Gusset Plate Connections Research Articles

Numerical and experimental investigations on inelastic cyclic performance of mid‐span gusset plate connections

SummaryThe design and detailing of gusset plate connections greatly influence the seismic performance of a special concentrically braced frame (SCBF). Recently, a balanced design approach has been proposed in order to develop significant inelastic deformation from multiple yield mechanisms and to delay the failure of connections of SCBF system. Although extensive studies have been conducted on the corner gusset plate connections of SCBFs, research on the detailing of mid‐span beam gusset plates is rather limited. This study aims at investigating the required free length for the detailing of the mid‐span gusset plates with different brace slenderness ratios. A nonlinear finite element analysis has been conducted for a braced frame with 4 different values of linear clearance in the mid‐span gusset plates and 2 values of brace slenderness ratios. In all simulation models, the corner gusset plates have been designed using balanced design approach and detailed using an elliptical clearance of 8 times the gusset plate thickness. An experimental study has also been conducted on 2 gusset plate sub‐assemblages having similar brace slenderness ratio but with 2 different values of linear clearance in the middle gusset plates. The lateral drift capacity corresponding to the brace fracture and the level of damage are found to be dependent on the detailing of the gusset plates. Based on the results of numerical and experimental studies, the required free length has been recommended for the detailing of middle gusset plates of SCBFs of different brace slenderness ratios.

Evaluation of the Effect of End-Connection Specifications on Lateral Bearing Capacity of Concentrically Braced Steel Frames

Concentrically braced steel frames should be capable of bearing considerable amounts of lateral force. The connection of these frames to beams and columns plays an important role in this respect. This connection is designed to either prevent end-connection problems caused by free buckling of a member or reinforce the gusset plate to reduce damages caused by possible buckling of a member at the connection. In order to assess seismic and buckling behaviors of braces under different conditions, 8 single-span one-story frames with diagonal braces were studied using a finite-element software. The first two models were implemented to assess the impact of end clearance, while the other six models were used to study the effects of different stiffeners on the gusset plates. Results showed that, proper incorporation of stiffeners can prevent early failure of the gusset plate connection and enhance post-buckling behavior.

Cyclic Performance of Braces with Different Support Connections in Special Concentrically Braced Frames

Gusset plate connections between the steel braces and the supporting frame members play an important role in the performance of special concentrically braced frames (SCBFs) under earthquake loading conditions. Extensive studies have been conducted on SCBFs in which the gusset plate connections are designed to ensure the out-of-plane buckling of steel braces. However, research on the cyclic behavior of gusset plate connections allowing the in-plane buckling of braces is very limited. An experimental investigation has been carried out in this study to investigate the cyclic performance of the in-plane buckling of gusset-brace assemblies. Tests showed that the gusset plate connections detailed for in-plane buckling of braces provided performance at par with those detailed for the out-of-plane deformation arrangement. A numerical comparative study on three types of connection arrangements has also been conducted, namely, a) out-of-plane buckling of braces using gusset plates, b) in-plane buckling of braces using knife plates, and c) direct connection of braces without using any gusset plates. Braces made of hollow steel sections having constant slenderness ratio and width-to-thickness ratio are used in all the numerical models. The main parameters compared are the energy dissipation capacity, displacement ductility, patterns of failure, and the sequence of yielding in the components. Both test and analysis results are used to quantify the performances of gusset plate connections in order to achieve an efficient and reliable concentrically braced frame systems.

Seismic Design of Gusset Plate Connections in Concentrically Braced Frames

In concentrically braced frames (CBF), gusset plates as the connected members are subjected to forces not only from brace but also from frame action. When the braced frame is deformed, the beam-column connection will deform, and the deformation of beam-column connection either “open” or “close” as the brace under “compression” or “tension”. Therefore, the design of gusset plate should consider the effect of such frame action, in addition of the brace axial load. Six finite element models were developed using ABAQUS to investigate the force distribution of gusset plate under the two actions. It is noted that force in gusset plate can be divided into two parts and frame action is so small that can be neglected during brace buckling.

