Effect of mid-connection detail on the behavior of x-bracing systems (2025)

Stability analysis and design of double shear lap bolted connections in steel x-bracing systems

Elsevier, 2019

In this paper elastic and inelastic buckling analysis of the bolted double shear lap connections (DSL) are investigated , which are commonly used in concentrically braced steel frames comprised of cold-formed hollow structural section (HSS), as brace members. By the lack of any approach to evaluate the compression strength of a DSL connections, their design is usually relied on the tension load demand developed in the brace member. The results of quasi-static cyclic tests performed on six full-scaledX-bracing specimens have shown that the discontinuous brace member with DSL connection, not designed for compression, failed and fractured by the buckling at the connection. In all the specimens, the typical brace buckling only occurred in the continuous members , as expected. In this study. a simplified elastic stability analysis is employed to calculate elastic buckling load and effective length factor usable for the design of DSL connections. Anon-linear static analysis is also performed on a suggested numerical model comprised of beam-column elements to predict the response of the studied X-bracings, exhibiting the connection and member buckling. It is shown that the results of the both suggested design procedure based on the stability analysis and the numerical model agree well with the buckling load of the test specimens. It is also indicated that the slip of connection plates decreases the compression capacity and should be considered in the analysis and design procedures.

Validation of a CHS connection used in X-bracing diagonals

The present paper investigates the behaviour of a connection widely used at the co-planar intersection of circular hollow sections (CHS), a case very common in X-bracings. The performance of this type of connection is validated by means of finite element modelling. Our connection is made up of two separate gusset plates, welded externally along the generatrices of the cylindrical surface of a CHS (in an ear-like manner), so as to accommodate the terminal gusset plates of the interrupted CHS: in this way the two bars intersect and remain on the same plane.

Effective Length Factor for Discontinuous X-Bracing Systems

Journal of Engineering Mechanics, 2001

In this paper the elastic stability analysis of X-bracing systems is performed. Special attention is focused on the effect of midspan (center) connection on the out-of-plane buckling load of these systems. Commonly, in practice, one of the diagonal members is discontinuous at the midspan intersection and a gusset plate is used to connect the members. So the center connection is modeled as partly pinned or semirigid. In this study the closed-form relationships are obtained for the evaluation of effective length factor of X-bracing with pinned end connections and either pinned or semirigid (discontinuous) midconnection. The tension and compression diagonals are assumed to have different section properties and axial loading. The results are graphically displayed for some practical cases. Three types of double angles X-bracing with different detailing for midconnection are compared. The numerical results show that the discontinuous center connection can affect the buckling load and effective length factor of diagonal members and it should be considered in the design of X-bracing systems.

Effects of Local Eccentricity of Connecting Braces on Nonlinear Behavior of Steel Concentric Brace Connections

According to most current building codes, in order to prevent a steel brace from brittle behavior due to buckling, it is necessary to use prescribed stronger and stiffer sections. However, experience from past earthquakes has shown that the above requirement is not effective in containing the brittle failure of members, not even in postponing this unwanted behavior. It is well known that one of the factors affecting dynamic behavior of a brace is its end condition, i.e., the stiffness of connection plates known as gusset plates (GP). In this paper through numerical simulation it is suggested to offset the connecting members at the connection to enhance the ductility and even strength of the connection itself. For the purpose of this research work, numerical models are studied using nonlinear static analysis. A very good match is shown to exist between results of computer simulation and experimental results, making it possible to study much more models at less time, effort, and cost,...

Analytical Investigation of the Effect of Steel X-Bracing Connection Type to the Reinforced Concrete Frames

2021

Using steel braces is regarded as one of the significant methods for retrofitting and seismic rehabilitating of reinforced concrete frames. Thanks to its easy implementation, economic considerations and appropriate seismic retrofitting performance against lateral forces, this system has received more attention from researchers in comparison with other seismic resistant systems. In this type of structural system, the connection properties are of high significance which can play a significant role in the obtained results including ductility, resistance, stiffness, etc. The detailed behaviour and performance of this type of connection have received less attention from researchers; hence, it is regarded as an under-researched issue which we have addressed in the present study; we made an effort to explore and investigate this issue comprehensively. ABAQUS finite element software was applied for modelling and numerical analysis; a total of 8 models were analysed and investigated which we...

