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.     

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.     

负偏心对钢管插板K型节点承载力的影响

对主管规格为φ 219 mm×6 mm有负偏心作用的1/4加肋钢管插板连接的极限承载力进行了试验研究,根据试验结果提出了等效受力模型,在此基础上研究了有负偏心的1/4(1/2)和全环形加强板钢管插板连接的K型节点的主管轴力、主管管壁弯矩和剪力三者之间的相互关系,并利用有限元软件分析了各参数对节点极限承载力的影响,在此基础上提出了此类节点的建议公式并与试验结果进行了比较.结果表明:建议公式表面看是反映两两之间的相互关系,实际上是反映了主管轴力、主管管壁弯矩和剪力三者之间的关系,建议公式能较好的估算节点承载力的上限值.     

Ultimate strength of gusset plate connections with fillet welds

Braced frames are commonly used as lateral-load resisting systems in seismic design. The braces are connected to the beams and columns by gusset plate connections. Fillet welds are commonly used to connect the gusset plates to the beams and columns. And the fracture of the interface welds were observed in the past research and earthquakes. This paper focused on the ultimate strength of interface weld connection between gusset plate and frame elements when the brace is in tension. Pilot experimental study was conducted with four specimens and proved that the evaluation recommended by AIJ works well. A verified finite element analysis model was developed to conduct a parametric study. The studied parameters are the brace angle, gusset plate size, and eccentricity of brace. From the parameter study, it is confirmed that the tensile brace axial force is primarily transferred to the interface weld within an extension Whitmore region, which is named as the effective region in the AIJ evaluation. And the extension Whitmore region is affected by the gusset plate geometrical constraint. A revised extension Whitmore region is suggested by considering the aforementioned parameters. The AIJ evaluation using the revised extension Whitmore region is also compared with the UFM, and showed better evaluation for the rectangular shape gusset plate.     

输电塔钢管-插板连接节点板承载力研究

输电工程中输电塔架节点通常采用节点板连接的方式,其受力情况非常复杂。通过对5组输电塔架典型节点的足尺试验和有限元分析,考察节点板的受力性能和破坏模式,并利用多参数有限元分析不同破坏模式下宽厚比、无支长度以及节点板构造等主要参数对节点板承载力的影响,提出有(无)加强环板的节点板承载力计算方法,并与试验和有限元所得的结果进行比较。结果表明:基于插板连接的节点板建议计算方法合理有效,具有较好的适用性。     

Nonlinear finite element analysis of CFT-to-bracing connections subjected to axial compressive forces

The Abaqus finite element program together with nonlinear material constitutive models for concrete-filled tube (CFT) and steel gusset plate is used to analyze the behaviors of the gusset plate type CFT-to-Bracing connections subjected to axial compressive forces. It is found that the failure of CFT-to-Bracing connections occurs below the connecting area. Local bulged shapes of the steel tube might take place in the areas close to the gusset plate and the fixed end under the failure stage. The ultimate strengths of the CFT columns slightly increase with the increasing of the load ratio and the thickness of the gusset plate. The introduction of the cutouts on the gusset plates slightly increases the ultimate strength of the CFT column and causes more local bulged shapes on the steel tubes below the connection area under the failure stage.     

空间板节点的非线性分析与极限受压承载力研究

本文提出一种改良的网架节点型式一空间板节点。现行规范中板节点的计算方法多是依据强度条件得出的,而当节点板在轴压作用下,可能在达到屈服强度以前就发生整体失稳,因此有必要对板节点的受力性能进行深入分析,提出相应节点的计算方法。本文采用有限元软件ABAQUS建立板节点数值模拟模型,通过变参数分析考察了节点板厚度和无支长度等因素对节点板受压性能的影响,并将结果与现行规范计算值进行对比分析,提出了单面连接节点板极限受压承载力的计算方法,并对其适用性进行了验证。     

广西体育场空间相贯节点试验研究

为考察构造复杂的广西体育馆多支管相贯节点的受力性能和极限承载力,对4个试件的1：2．5缩尺模型进行试验,同时对K形插板加劲节点进行有限元分析。试验结果表明,试件的承载力都能达到设计荷载水平的2倍以上,且节点区无宏观破坏现象。试验结果和有限元分析结果证明,节点区管件加厚和设置插板等加强措施是有效的。     

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.     

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.     

