T-stub Connections Research Articles

Steel and Composite Structures

The component-based method is widely used to analyze the initial stiffness of joint in steel structures. In this study, an analytical component model for determining the column face stiffness of square or rectangular hollow section (SHS/RHS) subjected to tension was established, focusing on endplate connections. Equations for calculating the stiffness of the SHS/RHS column face in bending were derived through regression analysis using numerical results obtained from a finite element model database. Because the presence of bolt holes decreased the bending stiffness of the column face, this effect was calculated using a novel plate-spring-based model through numerical analysis. The developed component model was first applied to predict the bending stiffness of the SHS column face determined through tests. Furthermore, this model was incorporated into the component-based method with other effective components, e.g., bolts under tension, to determine the tensile stiffness of the T-stub connections, which connects the SHS column, and the initial rotational stiffness of the joints. A comparison between the model predictions, test data, and numerical results confirms that the proposed model shows satisfactory accuracy in evaluating the bending stiffness of SHS column faces.

Experimental and numerical study on the T-Stub behaviour with preloaded bolts under large deformations

The bolts and their arrangement strongly influence stiffness, strength and ductility of T-Stub connections. Preloaded bolts are typically adopted to improve the stiffness and limit the opening of the connection under serviceability conditions. EN1993-1-8 allows using two types of high resistance preloaded bolts, namely the German HV (acronym of Hochfeste Bolzen mit Vorspannung, which is the German for High Resistance bolts for pretension and the British/French HR (acronym of High Resistance) without making any distinction. However, the tensile failure modes of these bolts are different (i.e. nut stripping for HV and shank necking for HR) and may affect the ultimate tensile response of the T-Stub connections with weak bolts (e.g. failure mode type 2 and 3). Furthermore, despite the effects of geometrical non-linearities at large deformations are not specifically addressed in current codes, the membrane action developing in the flange and the shear force and bending moment in the bolt may influence the reserve of ductility of the T-Stub that plays an important role in case of seismic and robustness scenarios. In addition, the presence of initial imperfections (e.g. the misalignment of the web as respect to the bolts and the flange bowing) can influence the non-linear behaviour of the connection. The influence of all these aspects on resistance and ductility of T-Stub connections are investigated by means of both experimental monotonic tests and parametric finite element analyses. On the basis of the obtained results, design rules are discussed with the aim to guarantee extra ductility of T-Stub connections.

Experimental and numerical studies of bolted T-stub steel connection with different flange thicknesses connected to a rigid base

This paper presents experimental and Finite Element (FE) analyses of T-Stub steel connections. Such connection may be classified as rigid, semi-rigid, or flexible. For rigid T-Stub, no praying action is observed. For flexible T-Stubs, praying action may overload the bolts. A better knowledge of the contact stresses distribution between T-Stub flange and support base helps understand the resistance mechanism of the T-Stub connections. The contact area between T-Stub flange and support base depends largely on the flange thickness. This paper investigates the effect of the thickness of T-Stub connections fixed to a rigid support base. Nonlinear FE models utilizing ABAQUS software were developed to study the behavior of T-Stub connections. The results obtained from FE analyses were verified against experimental results. A parametric study was conducted to observe the effects of flange thickness on (a) the contact stress distribution between the flange and rigid base, (b) the prying actions on bolts, and (c) the shear stresses on bolts. The results from experimental tests and FE analyses were compared with T-Stub resistance capacity calculated using the provisions of Eurocode-3 and AISC.

Static Strength of Friction-Type High-Strength Bolted T-Stub Connections under Shear and Compression