Behavior and analysis of bracing connections for steel frames

Journal of Constructional Steel Research, 1994

This paper presents the second part of the results of a study devoted to the analysis of heavy steel bracing connections, and to the effects of those connections on the behavior of braced frames subjected to static loads. The paper deals initially with the finite element analysis of one type of bracing connection, in which the structural fasteners such as bolted clip angles and fillet welds are modeled using the two-dimensional nodal interface element developed in a previous companion paper. Next, two series of full-scale tests of bracing connections subjected to tensile loading are described and the responses measured during the tests compared with the predictions. Good agreement was found between tests and predictions when the overall performance of the bracing connection is not strongly influenced by slip in the bolted fasteners. Lastly, one series of tests on beam-to-column connections made up of friction-bolted double clip angles is presented to validate the finite element model for this type of connection. Once validated, the finite element analysis is used to derive fundamental bracing connection flexibilities and the relative strength interaction domain to be used in a companion paper.

Buckling-restrained braced frame connection performance

Journal of Constructional Steel Research, 2010

Large-scale experimental studies of buckling-restrained braced frames (BRBFs) have shown that although they display good overall seismic performance, they may have limitations due to connection failure modes that do not allow the braces to realize their full ductility capacity. These experimental results motivate further investigation of BRBF connection behavior. In this study, nonlinear finite element models are used to study BRBF beam-column-brace connections. The models focus on a one-story subassembly extracted from a previously-tested, four-story BRBF. After the baseline finite element analysis results are verified with experimental data, parametric studies varying the connection configuration are used to assess the key factors influencing performance. Connection configuration is shown to have a significant impact on global system response and localized connection demands.

Investigation of RBS Connection Ductility in Eccentrically Braced Frame

Procedia Engineering, 2011

In the eccentrically braced frames (EBF) in which one end of the link is connected to a column, the integrity of the link-to-column connection is essential to the ductile performance and safety of the EBF. But among of all tests that have taken place on this connection, because of the intensity of stresses on the link to column connections, the tested specimens were confronted with brittle and sudden failures. So it seems that the reduced beam sections (RBS), in flexural yielding links can be a suitable solution for raising this problem by concentrating stresses at a location away from the connection. Therefore in this paper, by using a finite element program ETABS and with nonlinear static analysis (pushover), the possibility of keeping the plastic hinge away from the location of link-to-column connection by using the RBS connection, were researched in a dual system of special moment frame and special eccentrically braced frame. According to this research, the models with RBS, by earlier developing the hinge at the RBS region, can delay yielding occurrence of link at the column face (at least prior to achieving the moment at the location of maximum flange decrease of RBS region) to 1.1 times its expected plastic moment capacity.

Seismic response of braced frame connections

2004

Seismic response of braced frames largely depends on the response of braces. In high seismic zones in the United States, two systems are currently being used; special concentrically braced frames (SCBF) and concentrically braced frames with buckling restrained braces (BRCBF). Braces in SCBF systems develop their inelastic action through compressive buckling and tension yielding. Buckling restrained braces (BRB) are encased in an unbonded, stiff material that restricts brace buckling and they develop their ductility through compression and tension yielding. In both types of systems gusset plate connections are used to connect the brace to the framing elements. These different systems place different demands on the connection by the brace depends on the brace type. Braces in SCBF systems place large axial and out-ofplane rotational demands on the brace as a result of brace buckling. The stiffness of BRB can result in large in-plane moment and axial force demands. The connection design must account for these different demands.

Analysis of flexibly connected braced steel frames

Journal of Constructional Steel Research, 1994

This paper presents the third part of the results of a study devoted to the analysis of heavy steel bracing connection, alut to the effects of those connections on the behavior of braced frames subjected to static loads. The paper presents initially a model compatible with standard frame analysis computer programs and capable of capturino the basic behavior of bracing connections. This is accomplished by representing the bracing connection by an equivalent three-member truss whose behavior can simulate relevant stiffness and strength of the prototype connection. This equivalent truss model is applied to the analysis of a single-story braced frame under service loads, and the sensitivity of the frame to different bracing connection stiffnesses, beam~to-column connection rotational rigidities and brace eccentricities is explored. Lastly, a more complex eight-story braced structure is analyzed under factored loads by yielding of connections and members to demonstrate the inelastic capabilities of the approach.