Comparative study of special and ordinary braced frames

The collapse probability of ductile and non‐ductile concentrically braced frames was investigated using nonlinear dynamic response analysis. Two buildings with three and nine stories located in Boston and Los Angeles, respectively, were designed and subjected to ground motions from the areas. In Boston area, three‐story and nine‐story buildings were designed as ordinary concentrically braced frame with response modification reduction factor R equal to 3 1/4 to be considered as non‐ductile structural systems; comparatively, in Los Angeles area, three‐story and nine‐story buildings were designed as special concentrically braced frame with response modification reduction factor R equal to 6 to be considered as ductile structural systems. In order to evaluate the performance of ductile and non‐ductile concentrically braced frames in moderate and severe seismic regions, ATC‐63 would be used as reference to assess the seismic behaviors. Evaluation approach recommended by ATC‐63 was adopted, and hundreds of nonlinear dynamic analyses were performed. Through alternating the scale factors of designated ground motions, median of structural collapse intensity was presented for each structure. By observing the results of statistical performance assessment, the seismic performance of the systems was evaluated, and some observations are made based on the study. Copyright © 2012 John Wiley & Sons, Ltd.     

盖板型钢框架刚性节点延性性能试验研究

针对钢框架梁柱栓焊混合刚性节点易出现的焊缝脆性破坏形式及其机理,对节点构造设计提出了改进意见,即在节点位置加焊楔形盖板。通过足尺低周往复荷载试验,得到了较为饱满的滞回曲线,验证了盖板型刚性节点具有良好的延性性能并能够在设计位置出现塑性铰。对盖板型与常用型节点进行了比较,量化了盖板型节点承载能力及延性性能的优势。提出了防止节点脆性破坏的构造改进措施。     

Reliability analysis of frame structures with brittle components

A review is provided of the recent developments in the reliability analysis of ductile (elastic-plastic) systems and of the stable configuration approach of structural system reliability analysis. These are combined to obtain a methodology for evaluating the reliability of frames that have primarily ductile components but also a few brittle components. The methodology is applied to two frame structures.     

Ductility failure criterion for infilled-wall frame structures

填充墙框架结构与纯框架结构抗震性能差异显著，建立填充墙框架结构的破坏准则，有助于揭示填充墙破坏对结构整体性能的影响规律，阐明其性能退化机理。为此，对14组共59榀不开洞填充墙框架模型的变形能力和承载力对结构性能退化的影响规律进行研究，得到破坏过程中框架柱、填充墙及整体性能退化之间的量化关系，进而提出不开洞填充墙框架的延性破坏准则和性能评价标准。研究结果表明：填充墙框架模型对应延性准则的破坏指数平均值在0.724~0.928之间，延性准则能够实现填充墙框架结构倒塌破坏的量化表征；综合6组19榀填充墙框架的试验现象、性能退化特点和破坏指数统计结果，建议中等破坏和严重破坏临界点破坏指数分别取0.1和0.4，延性准则可用于填充墙框架结构的抗震性能研究和倒塌破坏评估。     

填充墙框架结构延性破坏准则

填充墙框架结构与纯框架结构抗震性能差异显著,建立填充墙框架结构的破坏准则,有助于揭示填充墙破坏对结构整体性能的影响规律,阐明其性能退化机理。为此,对14组共59榀不开洞填充墙框架模型的变形能力和承载力对结构性能退化的影响规律进行研究,得到破坏过程中框架柱、填充墙及整体性能退化之间的量化关系,进而提出不开洞填充墙框架的延性破坏准则和性能评价标准。研究结果表明：填充墙框架模型对应延性准则的破坏指数平均值在0.724～0.928之间,延性准则能够实现填充墙框架结构倒塌破坏的量化表征;综合6组19榀填充墙框架的试验现象、性能退化特点和破坏指数统计结果,建议中等破坏和严重破坏临界点破坏指数分别取0.1和0.4,延性准则可用于填充墙框架结构的抗震性能研究和倒塌破坏评估。     

Seismic design and assessment for midrise buildings equipped with damped-outrigger system

