土结构,屋盖和墙面支撑体系采用钢结构。对屋盖桁架结构设计中风荷载的取值、屋盖结构的强度、刚度和稳定性分析、主要构件的计算等方面做了深入的工作。对大直径钢管汇交处的节点进行了设计,提出相关连接方式。对结构分缝提出了在连接板开椭圆孔的构造方法,可为此类桁架结构的设计与优化提供参考。     

飓风作用下某大跨体育馆屋盖的结构选型分析

菲律宾某地最大设计风速达到215 km/h,风力17级,属于飓风,因此大跨屋盖的结构设计异常困难。该地的某大跨体育馆的下层屋盖为游泳馆屋盖,并作为上层屋盖的支承点和看台;上层屋盖为大跨度空间钢桁架结构,屋盖东西长为130.0 m,南北宽为31.0 m。考虑屋盖跨度大、整体结构超长的特点,上层屋盖采用平面管桁架形式,下侧游泳馆屋面及看台采用空间三角管桁架结构。基于屋盖结构方案的可行性比选,选取普通框架管桁架结构、斜拉空间桁架、斜拉空间桁架加配重3种方案,进行结构整体建模的非线性分析,比较整体结构的挠度、构件规格、结构用材以及可施工性。分析认为,结构方案3具有较好的经济性和结构性能,比较适用于考虑飓风作用下大跨空间结构的结构形式。     

地震作用下钢框架结构抗竖向连续倒塌可靠度分析

为了对偶然荷载作用下结构的抗连续性倒塌进行可靠度研究,采用OpenSEES软件建立钢框架连续倒塌分析数值模型,考虑到钢框架结构材料和荷载的不确定性,使用拉丁超立方抽样方法生成钢框架结构随机样本,并采用随机Pushover算法对钢框架结构进行分析,计算得到X、Y两个方向不同地震水平下各钢柱承载能力及变形能力的可靠度指标,根据抗震可靠度相关理论确定目标可靠度指标,通过比较各柱的可靠度指标和目标可靠度,对结构在地震作用下最可能失效构件进行识别。基于所识别的最可能失效构件,结合所生成的100组钢框架结构随机样本,采用拆除构件法对钢框架结构在单柱失效和多柱失效等工况下进行抗连续倒塌IDA分析,得到随机IDA分析曲线。通过结构连续倒塌极限状态方程,计算得到损伤结构发生连续倒塌的概率及连续倒塌条件可靠度指标。采用基于风险的结构连续倒塌概率表达式,分析地震作用下钢框架结构发生局部破坏后的连续倒塌全概率可靠度,为准确评价钢框架结构在地震作用下的抗连续倒塌能力提供依据。     

大连国际会议中心新型节点设计与试验研究

大连国际会议中心外围护结构的曲面框架通过不同节点方式与屋架、钢平台连接,形成复杂空间整体组合结构。由于建筑物外形设计的多样性,曲面框架本身的形状、边界条件和构造存在相当大的差异。研究了曲面外围护框架中落地部分框架与钢平台的连接节点。这部分框架柱三向倾斜,框架柱面外的无支长度最长超过70m,最短也有60m。由于曲面外围护框架面外刚度薄弱,需要与内部钢平台、屋架拉结,形成空间结构。这种拉结节点的构造要求应考虑曲面框架柱自身的承载能力、连接节点传递力的途径以及相应节点约束控制,达到整体设计要求。