The friction-type high-strength bolted (FHSB) T-stub connection has been widely used in steel structures, due to their good fatigue resistance and ease of installation. While the current studies on FHSB T-stub connections mainly focus on the structural behaviors under both shear and tensile force, no research has been reported on the mechanical responses of the connections under the combined effects of shear and compression. To make up for this gap, this paper presents a novel FHSB T-stub connection, which is simple in structure, definite in load condition, and easy to construct. Static load tests were carried out on 21 specimens under different shear–compression ratios, and the finite-element (FE) models were created for each specimen. The failure modes, initial friction loads and ultimate strengths of the specimens were compared in details. Then, 144 FE models were adopted to analyze the effects of the friction coefficient, shear–compression ratio, bolt diameter and clamping force on the initial friction load and ultimate strength. The results showed that the FHSB T-stub connection under shear and compression mainly suffers from bolt shearing failure. The load–displacement curve generally covers the elastic, yield, hardening and failure stage. If the shear–compression ratio is small and the friction coefficient is large, its curve only contains the elastic and failure stage. The friction coefficient and shear–compression ratio have great impacts on the initial friction load and ultimate strength. For every 1 mm increase in bolt diameter, the initial friction load increased by about 10%, while the ultimate strength increased by about 8.5%. For each 10% increase/decrease of the design clamping force, the initial friction load decreases/increases by 7.8%, while the ultimate load remains basically the same. The proposed formula of shear capacity and self-lock angles of FHSB T-stub connection can be applied to the design of CSS-enhanced prestressed concrete continuous box girder bridges (PSC-CBGBs) and diagonal bracing.

Study on New Bolted T-Stub Connection with Inserted Plates under Axial and Cyclic Loads

The bolted T-stub connection joining beam with column is being widely applied. To enhance the energy dissipation capacity of conventional T-stub connections, two rectangular plates are proposed to be inserted between the T-stub and column, so that the T-stub flange can yield both under tensile and compressive loads. This study put forward a mechanical model of a new T-stub connection with inserted plates and investigated important factors that could affect its mechanical behavior through experimental tests. Thirty specimens were designed with different configurations that differed according to the existence or absence of inserted plates, the fabrication method and the width of inserted plates. These configurations were tested under axial and cyclic loading conditions, and results showed that the proposal aiming to improve the energy dissipation capacity was feasible. The mechanical model presented coincided with the test observation and data. The advent of two inserted plates elevated the load bearing capacity, stiffness and ductility of connections under compression, whereas in tension the properties were not substantially enhanced. The welded T-stub connections outperformed those cut from standard section steel. The energy dissipated by connections with inserted plates was about 150% of that by traditional connections without inserted plates. Only within a reasonable range can the increment of plate width promote the energy dissipation capacity of T-stub connections. The optimum width of plates in terms of energy consumption accounted for around 31% of the overall width of connections.

Seismic performance analysis of steel beam to CFST column connection with ductility and energy dissipation components

Concrete-filled steel tubular (CFST) column to steel beam joint with the ductility and energy dissipation components is a type of connection which is used in prefabricated structures, to improve the capacity of connections and construction efficiency. In this paper, two different type of steel beam to CFST column connections with the penetrated high-strength bolts and end-plate are investigated, i.e., steel beam to CFST column connection with end plate (CJ-1), and T-stub bolted (CJ-2) connections. The finite element model (FEM) of steel beam to CFST column connection with the penetrated high-strength bolts under cyclic loading are conducted based on the whole process of the nonlinear explicit analysis method using ABAQUS. The feasibility of FEM is verified by a set of experimental results performed by our research group, as well as available test results from other researchers. The failure modes, bearing capacity, energy dissipation capacity and ductility and rigidity degeneration were studied. As a result, the load-displacement hysteretic loop curve of CJ-2 connection is plump. However, the hysteresis curve of CJ-1 shows pinching phenomenon. The value of buckling load and ultimate load of CJ-2 increased by 28 % and 30 % respectively, compared with CJ-1. With respect of stress analysis, the plastic strain accumulation position distribution is relatively uniform duo to the T-stub connection, avoiding the penetrated high-strength bolt early yield or fracture. The results show that the steel beam to CFST column connection with penetrated bolts and T-stub connection has good seismic capacity.