The damped-outrigger system has been proposed to improve the performance of conventional outrigger systems in controlling the structural seismic response by increasing the damping and stiffness. The purpose of this study is to demonstrate the effectiveness of using damped-outrigger systems in midrise buildings and provide engineers with a comparison between conventional structural systems such as moment resisting frame (MRF) and buckling-restrained braced frame (BRBF) in proposing the most suitable structural system. In this study, the buckling-restrained brace and viscous damper are adopted as the energy dissipation devices in the damped-outrigger system. A total of 48 midrise numerical models with various building heights and structural systems are analyzed using nonlinear response history analysis and incremental dynamic analyses. The analysis results show that the midrise buildings equipped with a damped-outrigger system with either viscous damper or buckling-restrained brace (BRB) can reach similar and even better seismic performance when compared with the BRBF; it also reduces the structural responses by around 30% for the maximum roof drift and acceleration responses when compared with MRF. The analysis results could provide a reference for structural engineers when selecting suitable lateral force resisting systems for midrise buildings.     

System reliability of timber structures with ductile behaviour

The present paper considers the evaluation of timber structures with the focus on robustness due to connection ductility. The robustness analysis is based on the structural reliability framework applied to a simplified mechanical system. The structural timber system is depicted as a parallel system. An evaluation method of the ductile behaviour is introduced. For different ductile behaviours, the system reliability is estimated based on Monte Carlo simulation. A correlation between the strength of the structural elements is introduced. The results indicate that the reliability of a structural timber system can be significantly increased due to the ductile behavior.     

Buckling restrained braces as structural fuses for the seismic retrofit of reinforced concrete bridge bents

A structural fuse concept is proposed in which easily replaceable ductile structural steel elements are added to an RC bridge bent to increase its strength and stiffness, and also designed to sustain the seismic demand and dissipate all the seismic energy through hysteretic behavior of the fuses, while keeping the RC bridge piers elastic. While this concept could be implemented in both new and existing bridges, the focus here is on the retrofit of non-ductile reinforced concrete bridge bents. Several types of structural fuses can be used and implemented in bridges; the focus in this paper is on using Buckling Restrained Braces (BRB) for the retrofit of RC bridge bents. The results of a parametric formulation conducted introducing key parameters for the design procedure of the fuse system, validated by nonlinear time history analyses are presented. A proposed design procedure, using BRBs as metallic structural fuses, is found to be sufficiently reliable to design structural fuse systems with satisfactory seismic performance. A graphical representation to help find admissible solutions is used, and shows that the region of admissible solution decreases when the frame strength ratio increases as a larger fuse element is required to achieve an effective structural fuse concept.     

高层建筑斜交网格筒体结构分析与研究

斜交网格筒体结构体系是一种新颖的结构形式,可以实现建筑立面的多样性,同时,该体系在受力方面也具有一些与传统框筒体系不同的特点。本文采用标准算例,详细比较了斜交网格筒体结构体系与密柱深梁框筒结构体系在重力荷载、水平荷载作用下的差异,说明了斜交网格筒体结构在应用于高层建筑结构设计中,需要注意的一些关键问题,从而为进一步推广该体系的应用提供参考。     

Probabilistic safety assessment of self-centering steel braced frame

The main drawback of conventional braced frames is implicitly accepting structural damage under the design earthquake load, which leads to considerable economic losses. Controlled rocking self-centering system as a modern low-damage system is capable of minimizing the drawbacks of conventional braced frames. This paper quantifies main limit states and investigates the seismic performance of self-centering braced frame using a Probabilistic Safety Assessment procedure. Margin of safety, confidence level, and mean annual frequency of the self-centering archetypes for their main limit states, including PT yield, fuse fracture, and global collapse, are established and are compared with their acceptance criteria. Considering incorporating aleatory and epistemic uncertainties, the efficiency of the system is examined. Results of the investigation indicate that the design of low- and mid-rise self-centering archetypes could provide the adequate margin of safety against exceeding the undesirable limit-states.     

端部配置延性铸造件的装配式防屈曲支撑抗震性能试验研究

中心支撑钢框架结构(CBFs)中支撑与框架梁柱连接时,采用传统焊接连接方式容易发生脆性破坏,使支撑不能发挥应有的作用.为此,设计了一种可与框架结构采用螺栓连接的端部配置延性铸造件的装配式防屈曲支撑,并对6个支撑完成了低周往复加载试验,研究了其破坏模式、应力分布、滞回性能等.结果 表明,端部配置延性铸造件的装配式防屈曲支...     