On-Line Testing of Steel Brace Connections Using Non-Linear Substructuring and Force-Displacement Combined Control

The present paper suggests an on-line hybrid test environment for evaluating the seismic performance of steel bracing connections. The test method combines substructuring techniques and finite element analysis. The behavior of the brace member is simulated by the finite element analysis program ABAQUS, while the bracing end connections are physically tested. Two actuators are used to simulate the physical continuity between the analytical and experimental substructures by controlling axial load and out-of-plane rotation. A MATLAB user subroutine is created as the interface between the main control program and ABAQUS to impose the target rotation and axial force to the connection quasi-statically. A gusset plate connection designed to behave as a pin connection is tested and its efficiency to accommodate inelastic rotations up to a 4.0% story drift is evaluated. The test method is reasonable and smooth operation is achieved. The test system ensures pragmatic loading and boundary conditions to the brace connections, which are tested in full interaction with the brace member until failure. The maximum strength and rotation capacity of the connection can be clarified under actual cyclic inelastic rotations and varying axial loads derived from the inelastic behavior of the brace member.

Study on Strength and Stiffness of Meranti Wood Truss with Plywood Gusset Plate Connection and Lag Screw Fastener

Wooden truss could be one of the options to be used as structural element both in building or bridge. Wooden truss overcomes the limitation of timber with great dimension with necessary strength. In this study, the wooden truss was designed with Meranti wood type with elasticity modulus of 10,520 MPa and specific gravity of 0.8. The timber used has cross-section size of 45 mm × 45 mm, with truss frame span of 2,445mm and height of 400 mm. The connection between the timbers was using 18 mm thick plywood with 6 mm lag screw fastener. The destructive testing that was conducted on 3 test samples showed a result that the strength of the truss was at an ultimate load of 31,042 N with a ductility ratio of 5.61. Numerical study of the truss’ stiffness with this connection model resulted in stiffness degree value of 0.94.

A component method for cold-formed steel beam-to-column bolted gusset plate joints

Cold-formed steel elements are being used more frequently on construction sites because of the good strength-to-cost ratio. Researches on such structures show that, in most cases, the behaviour of the constitutive joints is semi-rigid. However, insufficient studies are published examining the properties of these joints. This paper presents a study of cold-formed steel bolted gusset plate connections based on the component method approach. The component method considers any joint as a set of individual basic components. In this procedure, the joints are analysed using mechanical models that are able to simulate moment – rotation M – φ relationship. In this paper the joint is analysed as made of three springs: beam bolt group, column bolt group and gusset plate. A “three springs” mechanical model and a technique to calculate joint stiffness is presented. The results predicted through the proposed mechanical model are validated through comparisons to experimental and finite element results.

Shake Table Testing of Concentrically Braced Steel Structures With Realistic Connection Details Subjected to Earthquakes

This paper describes an experimental investigation into the seismic response of concentrically braced steel frames (CBFs). Twelve shake table tests were performed on full-scale single storey frames, each containing a pair of identical brace members. The experimental programme examined the behaviour of brace members with four different square and rectangular hollow cross-sections and a range of gusset plate connection details. The aim of the experimental study was to determine the influence of brace and gusset plate properties on CBF response from serviceability to ultimate limit states, including collapse. Consequently, all test frames were subjected to three levels of seismic excitation: (i) low-level excitation to examine elastic frame response, (ii) medium-level excitation to examine brace buckling and yielding effects, and (iii) high-level excitation to induce brace fracture. A detailed set of data on the seismic response of CBFs with realistic brace members and connections were obtained from the tests. The experiments were conducted under representative dynamic response conditions as opposed to the conventional idealised quasi-static loading procedures employed in previous experimental investigations of CBF behaviour. The results faithfully capture the behaviour of brace-gusset plate test specimens with different non-dimensional brace slenderness, brace cross-section slenderness, connection types and gusset plate detailing. The response variables measured in each test included the shaking table and frame accelerations and displacements, brace elongation and axial force, and brace member and gusset plate strains. The experimental observations include elastic frame vibration properties, acceleration and drift demands, ultimate failure modes and ductility capacity. The brace-gusset plate test specimens remained elastic at low-level excitations, brace buckling and yielding occurred in all medium-level excitation tests, while specimens exhibited brace fracture under high-level excitation. Fracture did not occur in the gusset plate connections irrespective of whether these were designed using a conventional design method with a Standard Linear Clearance (SLC), or a balanced design with an Elliptical Clearance (EC). However, the balanced design approach showed more uniform distribution of plastic strains and led to higher brace ductility capacities when compared to the conventional design method. Based on the test results, available methods for predicting the ductility of bracing members are compared and assessed, and a number of considerations for design are highlighted and discussed.

