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.     

斜隅支撑钢框架体系的隅撑位置分析

斜隅支撑框架体系(KBF)是一种新型消能支撑框架钢结构体系,它具有延性好、抗侧移刚度大、震后容易修复的特点。结构主要构件在隅撑的保护下即使受到罕遇地震荷载作用也不易受到损伤。本文针对隅撑的安装位置并且运用有限元方法对其进行弹塑性加载分析,总结出一些结论和设计建议。     

斜隅支撑框架体系的弹塑性受力分析

斜隅支撑框架体系(KBF)是一种新型耗能支撑框架钢结构体系,它具有延性好、抗侧移刚度大、震后容易修复的特点。结构主要构件在隅撑的保护下即使受到罕遇地震荷载作用也不易受到损伤。为此采用有限元方法(FEM)对此类结构进行了系统的弹塑性受力分析,全面总结了其抗侧移受力性能与各结构参数间的关系,并总结得出适合设计实用的一般规律。     

On the characteristics and design of yielding elements used in steel‐braced framed structures

In this paper, the behavior of a concentric braced frame structure equipped with yielding elements (YE), based on energy concepts, has been investigated extensively. When a severe earthquake occurs, energy will get absorbed through structural elements, which causes destruction. In order to reduce structural damage, input energy should be dissipated. YE will act as a fuse and absorb a great deal of earthquake input energy. Two one‐story steel frames with different bay‐to‐height ratios (B/H < 1 and B/H > 1) are investigated. YE is located in the braces intersection. First, through studying the elastic behavior of the frame, the best location, angle and shape of YE is proposed. Subsequently, a nonlinear dynamic analysis has been implemented to obtain the frames' response in different ground motions. In addition, the ratio of ‘dissipated energy by yielding elements’ to ‘total entering energy of structure’ is further calculated. Finally, an approximate method is presented for estimating the nonlinear behavior of the braced frame equipped with YE. This approximation transfers a complex problem into a set of practical graphs and charts. The comparison of the results between suggested method and time history analysis indicates very reasonable agreement between the two techniques. Copyright © 2010 John Wiley & Sons, Ltd.     

新型抗震体系隅撑支撑框架结构研究

新型抗震隅撑支撑框架(knee-braced frame,KBF)是在梁柱连接的附近设一起耗能作用的隅撑,主支撑连接在此隅撑上构成的抗震结构体系。与偏心支撑体系EBF抗震结构体系对比,具有大震时框架结构不易损坏、维修方便的优点。采用有限元考察了不同的隅撑形式、不同高宽比下KBF结构的性能。在分析总结的基础上,系统地提出了KBF框架的抗震设计要求和有关的计算公式。     

斜隅支撑体系的弹塑性性能分析

提出了一种新型耗能支撑框架钢结构体系——斜隅支撑框架体系,指出该体系具有延性好、抗侧移刚度大、震后容易修复的特点,分析了隅撑与梁柱的连接方式以及隅撑的布置方式对钢框架受力性能的影响。     

Parametric study and design approach of off‐center bracing systems

This paper presents an effective approach for the seismic design of off‐center bracing systems (OBSs). The nonlinear behavior of an OBS can be specified by evaluation of two yielding stages representing tensile yielding of different bracings. This can be achieved when stiffness of the corner brace member is deliberately considered less enough to act as a fuse‐like component. An accurate two‐dimensional finite element modeling for the geometric and material nonlinearity of such systems considering buckling behavior of the brace members is developed. Through an extensive parametric study, the optimal ratios of the influential parameters of OBS are obtained, and their effects on the nonlinear performance of OBS are evaluated. Next, a number of design graphs for determining the trilinear behavior model of different types of the OBS are presented. The aforementioned diagrams are included of non‐dimensional force and stiffness parameters that can be used for other frames with the same properties. Then, by extracting an equivalent bilinear model from the trilinear approximated behavior, an effective design algorithm based on the calculation of system's ductility under desired earthquake is presented, and finally, applicability of the proposed design approach is well demonstrated through an example problem.     

On the Evaluation of the Use of EKBs to Improve Seismic Performance of Steel Frames

In this paper a new eccentric and knee bracing system named Eccentrically Knee Brace (EKB) is introduced and its merits to increase seismic performance of the steel frames is investigated. To assess the seismic behavior of this system compared to other steel braced systems, numerical modeling using finite element software is implemented. Subjected to moderate earthquakes, the knee element exclusively dissipates the seismic energy through plastic shear distortion, while the other structural elements remain in elastic range. Under severe earthquakes, plastic deformation of the knee element will be halted by the stopper subsequently causing yielding of the link element. Finally, a simplified analytical model is derived to predict the bilinear behavior of the EKBs.     

