Numerical simulation of gusset plate connections with rectangular hollow section shape brace under quasi-static cyclic loading

In concentrically braced frames, gusset plate connections to rectangular hollow section braces are fabricated using welds to connect the gusset plate to both brace and flanges of the beam and of the column framing into the brace. The beam-to-column connection at the gusset plate is either welded or bolted. However, past experimental studies have indicated that undesirable failure modes could occur in the gusset plate even when using a linear clearance rule in the design of the gusset plate, especially when connecting hollow rectangular shapes.For these reasons, this study investigates through numerical analyses the local seismic performance of gusset plate connections with fully restrained beam-to-column connections as well as partially-restrained bolted connections. The latter are provided at the outside corner of the gusset plate, away from the face of the column, in order to facilitate the beam rotation at the bolted connection upon continued lateral deformation. The main goal of the study of the local performance of gusset plate connections is to validate the design procedure presented in this paper; to compare the various clearance rules proposed in the literature and to propose an alternative clearance rule to the linear clearance rule.The local performance is examined through detailed finite element models of a braced bay located at the ground floor of a four storey concentrically braced frame using the MIDAS finite element program. Finally, local performance of the models is compared in terms of strain concentrations in gusset plates, beams and columns.     

Cyclic behavior of concentrically braced frames with built-up braces composed of channel sections

Concentrically braced frames are earthquake resistant systems commonly used in buildings. Seismic behavior of this type of structures is affected by their configurations, brace properties, and brace to gusset plate connections. In this paper, the results of three experiments conducted to investigate the cyclic behavior of concentrically braced frames with braces built-up of double channels are reported. Significant damage was observed in beam to column connections. Large out of plane deformation of braces caused some cracks in the connector welds; however they did not result in fracture. Although large drift was applied to the frames, no brace fracture was observed. Furthermore, experiments showed that the majority of compressive strength in post-buckling state and a noticeable portion of tensile strength originated from frame action. By choosing connector spacing as the main parameter and using finite element models, a parametric study was performed to investigate the effect of this parameter on this type of frames with two different details of brace to gusset plate connections. It is observed that reducing the connector spacing increases the inelastic strain demand in braces and decreases it in gusset plates. However, gusset plates, which accommodate 2t linear clearance, are less dependent on connector spacing, compared to those accommodating 6t elliptical clearance. It seems that the limitations of slenderness ratio of individual section, stipulated in current seismic provisions, need further study.     

Lateral cyclic behavior of zipper braced frames-considering connection details

During Northridge earthquake in USA in 1994, a variety of failures occurred in welded steel connections. Studying these structural failures has led to development of more reliable moment resisting connections and new ways of using braced frames as seismic load resisting systems. This article investigates through numerical simulations, the lateral capacity and seismic behavior of two of these newly-thought braced frames, zipper braced frames and suspended zipper braced frames. The overall seismic behavior of these frames is investigated through displacement-based pushover analyses considering the effect of connection elements such as gusset plate and shear tab. To study the efficiency of these two types of concentrically braced frames, a numerical investigation on their behaviors for low-, mid- and high-rise buildings was conducted. Three zipper braced frames and three suspended zipper braced frames with different number of stories have been modeled using OpenSEES software. For each simulation, frame maximum strength, maximum drift capacity, and weight are determined and compared with each other. It is concluded that connection modeling has significant effects on the lateral behavior of these frames. Furthermore, the suspended zipper braced frames show higher ductility when compared with the ductility of zipper braced frames. Finally, the suspended zipper braced frames are recommended to be used in high-rise buildings, however, for the lowand mid-rise buildings it is recommended to use zipper frames due to economic efficacy.     

Simulated behavior of multi-story X-braced frames

Steel braced frames are a commonly used seismic resisting system and thus, multi-story X-braced frames are frequently used. However, research into the behavior of these systems with midspan gusset plates, as used in practice, is limited. As a result, their seismic performance and the influence of connection design on this performance are not well understood. A comprehensive series of inelastic analyses were undertaken to better understand the nonlinear, cyclic behavior of multi-story X-braced frames and their gusset plate connections. Finite element (FE) analyses were conducted and the FE model was developed and verified by comparing the simulated results with cyclic tests and nonlinear analyses of single story systems, conducted at the University of Washington. The verified analytical model and associated failure estimation procedures were used to predict all yield mechanisms and failure modes, frame deformation capacity, and initial cracking and fracture of critical elements within the frame. A parametric study was performed to examine the influence of the gusset plate, framing members and other structural elements on the seismic performance of multi-story X-braced frames. The results show that the design and detailing of the gusset plate has a significant impact on the seismic performance of the frame. Connections designed with proposed end-rotational clearance models, and with strength and stiffness values balanced to the buckling and tensile yield capacities of the brace provided the best ductility and deformation capacity. In addition, the results suggest that floor slabs, gusset plate stiffeners and framing member sizes affect the frame performance and must be considered in the analysis and design of the system.     