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.

On‐line hybrid test method for evaluating the performance of structural details to failure

SummaryA test environment to evaluate the seismic performance of gusset plate connections intended for steel braced frames is proposed. The developed test method combines the substructuring techniques with finite element analysis methods in an on‐line hybrid scheme. Numerical substructure analysis is conducted on bracing members, while bracing connections are treated as experimental substructures. A force‐displacement combined control imposed with the aid of 2 jacks ensures physical continuity between the analysis and test. The rotational behavior of gusset plate connections subjected to large inelasticity and varying axial loading until fracture is investigated. Two gusset plate details were designed and tested to verify the efficiency of the proposed method. The test method is rational, and smooth operation is achieved. The test results revealed the advantage of the developed on‐line hybrid test method in exploring the ultimate capacity of bracing connections.

03.03: Feasibility of hybrid simulation for testing steel connections of braces with intentional eccentricity

ABSTRACTAn online hybrid test environment to examine the seismic performance of the gusset plate connections of steel braces is developed by incorporating sub‐structuring techniques and finite element methods. In the developed test system, the behaviour of the brace member is simulated by the finite element analysis program ABAQUS, while the brace end connection is physically tested. Two hydraulic jacks are used to simulate the physical continuity between the analytical and experimental substructures by controlling axial load and out‐of‐plane rotation. A MATLAB user subroutine is created as the interface between the main control program and ABAQUS to impose the target rotation and axial force to the connection quasi‐statically. A gusset plate connection designed to behave as a pin connection is tested and its efficiency to accommodate inelastic rotations was evaluated up to 4% story drift. The test method is reasonable, with smooth operation and ensures realistic loading and boundary conditions.

11.57: Assessment of the ductile behaviour of CBF structures considering energy dissipation in bolted joints

ABSTRACTIn dissipative seismic concept according to Eurocode 8, capacity design leads to additional cost for brace connections. In this concept, connections, either bolted or welded, remain elastic during seismic events whereas the braces dissipate energy by yielding and buckling. However the bolted gusset plate connections of braces are able to dissipate energy by sliding, bearing and block shear when minimal requirements are fulfilled. Within the RFCS project Meakado, both experimental tests and numerical simulations have been performed on bolted connections under cyclic actions to assess this potential dissipative mechanisms. An equivalent non‐linear spring model has been calibrated from these results to represent the ductile behaviour of concentrically braced frames (CBF) bolted joints when the non‐ductile mechanisms are prevented. Taking into account this equivalent spring model, the seismic global behaviour of CBF structures in the context of moderate seismicity have been studied both by time history and by push‐over analyses. Finally this paper proposes a calibration of the behaviour factor q of CBF structures when energy dissipation is considered in the bolted connections of braces together with the braces dissipation. The scope of application of these results is discussed.

01.15: Numerical investigation of preloaded gusset plate connections between polygonal built‐up members

ABSTRACTIn the last decades, the demand for renewable energies, including wind energy, is increasing. With this increase, more powerful wind energy converters are needed, which require higher supporting structure that allow to reach zones of higher wind speed with less turbulences. The most commonly used type of the tower is steel tubular tower. Height of these towers is limited by manufacturing and transportation logistics. The solution to overcome these issues might be construction of lattice towers. The major disadvantage of lattice towers is large number of the installed bolts. Therefore, the steel hybrid tower that combines the advantages of steel lattice (lower part) and tubular tower (upper part) was proposed in SHOWTIME project. The sections used in lattice portion of the tower are built‐up polygonal sections composed of cold‐formed pieces connected together with preloaded bolts. The goal with using built‐up polygonal cross‐section is to minimize number of connections by increasing the member length. The focus in this paper is numerical investigation of preloaded gusset plate connections between these types of members. The finite element software ABAQUS has been used in the study. The aim of the investigation is to determine the failure modes of the elements and connections, as well as stiffness and ultimate resistance of the connections.