蒙皮支撑的钢构件静力工作性能研究

提出了蒙皮支撑钢构件静力工作性能的非线性有限元分析方法，用该方法分析了蒙皮支撑梁和蒙皮支撑柱的基本受力性能，并考虑了多种因素对蒙皮支撑构件性能的影响。分析结果表明，蒙皮对构件的侧向支撑及扭转约束作用可以大大改善构件的静力性能并提高构件的承载力。     

钢结构交错桁架体系在强震作用下的破坏模式

对钢结构交错桁架体系在强震作用下的工作性能进行了研究。通过采用改进的静力弹塑性(NSP)分析方法,在对一个交错桁架体系实例的原结构方案进行修改的基础上,分析了交错桁架结构布置方案在强震作用下的破坏模式和延性要求的一般特性,得到了不同布置方案在强震作用下的破坏模式特点和各个楼层的延性要求。分析结果表明:在强震作用下交错桁架体系的塑性铰发展多集中在桁架腹杆中,柱中一般无塑性铰出现,结构刚度退化小,变形能力强,具有良好的抗震性能和延性能力。     

双塔高层建筑-多层地下室-桩-土系统动力相互作用研究

采用样条子域法、半解析无限元法和直梁的弯剪单元模型相耦合的方法 ,对带有多层地下室的桩承单、双塔高层建筑与周围土体组成的体系 ,在地震作用下的动力相互作用问题进行了分析研究。算例表明 ,本文方法具有输入数据简单、计算量较小、精度较高的优点 ,并且较好地反映了工程上此类建筑物考虑与地基共同工作时的动力性能和内在机理     

竖向承重与水平抗侧相分离的组合结构体系在地震作用下的受力机理分析

为提升装配式建筑的抗震性能、提高其标准化程度,提出了竖向承重与水平抗侧相分离的组合结构体系(以下简称"可分体系"),以某六层办公楼工程为实例设计了可分体系的结构方案,并对其在地震作用下的受力机理与传统刚接组合框架结构体系(以下简称"传统体系")进行了对比研究.利用有限元软件Midas Gen进行反应谱法设计,在此基础上...     

Effect of mid-connection detail on the behavior of x-bracing systems

In this paper, the effect of mid-connection detail of x-bracings comprised of build-up sections on the elastic-plastic behavior of braced systems is investigated. Then, a proposed symmetric mid-connection detail is compared with the commonly used one, analytically. In common mid-connection detail for build-up sections, one diagonal member (which is comprised of a pair of channels or angles) is usually discontinuous at the mid-connection and the other continuously passes through the connection. A rectangular gusset plate is used to join the discontinuous and continuous diagonals in practice. In the proposed method, one section from each diagonal member is discontinuous and the other is continuous. Buckling and post-buckling behavior of single span and single story models of cross-braced systems have been verified during a nonlinear static finite element analysis. The results show that the proposed mid-connection detail can improve both strength and ductility of cross-braced systems. Also, it is shown that adding two cover plates on both sides of discontinuous diagonal members in common mid-connection detail can partially improve the overall behavior of the system.     

Shaking table test of a steel frame with replaceable curved knee braces

为实现钢框架结构的震后快速修复，提出了一种配置可更换弧形角撑和高强钢构件的抗弯钢框架结构。在目标水准地震作用下，结构塑性变形集中在弧形角撑上，高强钢构件基本保持弹性以降低震后残余变形，震后可通过更换弧形角撑快速修复结构。为研究所提出结构体系的抗震性能以及更换弧形角撑的可操作性，设计了1个带混凝土楼板的1/2缩尺模型进行振动台试验。试验结果表明：该模型实现了预定的损伤控制机制，能够满足GB 50011—2010《建筑抗震设计规范》的最大层间位移角限值要求；由于该模型在超罕遇水准的地震作用下可以保持较大的屈服后刚度，因此其残余层间位移角很小(不超过0.028%)，震后弧形角撑易更换；更换弧形角撑后，模型得到了一定程度的修复，但混凝土楼板开裂使得模型刚度未能完全恢复;在重复强震作用下，模型的最大层间位移角未发生显著变化，弧形角撑耗能稳定，但部分弧形角撑的最大变形有所增大，损伤在模型各局部呈现出不均匀发展的趋势。     