基于滑移连接的防屈曲支撑钢框架节点抗震性能研究

防屈曲支撑（BRB）是一种拉压均可全截面屈服耗能而不屈曲的金属阻尼器,在建筑结构的抗震减震设计中得到广泛应用。然而,由于大变形下支撑框架节点存在显著开合效应,在罕遇地震作用下易出现节点板和相邻梁柱构件的提早断裂现象,限制了BRB抗震性能的充分发挥。为此,在总结BRB钢框架节点的现行设计方法及节点失效模式基础上,提出了可释放节点开合效应的滑移连接节点板,采用低摩擦材料减小接触面摩擦力。建立有限元模型,通过与传统焊接节点板对比,分析两种不同连接对节点板、梁柱和BRB受力性能的影响。以此为基础,设计该类节点足尺试验模型,对其进行拟静力试验,分析其在往复荷载下的抗震性能。研究结果表明：所提出的滑移连接可有效释放节点板与梁柱之间的切向约束和开合效应,显著降低了节点板的塑性损伤,实现了罕遇地震作用下节点板弹性的性能目标;梁塑性铰由节点板端部移至梁柱交界面处,降低了梁柱构件的剪力水平和塑性损伤;在层间位移角4%下各关键构件仍具有饱满稳定的滞回性能,显著提高了BRB钢框架的抗震性能。     

低屈服点钢扣板连接的试验研究

同心支撑框架被广泛用于钢结构房屋的抗震设计中。在地震激励下,同心支撑框架的支撑会承受循环拉压荷载。由于支撑的屈曲,其抗压强度通常低于抗拉强度,这可能会降低支撑框架的抗震性能。该文对采用弱扣板强支撑的设计理念进行了验证。扣板选用低屈服点钢(LYP),从而使设计的扣板在支撑屈曲前发生屈服。低屈服点钢的屈服强度很低,但其延性很好。通过一系列试验验证循环荷载作用下低屈服点钢扣板的性能。研究发现,在低屈服点钢扣板上增加槽型约束(STR)可以大大提高其抗震性能。在拉压荷载作用下,有槽型约束的低屈服点钢扣板可以提供类似大小的强度。扣板的耗能能力同样得到提高。基于此研究成果,给出低屈服点钢扣板的一些设计建议。     

Experimental study of low yield point steel gusset plate connections

Concentrically braced frames have been used widely in the seismic-resistant design of steel building structures. During earthquake excitation, the braces of the concentrically braced frame are subjected to recursive tensile and compressive forces. The compressive strength of the brace is usually less than its tensile strength because of the buckling of the brace, and this may degenerate the seismic resistance capacity of the braced frame. In this reported research, an alternative design concept that adopts the weak gusset plate-strong brace is examined. The gusset plate is designed to yield prior to the buckling of the brace. Low yield point (LYP) steel is selected for the gusset plate. The LYP steel possesses low yield strength and high elongation capacity. A series of experimental studies was carried out to examine the LYP steel gusset plates under cyclic loads. It is found that adding slot-type restrainers (STR) to the LYP steel gusset plate greatly enhances the seismic resistance of the gusset plate. The proposed LYP steel gusset plate with an STR is able to provide similar strengths under tensile and compressive loads. The energy dissipation capacity of the gusset plate is also increased substantially. Based on this study, suggestions are made for the design of LYP gusset plates.     