01.21: Static and cyclic behaviour of bolted gusset plate connections: Numerical and analytical modelling

ABSTRACTIn dissipative seismic concept according to Eurocode 8, capacity design leads to additional cost for brace connections. In this concept, connections, either bolted or welded, don't dissipate energy, this role being dedicated to braces. However bolted gusset plate connections of brace are able to dissipate energy by sliding, bearing and block shear. Within the RFCS project Meakado, the seismic behaviour of these shear joints and their influence on the global resistance of the concentrically braced frame (CBF) have been studied performing time history analysis on CBF structures where springs were introduced at the location of connections. To calibrate this spring model, tests on bolted connections of single channel and double angles have been performed by Tecnalia during this project and completed by a numerical simulations based on the finite element code ANSYS. The results of the numerical simulations are presented in this paper. The model is firstly confronted to experimental tests and a parametrical study has been carried out to extend the domain of validity and particularly to study connections of tubes. Finally, an equivalent spring model, based on the component method of Eurocode 3, supposed to represent the behaviour of connections in seismic nonlinear analyses is developed.

Shake table assessment of gusset plate connection behaviour in concentrically braced frames

Diagonal bracing members and their connections to beams and columns are the key lateral resisting components in concentrically braced frames (CBFs). Although gusset plate connections are widely used to connect bracing and frame members in such systems, their design often involves significant simplifications and idealisations due to the complexity of their behaviour under seismic loading. A conventional approach, which utilises a standard linear clearance zone that permits out-of-plane brace deformation, is typically used in the design of gusset plates. This approach can result in overly large connections with cumbersome details. The desire to achieve an improved balance between the gusset over-strength, on the one hand, and a favourable overall frame performance coupled with practical connection detailing, on the other, has prompted proposals for an improved design approach. However, before new recommendations on the design of gusset plate connections can be provided for use in codified guidance, there is a need to assess the performance of such detailing alternatives under realistic earthquake loading conditions. Accordingly, in this study, the performance of different brace connection configurations and gusset plate designs are examined using shake table testing. The paper describes twelve single-storey full scale shake table tests, which were performed on the AZALEE seismic testing facility at CEA Saclay. In seven of these tests, the gusset plates at the end of the brace members were connected to both beam and column flanges, while in the other five tests these were connected to the beam flange only. Conventional gusset plate design with a standard linear clearance was used for six tests, whereas a more balanced design with a nonlinear elliptical clearance detail was used for the others. The experimental set-up, specimen details, and loading procedures are presented, together with a detailed account of the results and observations. The main findings and their implication on the performance at the local component, as well as the overall frame levels, are highlighted. In particular, it is shown that, provided a number of recommendations are followed, the balanced design approach using a nonlinear clearance can enhance the overall drift capacity, while maintaining control of the failure mode within the bracing member.

Recommendations for numerical modelling of concentrically braced steel frames with gusset plate connections subjected to earthquake ground motion

Concentrically Braced Steel Frames (CBFs) are commonly used as an economic and effective means of resisting the lateral loading induced during earthquakes and limiting the associated displacements. Here, an integrated experimental and numerical approach is taken to investigate the performance of CBFs subjected to seismic action of varying intensity. As part of the BRACED transnational research project, shake table experiments on full-scale single-storey CBFs recorded the response of test frames employing various combinations of bracing member sizes and gusset plate connection details to simulated ground motions scaled to produce elastic response, brace buckling/yielding and ultimately brace fracture. This recorded experimental data is used to validate a numerical model developed using the OpenSees seismic response analysis software. Key experimental and numerical model responses are compared. The sensitivity of the model to variations in modelling parameters is assessed and recommendations for future numerical modelling are presented. Results indicate model performance is sensitive to the initial camber applied to the brace members, with a value of 0.8% of overall brace length observed to achieve a more accurate representation of global frame stiffness and drift response than the lower values previously recommended in literature, but an underestimate of the compression resistance of the brace.