单角钢连接节点板受压性能试验研究与承载力计算方法

输电工程中输电塔架节点通常采用节点板连接的方式,单角钢杆件受轴向压力作用时,节点板处于偏心受力状态,常规的节点板受压承载力计算方法都是基于双角钢连接轴心受压得到的,与输电塔架节点板的受力存在明显差别。通过对2个输电塔架典型节点进行足尺试验和有限元分析,考察了单角钢连接节点板的受压性能和破坏模式,并利用多参数有限元分析结果,研究了用于单角钢连接节点板受压承载力的计算方法。试验研究表明,单角钢连接节点板受压时出现明显的板面外失稳,且节点板的变形呈现出弯曲伴随扭转的形式。通过对比分析表明,有限元分析结果与试验结果吻合较好。基于柱模型和板模型提出了单角钢连接节点板受压承载力的计算方法,分析表明,两种模型都能较好地预估单角钢连接节点板的受压承载力。     

钢管混凝土桁架新型节点试验研究

对6个圆形钢管节点板式节点和6个钢管混凝土节点板式节点进行了对比试验研究。试验结果表明:空钢管试件在达到极限荷载时,节点板下空钢管发生严重局部屈曲而丧失承载力;钢管混凝土节点则在节点板下只发生轻微局部屈曲现象,具有较高的承载力。相比之下,钢管混凝土的承载力明显高于空钢管的承载力,并具有更好的延性性能。在钢管混凝土桁架中采用节点板式节点可比相贯节点更加方便、可靠。     

X形圆管斜插板节点轴压性能试验研究

对10个X形圆管斜插板节点试件在插板轴压力作用下的承载性能进行单调加载试验研究。以插板厚度和插板平面与圆管轴线平面之间夹角为变化参数进行节点轴压性能试验,研究了X形圆管斜插板节点在插板轴压力作用下的破坏模式,分析了荷载-端板位移曲线,节点区域应变强度分布,以及插板相对厚度（插板与圆管厚度比值）、插板平面与管轴线之间夹角对节点轴向承载力和延性的影响。试验结果表明：当插板相对厚度较小时（取值为0.89）,夹角基本不影响圆管斜插板节点的承载力;插板相对厚度较大时（取值为1.33）,随着夹角增大圆管斜插板节点的轴压承载力呈逐渐增大的趋势;随着插板相对厚度的增大,轴压承载力增大;薄插板（插板厚度为4 mm）节点试件的大多数测点保持弹性;而厚插板（插板厚度为6 mm）节点试件的大多数测点进入塑性状态;插板相对比较薄的情况下,IIW规范的计算值偏于不安全;插板相对较厚时,IIW规范计算结果偏于安全。     

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.     

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。     

Cyclic flexural analysis and behavior of beam-column connections with gusset plates

This research investigates the cyclic flexural behavior of double-angle concentrically braced frame beam-column connections using three-dimensional nonlinear finite element analysis. Prior experimental research demonstrated that such connections possess appreciable flexural stiffness, strength, and ductility. The reserve capacity provided by these connections plays a significant role in the seismic behavior of low-ductility concentrically braced frames, so knowledge about the impact of connection parameters on local limit states and global connection performance is needed for employing reserve capacity to design and assess concentrically braced frames. Finite element models were developed and validated against prior experiments with focus on the limit states of failure of the fillet weld between the gusset plate and beam, low-cycle fatigue fracture of the steel angles joining the beam and gusset plate to the column, and bolt fracture. The models were used to evaluate the flexural stiffness, strength, and ductility of braced frame connections with primary attention on the effects of beam depth, angle thickness, and a supplemental seat angle. The finite element analysis demonstrated that increasing beam depth and angle thickness and adding a supplemental seat angle all increased the stiffness and strength of the connection while maintaining deformation capacity. A procedure to estimate the flexural behavior of beam-column connections with gusset plates was developed based on the results of the numerical simulations.     

Comprehending the ductile behavior of slotted bolted connections

Structural steel special moment frames are designed to resist earthquakes with substantial inelastic energy dissipation. The ductile beam‐to‐column connections become more popular over these years by dissipating the earthquake input energy at beam ends. The paper provides a comprehensive study of a high‐strength slotted bolted connection (SBC). Slotted holes instead of round holes are used for the connection such that frictional sliding could be developed. Experimentally, a standard bolt–weld connection as well as three similar slotted bolted connections were designed and tested. The load‐carrying capacities, the ductile deformations, the energy dissipation capacities, and the hysteretic characteristics of the specimens were presented. The overall performance of the steel connections by replacing the circular holes with slotted holes is evaluated, and the design recommendations of the flange gusset plate with slotted holes are provided. Numerically, the nonlinear SBC behavior was simulated and calibrated against the experimental results. The SBC effectiveness as well as the parametrical influences have been presented in details. Results show that the friction slippage behaviors of the specimens with slotted holes provide better ductility, higher plastic deformation capacity, and increased load‐resisting capacities near the ultimate strength.     

T形钢管混凝土插板连接节点受弯性能研究

采用精细化有限元分析方法对T形钢管混凝土插拔连接节点的平面内受弯性能进行了研究.首先通过与试验结果进行对比,验证了精细化有限元模型的正确性和准确性.在此基础上研究了主管壁厚、支管壁厚、主管形式和混凝土强度对节点破坏模式和承载力的影响.结果表明,钢管混凝土插板连接节点的破坏模式和钢管插板连接节点不同,为主管冲剪破坏和支管...     

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.     

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。