支撑和节点板延性性能的抗震设计

介绍钢结构铰接框架-支撑体系中支撑和节点板的震害、实验室的抗震性能研究、有关规范的规定和具有延性性能的支撑和节点板的设计概念及方法。由于我国现行建筑抗震规范中尚不包括钢结构铰接框架-支撑体系,故文中提出的抗震设计原则、规范规定和计算公式,可供从事钢结构设计和研究的技术人员参考。     

A new high performance semi-active bracing system

Structural control under seismic excitation is becoming an important problem in earthquake engineering. Among several control systems, semi-active control is usually possible and efficient. In the conventional bracing systems it is assumed that the braces buckle under little compressive forces. In this research a semi-active on–off brace strategy is implemented to improve the conventional braces performance. A new completely tensile ribbed bracing system (RBS) has been developed to use the whole capacity of the member. In the proposed system the buckling of compressive member is prevented using a ribbed shape cylinder. RBS causes a permanent-stiffness-presence system that leads to less structural responses. The permanent deflections are removed at the end of excitations by a length correction control system. In this mechanism there is no need for any actuator and large power supply, but just a battery-sized power supply to switch the ribbed mechanical system on or off. The developed mechanism is composed of a ribbed supplemental part and a normal wind-bracing on each floor. Despite the fact that this system does not get control command from outside, it is called a semi-active control system. The hysteresis loop of the braces is similar to ductile tensile steel members. Therefore the system is full capacity design. Nonlinear dynamic analysis of the system has been carried out and its structural behaviour has been investigated. Also damage indices are determined in order to compare the RBS with the conventional bracing systems.     

延性节点钢框架结构的抗震性能分析

为简化延性耗能节点钢框架结构的数值计算,利用延性耗能节点简化理论模型分别对6层、12层的翼缘削弱型节点钢框架和盖板加强型节点钢框架进行简化,并对框架简化模型和实际框架模型进行模态分析;提取框架结构的前3阶基本周期并计算阻尼比,并对框架结构简化模型和实际模型开展El Centro波和Taft波2种地震波下的动力时程分析,将框架简化模型计算得到的框架基本周期、柱顶位移和柱底剪力时程曲线与实际框架模型的数值计算结果进行对比。结果表明:整体上框架简化模型和实际框架模型的数值计算结果吻合较好,翼缘削弱型节点框架简化模型计算的框架基本周期比实际模型计算值稍小,相对误差在8.5%以内,而盖板加强型节点框架简化模型计算的框架基本周期比实际模型计算值稍大,相对误差在4.0%以内;柱顶位移和柱底剪力时程曲线吻合较好。延性节点简化理论模型用于框架结构动力计算具有极高的计算精度,可有效分析延性节点钢框架结构的抗震性能。     

Seismic response of shallow-floor buildings

A framing system considered for a shallow-floor building to be used in seismic zones has wide shallow beams with sufficient stirrups. Two-way slab design is used for this system. This shallow-floor system is likely to have good ductile behavior as the beams deform inelastically. The lateral resisting system is designed with a ‘strong column—weak beam’ ductile frame configuration so that the hinging zones occur within the beams away from the face of the column. The beams will be substantially wider than the columns. The joint and hinge regions must have sufficient tie and stirrup reinforcement. P-delta effects should be considered but are not serious when drifts are controlled. The survivability of the ductile shallow-floor building under moderate earthquakes is studied. The serviceability, e.g., story drift, of the building is of concern. The usual case is that the building is likely to satisfy code requirements for base shear resistance and corresponding story drift limitation. Contrary to code prediction, the performance under a moderate earthquake often yields large story drifts which may severely damage the non-structural systems.     

Structural fire performance of earthquake-resistant composite steel–concrete frames