Crack propagation modelling for high strength steel welded structural details

Nowadays the barrier of applying HSS (High Strength Steel) material in bridge structures is their low fatigue strength related to yield strength. This paper focuses on the fatigue behaviour of a structural details (a gusset plate connection) made from NSS and HSS material, which is frequently used in bridges in Hungary. An experimental research program is carried out at the Budapest University of Technology and Economics to investigate the fatigue lifetime of this structural detail type through the same test specimens made from S235 and S420 steel grades. The main aim of the experimental research program is to study the differences in the crack propagation and the fatigue lifetime between normal and high strength steel structures. Based on the observed fatigue crack pattern the main direction and velocity of the crack propagation is determined. In parallel to the tests finite element model (FEM) are also developed, which model can handle the crack propagation. Using the measured strain data in the tests and the calculated values from the FE model, the approximation of the material parameters of the Paris law are calculated step-by-step, and their calculated values are evaluated. The same material properties are determined for NSS and also for HSS specimens as well, and the differences are discussed. In the current paper, the results of the experiments, the calculation method of the material parameters and the calculated values are introduced.

BEHAVIOUR OF A GUSSET PLATE CONNECTION UNDER COMPRESSION

The paper presents behaviour of gusset plate connections in compression. The finite element method is employed to examine the buckling resistance of the gusset plate connections. The FE model is validated to results of physical tests and verified by an analytical solution based on existing formulas. Finally, a parametric study is performed. The studied parameters include gusset plate thickness and size, types of connection between the gusset plate and frame members and stiffeners.

On the tensile capacity of single-bolted connections between GFRP angles and gusset plates-testing and modelling

The polymer composite known as Glass Fibre Reinforced Polymer (GFRP) has several advantages over conventional materials. It has been slowly incorporated into civil infrastructures. Because of lack of knowledge about the behaviour and design criteria of structural connections, the wide-spread application of GFRP in this field has been rather limited. In this study, analytical and experimental behaviour of GFRP structural angle members with gusset plate connections for net-tension strength, with an emphasis on transmission line tower connections, were investigated. Thirty-five single-lap, single-bolted connections were tested. The widths of the gusset plate and edge distance were varied. A tensile load was applied on the joint and then failure modes and the corresponding loads were observed. The effect of the plate width and edge distance on the connection efficiency was also studied. Based on the studies, the optimum plate width and edge distance were determined as three and five times diameter of the bolt, respectively. A semi-empirical analytical stress concentration model proposed by Hart-Smith (1978), is adopted to determine the cross-correlation coefficient 'C' which is linearly correlated to the stress concentration factors of composite and elastic isotropic materials. Using regression analysis, the coefficient 'C' was obtained, and an ultimate net-tension strength design formula is proposed.

Secondary frame action in concentrically braced frames designed for moderate seismicity: a full scale experimental study

European seismic design codes do not take into account the strength and stiffness of the secondary frame action provided by bracing gusset plates of concentrically braced frames (CBFs). This is an attractive assumption for practicing engineers, as it provides simplifications during the analysis and design phases. However, when efficiency and economy are concerned, especially in low-to-moderate seismic regions, this normally neglected frame resource may be interesting to consider in design. Gusset plates can provide a certain degree of stiffness and strength following the bracing failure, and may even prevent global collapse. In particular, when the shear deformation demand of the braced cell remains limited, as in the case of low-to-moderate seismic actions, it may become reasonable to take this extra stiffness and strength into account. Ongoing research project RFSR-CT-2013-00022 MEAKADO investigated this phenomenon by means of experimental and numerical studies with the perspective of setting new inputs for the design rules of the future generation of Eurocodes. This paper presents the results of full scale tests performed inside this research project, which characterized resistance, stiffness, and ductility resources of CBF systems designed for moderate seismicity. The paper also quantifies the effective contribution of the frame action, provided by gusset plate connections, to the global performance of CBF frames.