工字截面倒V型支撑及其节点板在循环荷载作用下的性能研究

倒V型支撑及其中心节点板连接在特殊中心支撑框架中备受青睐。为了提高其抗震性能和在抗震设计中的应用,对9个非弹性往复荷载作用下的工字截面倒V型支撑及其节点板的滞回性能进行试验和数值模拟。主要参数为:节点板上支撑端部间隙、支撑杆件节点位置、自由端长度与节点板厚的比值。在支撑低周疲劳破坏前,框架的极限承载力并没有降低,但有一个长期的低承载稳定阶段。虽然有直线间隙的试件抗震性能良好,但只要节点板不先于支撑破坏,也可以不设间隙。中等偏心的支撑节点性能很好且尺寸也很经济,但节点板上的支撑杆件位置可能引起板面外变形并降低结构延性。基于试验结果,提出节点板自由边长度与厚度比值限值。     

防屈曲支撑角部节点板与钢框架的相互作用效应

防屈曲支撑是一种高效稳定的耗能减震装置,其与框架结构一般通过焊接节点板形式连接。目前节点板连接设计方法仅考虑支撑轴力的影响,并没有直接考虑框架开合效应(梁柱在水平地震力下产生的张开/闭合变形)的不利作用,导致焊接节点板在连接处提前发生开裂。通过有限元模拟的方法,同时考虑开合效应和支撑轴力的共同影响,对防屈曲支撑钢框架与角部节点板连接的相互作用进行研究。有限元模型共5组,主要参数包括节点板尺寸、节点板与框架的连接形式以及节点板是否设置自由边加劲肋。在连接形式方面,提出了一种可减小开合效应不利影响的新型可滑移螺栓连接节点板,并与传统焊接节点板的受力性能进行比较。分析结果表明,平面尺寸较小的焊接节点板对结构的抗侧刚度影响最小,可减小设置防屈曲支撑的子框架所分担的地震剪力,相应的节点板受力性能也优于平面尺寸较大的焊接节点板|在焊接节点板上设置自由边加劲肋并不能明显改善其受力性能|所提出的新型可滑移螺栓连接节点板可有效减小节点板对结构刚度的影响,以及框架开合效应对节点板的不利影响,是一种在消能钢框架支撑体系中具有应用前景的新型节点板连接。     

翼缘削弱型节点空间钢框架在低周反复荷载

为研究翼缘削弱型节点空间钢框架在低周反复荷载作用下的抗震性能,采用有限元分析软件ABAQUS对普通节点和翼缘削弱型节点的空间钢框架模型进行有限元模拟,对2种钢框架模型的破坏形式、承载力、滞回性能、耗能能力、强度及刚度退化性能等进行了对比分析。结果表明:翼缘削弱型节点可使梁端塑性铰外移至梁端翼缘削弱处,避免梁端焊缝处应力集中导致脆性破坏;翼缘削弱型节点等效粘滞阻尼系数与普通节点空间钢框架相比有明显的提高,进入屈服阶段后由于应力重分布,其刚度及承载力退化速度较普通节点空间钢框架慢,翼缘削弱型节点钢框架具有梁铰延性破坏机制,抗震性能较好。     

Influence of connection design parameters on the seismic performance of braced frames

Special concentrically braced frames (SCBFs) are commonly used lateral-load resisting systems in seismic design. In SCBFs, the braces are connected to the beams and columns by gusset plate connections, and inelastic deformation is developed through tensile yielding and inelastic post-buckling deformation of the brace. Recent experimental research has indicated that the seismic performance of SCBFs can be improved by designing the SCBF gusset plate connections with direct consideration of the seismic deformation demands and by permitting yielding in the gusset plate at select performance levels.Experimental research provides important information needed to improve SCBF behavior, but the high cost of experiments limits this benefit. To extend and better understand the experimental work, a companion analytical study was conducted. In an earlier paper, the inelastic finite element model and analysis procedure were developed and verified through detailed comparison to experimental results. In this paper, the model and analytical procedure extend the experimental results. A parametric study was conducted to examine the influence of the gusset plate and framing elements on the seismic performance of SCBFs and to calibrate and develop improved design models. The impact of the frame details, including the beam-to-column connections, the brace angles, and their inelastic deformation demands, was also explored. The results suggest that proper detailing of the connections can result in a large improvement in the frame performance.     

Compressive behavior of central gusset plate connections for a buckling-restrained braced frame