Seismic and fire design of a building structure may be two very demanding tasks, especially if included in a performance based design philosophy. For the time being, the necessary harmonization on the regulations concerning these two design fields is almost missing, thus preventing the effective possibility of an integrated design. Besides, while many countries have already moved towards the use of performance-based codes for seismic design, the application of such methodologies for the fire design of structures is still limited in scope. Within this framework, the development of suitable procedures introducing structural fire performance issues for a comprehensive design methodology is needed.In this paper, a numerical investigation for the assessment of the structural fire performance of earthquake resistant composite steel–concrete frames is presented. With reference to a case study defined in the framework of a European Research Project, a great effort was devoted to the identification of the key structural parameters allowing for a possible correlation between the predictable performances under seismic and fire loadings, when these two are considered as independent actions.At the conceptual design level, the most suitable structural solution with respect to both design actions was chosen, including composite beams and circular steel concrete-filled columns. The frame was designed in order to resist severe seismic action according to the ductile design approach provided by Eurocode 8; the parameters affecting members’ sizing were outlined in this phase. Afterwards, the seismic performance of the designed frame was investigated by means of non-linear static analyses; once the seismic performance objectives were met, in order to evaluate the structural fire performance of the whole frame a set of criteria was defined. To this purpose, thermo-mechanical analyses under different boundary conditions were developed and in order to identify the possible mechanisms leading to structural failure, the state of stress at the critical cross-sections at different times of fire exposure was investigated. Another point of main concern was represented by the assessment of the influence of different restraining conditions on the achieved fire resistance rating and kind of structural failure.Moreover, the proposed methodology allowed making an estimate of the amount of axial restraint provided to the heated beams by the surrounding structure; in this view, the importance of choosing column elements in function of their flexural stiffness was revealed, in order to correlate it with the predictable performances under both seismic and fire loadings.     

超限复杂高层武汉中心的结构抗震分析

介绍了在进行武汉中心的结构抗震分析与设计中,对平面及竖向均不规则的超高层结构抗震分析时注意的要点.武汉中心总高438 m,高宽比7.88.为了配合建筑内部使用需要,武汉中心采用的的抗侧力体系,在66层以下采用巨柱框架—核心筒—伸臂桁架结构体系,其上收掉中间的8根框架柱.在满足结构整体稳定、规范规定的层间位移角限值以及墙体轴压比限值的条件下,在结构底部采用内置钢板剪力墙以尽量减小墙体厚度.同时调整了外框架的结构形式以同时满足建筑的需求和外框架承担地震剪力的最小比例.设定了主要抗侧力构件的性能目标以保证结构抗侧力构件在中震和大震下达到预期性能.     

珠江新城某超高层住宅结构设计

针对广州珠江新城某超限高层住宅钢筋混凝土剪力墙结构设计进行探讨研究,介绍了该项目结构体系、工程超限情况及改进加强措施,并进行了整体结构分析、中震不屈服分析,以及PKPM静力弹塑性分析,计算结果表明结构在罕遇地震下处于延性阶段,结构抗震性能满足规范要求。     

Ductile moment-resisting frames using cold-formed steel sections: An analytical investigation

This paper presents an investigation on the potential use of cold-formed steel sections (CFS sections) in moment-resisting frames (MRFs) for seismic applications. The main limitation of CFS sections is the low out-of-plane stiffness of their thin-walled elements which leads to low ductility. The main components of MRFs are beams, beam-column connections and columns. In earthquake resistant MRFs, the beams are designed to provide considerable ductility, whereas the other elements are mainly limited to their elastic range. The performance of a new shape of CFS beam with curved flange is examined analytically and compared with that of conventional shapes. The proposed beam-column connections include through plates which potentially limit the out-of-plane action of the forces transferred through the connections. The behaviour of both individual CFS beam sections and CFS beam-column connections is studied by means of finite element analysis (FEA). The results of the analyses show that the new beam cross sections and connections exhibit a good ductile behaviour, something which cannot be achieved by conventional cold-formed frame elements.     

半刚性框架-无黏结十字加劲钢板剪力墙结构低周往复荷载试验研究

通过对一榀几何比例为1∶3的两层单跨半刚性框架-无黏结十字加劲钢板剪力墙结构在低周往复水平荷载作用下的试验研究，得到了循环荷载下结构的滞回曲线及各关键部位的受力变形情况。分析其承载能力、破坏形式、耗能能力、刚度退化、承载力退化、延性等指标。在此基础上，分析了无黏结十字加劲内嵌钢板与半刚性框架的相互作用。结果表明：该结构具有良好的延性和耗能能力，安全储备高；半刚性框架与内嵌钢板协同工作良好；无黏结加劲构件的设计避免了焊缝的应力集中，降低了钢板墙在加工过程中对工艺的要求；加劲构件的设置改善了钢板墙的受力模式，提高了钢板墙体系的承载力及刚度，减轻了滞回曲线的“捏缩”现象。研究结果可为半刚性框架-无黏结十字加劲钢板剪力墙结构进一步的工程应用和理论研究提供参考。