配置可更换弧形角撑的钢框架结构振动台试验研究

为实现钢框架结构的震后快速修复,提出了一种配置可更换弧形角撑和高强钢构件的抗弯钢框架结构。在目标水准地震作用下,结构塑性变形集中在弧形角撑上,高强钢构件基本保持弹性以降低震后残余变形,震后可通过更换弧形角撑快速修复结构。为研究所提出结构体系的抗震性能以及更换弧形角撑的可操作性,设计了1个带混凝土楼板的1/2缩尺模型进行振动台试验。试验结果表明：该模型实现了预定的损伤控制机制,能够满足GB 50011—2010《建筑抗震设计规范》的最大层间位移角限值要求;由于该模型在超罕遇水准的地震作用下可以保持较大的屈服后刚度,因此其残余层间位移角很小(不超过0.028%),震后弧形角撑易更换;更换弧形角撑后,模型得到了一定程度的修复,但混凝土楼板开裂使得模型刚度未能完全恢复;在重复强震作用下,模型的最大层间位移角未发生显著变化,弧形角撑耗能稳定,但部分弧形角撑的最大变形有所增大,损伤在模型各局部呈现出不均匀发展的趋势。     

Performance‐based plastic design method for tall hybrid coupled walls

The research presented herein involves a performance‐based design method for a tall hybrid coupled wall (HCW) system. For this study, HCW structures were designed with a performance‐based plastic design (PBPD) method. This approach directly accounts for inelastic structural behavior and considers design lateral force distribution at ultimate limit state. The design concept uses a pre‐selected target drift and yield mechanism as key performance limit states. The yield mechanism consists of shear yielding in the coupling beams and flexural yielding of reinforced concrete walls at the bases. HCW structures with varying heights and coupling ratios (CRs) were designed and subjected to a series of nonlinear dynamic analyses. The results indicated that the CR strongly influences the response of the structure. The structures could also be under‐designed when the inelastic distribution of lateral forces owing to higher modes was not properly considered. Finally, a design method to account for higher mode effects within the PBPD framework was presented. The method was validated using the results from nonlinear analyses. Copyright © 2016 John Wiley & Sons, Ltd.     

跨层巨型斜支撑体系的节点分析与设计

对成都成达大厦跨层巨型斜支撑体系节点的受力特性进行研究。利用整体分析的结果,对典型节点进行壳体有限元建模,对节点区域的应力分布进行有限元分析。通过分析提出节点设计的若干措施。有限元分析表明,所采取的措施可行、有效。     

Performance assessment of innovative seismic resilient steel knee braced frame

Buckling restrained knee braced truss moment frame (BRKBTMF) is a novel and innovative steel structural system that utilizes the advantages of long-span trusses and dedicated structural fuses for seismic applications. Steel trusses are very economical and effective in spanning large distance. However, conventional steel trusses are typically not suitable for seismic application, due to its lack of ductility and poor energy dissipation capacity. BRKBTMF utilizes buckling restrained braces (BRBs) as the designated structural fuses to dissipate the sudden surge of earthquake energy. This allows the BRKBTMF to economically and efficiently create large span structural systems for seismic applications. In this paper, a prototype BRKBTMF office building located in Berkeley, California, USA, was designed using performance-based plastic design procedure. The seismic performance of the prototype building was assessed using the state-of-the-art finite element software, OpenSees. Detailed BRB hysteresis and advanced element removal technique was implemented. The modeling approach allows the simulation for the force-deformation response of the BRB and the force redistribution within the system after the BRBs fracture. The developed finite element model was analyzed using incremental dynamic analysis approach to quantify the seismic performance of BRKBTMF. The results show BRKBTMF has excellent seismic performance with well controlled structural responses and resistance against collapse. In addition, life cycle repair cost of BRKBTMF was assessed using the next-generation performance-based earthquake engineering framework. The results confirm that BRKBTMF can effectively control the structural and non-structural component damages and minimize the repair costs of the structure under different ranges of earthquake shaking intensities. This studies conclude that BRKBTMF is a viable and effective seismic force resisting system.     

Experimentally and analytically study on eccentrically braced frame with vertical shear links

The excellent hysteretic behavior of eccentrically braced frames (EBFs) using shear links have made these systems an effective alternative for both moment resisting frame as well as concentrically braced structures. Generally, horizontal shear links are located either at the middle or at the ends of the beam. However, large deformation of the shear links in those beam must be accepted under severe earthquakes. In those instance in which the beam have to remain elastic, vertical shear links should be designed underneath the beam thereby transferring the region of plastic deformation to location where they are tolerable and post‐earthquake repair or replacement of damaged parts is easier. In this paper, seismic behavior of vertical‐EBF (V‐EBF) have been considered experimentally and analytically. The required relation to design of the system have been proposed. In addition, to predict nonlinear behavior of V‐EBF systems, an analytical model including kinematic–isotropic strain hardening for shear, only kinematic strain hardening for moment, has been presented. Results showed a good convergence of the presented analytical model (with an upper bound for yielding surface to the V‐EBF) with experimental results.