Buckling-restrained braced frames (BRBFs) are used as lateral-load resisting systems in seismic design. The braces in BRBFs are connected to beams and columns by gusset plate connections, and can yield in both tension and compression instead of buckling. Although tests of buckling-restrained braces (BRBs) have demonstrated their ability to withstand significant inelastic axial deformation, large-scale BRBF tests have exhibited central gusset plate buckling before BRBs develop the ultimate compressive strength. To extend and better understand the experimental work, this paper presents an analytical study of the compressive behavior for BRBF central gusset plate connections using the finite element computer program ABAQUS. A model of a previously tested BRBF is conducted to predict experimental buckling load of the central gusset plate and verify the accuracy of a simple model of a central gusset plate connection including a beam and part of the BRB. The out-of-plane deformation of the central gusset plate resembles the buckled shape of a gusset plate with low bending rigidity provided by the BRB end. The experimental buckling load of the central gusset plate cannot be predicted based on the AISC-LRFD approach with an effective column length factor of 1.2. Therefore, a parametric study on the compressive strength of BRBF central gusset plate connections is conducted with various gusset plate dimensions and free-edge stiffeners. An inelastic plate buckling equation together with coefficient charts is proposed to predict ultimate load. For gusset plates with sufficient free-edge stiffener rigidity, the yield load can be developed and increased to the post-yield strength level. A required free-edge stiffener size is also recommended for BRBF central gusset plates to develop compressive yield load.     

无支撑半刚性连接钢框架的简化分析

用变刚度的螺旋弹簧模拟梁柱节点半刚性连接的弯曲特性 ,建立了半刚性连接钢框架梁单元的刚度矩阵。通过分别引入横梁修正线刚度和修正转动刚度 ,将等效代替框架法和无剪力分配法推广应用于无支撑半刚性连接钢框架的结构分析 ,其计算十分简便     

Cyclic behavior studies on I-section inverted V-braces and their gusset plate connections

Inverted V-braces and their central gusset plate connections are popular patterns of brace arrangements for special concentrically braced frames (SCBF). To improve the understanding of their seismic performances and promote their applications in seismic designs, the hysteretic behavior of nine I-section inverted V-braces and their gusset plate connections subject to inelastic cyclic loading is examined through experiments and analytical simulations. It is found that the clearance at the brace end on the gusset plate, the locations of the intersection point of bracing members, and the ratio of the free edge length to the gusset plate thickness are the key parameters. The loading capacities of braced frames show no decrease before the brace low-cycle fatigue fracture, but a longer plateau at a lower load level exists in the hysteretic loops. Although specimens with a linear clearance exhibit better seismic behaviors, a negative clearance is also acceptable as long as the gusset plate does not fracture prior to the braces. A brace intersection point with moderate eccentricity is preferable for its better behavior and its economical dimension of the gusset plate, but the brace point location in the gusset plate could induce out-of-plane deformations in the gusset plate and cause the system ductility to deteriorate. Based upon test results, a suggested limitation of the ratio of the free edge length to thickness for the gusset plates is presented.     

高层装配式斜支撑钢框架结构设计研究

针对远大S30工程的高层装配式斜支撑钢框架结构体系,分别采用振型分解反应谱法和线性时程分析法对整体结构进行有限元分析,得到了结构在多遇地震作用下的内力和位移响应。进行了结构整体的弹性设计,总结了该结构体系的设计方法。按规范对柱与柱座法兰连接的承载力进行了计算,并通过有限元分析和试验研究进行了节点强度和刚度的分析与验证。对梁柱节点进行了试验,研究其刚度变化规律,提出了采用弹簧单元在整体结构中建立节点简化分析模型的方法。研究结果表明：该体系中轻型钢楼梯对整体刚度的影响可以忽略,计算时可不建模分析;结构抗震性能满足现行规范要求,结构侧向变形曲线介于框架结构和剪力墙结构变形曲线之间;斜支撑降低了节点区的应力,增大了结构体系刚度,起到了减小柱计算长度、增强梁柱节点和柱与柱座连接的作用;柱与柱座法兰连接设计既满足设计强度要求,又实现了柱的刚性连接,保证了柱承载力和刚度的连续性。     

不同刚度比下防屈曲支撑钢筋混凝土框架抗震性能试验研究

为研究不同刚度比防屈曲支撑(buckling-restrained brace,BRB)钢筋混凝土框架的抗震性能,设计并制作了3榀BRB水平刚度与主体框架抗侧刚度比值分别为3、5、7的减震框架,通过低周往复荷载试验,对比研究其耗能减震能力、破坏形态、BRB连接节点及节点板性能、BRB转动变形性能、BRB端部附加弯矩产生机制等,探讨与BRB连接的梁、柱构件设计方法。研究结果表明：3榀框架滞回曲线饱满,耗能能力稳定,随着刚度比的增加,屈服荷载及极限荷载提高,BRB连接节点破坏越严重;BRB连接节点板的存在使框架柱塑性铰位置由柱端移至节点板趾部附近区域;水平荷载作用下,各框架中BRB端部由于转动变形产生附加弯矩,转动变形与层间位移角近似呈线性变化关系;加强消能子结构的延性构造措施是实现大变形下BRB充分耗能的有效途径。     

大直径钢管混凝土柱-H形钢梁节点设计研究

在传统内环板节点的基础上,提出一种适用于大直径钢管混凝土柱的梁柱节点。为了避免内环板宽度过大造成混凝土浇筑困难、用钢量较大的问题,在内环板焊接拉结钢筋,既可以减小钢材用量又便于在钢管柱内设置钢筋笼。为避免与钢梁翼缘焊接处的钢管表面发生层状撕裂,局部加大梁端翼缘宽度,并通过分析合理确定梁端扩翼宽度与扩翼角度。采用非线性有限元软件,对节点构造与应力分布、变形性能的关系进行分析。通过对比分析得到梁端的刚域长度,并对刚域长度与框架梁抗弯刚度的关系进行研究。为了验证该类节点设计的合理性,进行钢管混凝土柱-H形钢梁缩尺模型试验。有限元分析与缩尺模型试验结果表明,节点拉结钢筋可以提高内环板传力的有效性,有效减小节点区柱壁应力,当梁端扩翼宽度为1.5倍梁翼缘宽度、扩翼角度为1∶6时,节点区柱壁应力明显低于H形钢梁的应力,满足“强节点弱构件”的抗震设计理念。节点刚度对钢管混凝土柱-H形钢梁框架结构的侧向刚度影响显著,当梁端刚域长度约为钢柱直径的0.4倍时,框架梁的抗弯刚度可增加40%以上。节点抗震性能良好,可以实现“强节点弱构件”的抗震设计理念。     

Compressive behavior of dual-gusset-plate connections for buckling-restrained braced frames

This work conducts compression tests and finite element analyses for steel dual-gusset-plate connections used for buckling-restrained braced frames (BRBFs). Compared to a single-gusset-plate connection, dual gusset plates sandwiching a BRB core reduce gusset plate size, eliminate the need for splice plates, and enhance connection stability under compression. The experimental program investigated ultimate compression load by testing ten large dual-gusset-plate connections. Out-of-plane deformation of the gusset plate in the test resembled that of a buckled gusset plate with low bending rigidity provided by the BRB end. The general-purpose nonlinear finite element analysis program ABAQUS was applied for correlation analysis. A parametric study of the dual-gusset-plate connection was performed to study the effects of plate size, presence of centerline stiffeners, and beam and column boundaries on ultimate compression load. The ultimate compression load of the dual-gusset-plate connection could not be predicted based on the AISC-LRFD approach due to beam flange out-of-plane deformation. The ultimate compression load of the dual-gusset-plate connection was reasonably predicted using a column strip length from the Whitmore section to the workpoint of the beam and column centerlines and a buckling coefficient of K = 2.     

中柱失效下预制装配式框架结构抗连续倒塌性能研究

为了研究中柱失效下预制装配式框架结构的抗连续倒塌性能,制作了5个两跨1/3缩尺梁-柱子结构模型,采用pushdown加载方式研究其在倒塌过程中的抗力机制与破坏模式。试验结果表明：采用顶底角钢连接、无黏结预应力拼接以及混合连接等三种连接方式对其抗连续倒塌性能及抗力机制影响很大;由于纵筋在梁柱节点区域不连续,无黏结预应力连接结构不能发展有效的弯曲机制,而在梁柱界面上安装顶底角钢时,则可以发展较好的弯曲机制;预制装配式结构的破坏模式和抗力机制与普通混凝土结构明显不同,预制装配式结构抗力从加载初期就主要由预应力钢筋发展悬链线作用提供。通过高精度有限元软件LS-DYNA进行精细化有限元建模,在验证数值模型的基础上开展参数分析。有限元分析结果表明：装配式结构中采用有黏结预应力筋可以增大结构在小变形阶段的承载能力,而在大变形阶段,有黏结预应力筋断裂更早,变形能力更弱,承载力也较低。     

盐雾环境下锈损钢框架梁柱节点抗震性能试验研究

为研究盐雾环境下锈损钢框架梁柱节点抗震性能的退化规律,对7个不同锈蚀龄期焊接梁柱节点试件开展三维形貌扫描和拟静力试验,研究了锈蚀损伤对框架梁柱节点滞回行为、破坏形态、承载性能、转动变形和耗能能力的影响.研究结果表明:锈蚀梁柱节点滞回环形状虽然较为饱满,但是其包络面积、加卸载刚度和循环圈数明显减小;锈蚀梁柱节点破坏模式均...