Investigations on prying forces in flexible connections of steel beams

PurposeThe use of flexible connections throughout the steel structures provides a high level of stiffness compared to that of fully welded connections. Flexible connections allow for rotation to an extent, which make them perform better during earthquake than welded connections. In hanger connections, the applied load produces tension in the bolts and bolts are designed for tensile forces. When the deformation of the flange plate is equal to that of the bolts, a plastic hinge is formed in the flange plate at the weld line and the bolts are pulled to failure. If the attached plate is allowed to deform, additional tensile forces called prying forces are developed in the bolts. The paper aims to discuss these issues.Design/methodology/approachThis paper includes the results of investigation on prying force in T-stub connection fabricated with normal grade bolts and high strength friction grip (HSFG) bolts. Finite element analysis has been carried out by creating models and analyzing the effect of external tensile force and bolt force. For different grades of bolt (4.6, 8.8, 10.9, 12.9), the prying force is calculated.FindingsIt is found that prying force is increasing with the change in grade of bolt used from normal to HSFG. The results obtained from analysis using IS 800:2007 codal provision are also included. It is observed that HSFG bolts do not allow for any slip between the elements connected and hence rigidity is increased.Originality/valueThe prying force mainly depends on geometrical parameter of the connection. In this research work, the variation of prying force was studied based on the variation in dimensions of T-stub angle section and bolt grade (4.6, 8.8, 10.9, 12.9). The method of obtaining prying force from bolt load and applied load is a unique approach. The results of FE analysis is validated with the analytical calculation as per IS 800:2007 code provisions, which shows the originality of the research.

Seismic behavior of semi-rigid steel joints—Major axis T-stub and minor axis end-plate

Due to its cost-effective nature and satisfactory seismic performance, semi-rigid steel frame is often considered as an alternative to conventional fully rigid steel frames. To date, the seismic behavior of semi-rigid connection has typically been documented in two dimensions. To fill this gap, an experimental investigation was made to study the behavior of the internal semi-rigid joints through spatial quasi-static tests with loads applied to the ends of the columns from both the major and minor axes. In our newly proposed semi-rigid joint, the minor beam is attached to the column web by an end-plate connection and the major one attached to the column flange by a T-stub connection, where the loading effect from the minor direction on the major direction of semi-rigid joints was considered. Results show the major beams failed with T-stub fractures and the minor beams failed with substantial bending deformations at the end-plates, which are easy failures to repair. In addition, the initial rotational stiffness and angular ductility coefficient of the minor beam decreased with increases in the thickness of the end-plate. Compared with the semi-rigid steel joints with T-stub connections in both axes, the major beams of our proposed joints exhibited obviously increased bending resistances, equivalent viscous damping coefficients and equivalent energy dissipations.

Seismic performance of beam to column connections with T-shaped slit dampers

In this paper, a new steel yielding damper in the beam-to-column connections relying on the combination of slit damper and T-stub called T-SSD is proposed, with an aim to increase energy dissipation capacity and stiffness as well as to reduce seismic damage on the structure. Different patterns of connections are considered in the analysis. Nonlinear finite element method is employed to deal with realistic modeling of the specimens and to capture all the main seismic behavioral aspects including the strength, the stiffness, the energy dissipation, ductility, von-Mises stress and equivalent plastic strain distributions of models. A parametric study on the geometry of slit dampers is also performed to determine the best geometrical configurations in terms of mechanical performance. According to the results, the models with T-SSD systems possess satisfactory hysteretic performances. Yielding and local buckling of the T-SSDs under seismic events serve as the primary source of energy dissipation, while the other structural components remain essentially elastic. Strength and energy dissipation capacities were essentially improved by changing the slits configuration. The T-SSD connections can supply the highest initial stiffness, bearing capacity, ductility, and energy dissipation increases by 63%, 94%, 80%, and 35%, respectively, with respect to the T-stub connection. The presence of shear tab in connections could typically result in increased initial stiffness by as much as 25% in comparison with counterpart without shear tab. Theoretical equations estimate the initial stiffness and bearing capacity of the connections 15% more than and 50% less than those of the numerical results, respectively.

Design finite element model of a bolted T-stub connection component

The paper is focused on a design approach to a T-stub component, which is key part in an analytical/numerical prediction of behaviour of the bolted end plate connections, by the Component Based Finite Element Method (CBFEM). The method combines the analytical Component Method and the numerical Finite Element Method (FEM). The distribution of internal forces is solved by the FEM. The connectors' behaviour is modelled by analytical models implemented into FEM as components. The method is developed for design of generally loaded complex joints with end plated where the distribution of internal forces is not clear. The resistance of the joint is controlled by limiting the plastic strain of plates and the strength of connectors, e.g. welds, bolts, and anchor bolts. The prediction of the initial stiffness and the deformation capacity is included natively. The T-stub in tension is investigated in this paper. CBFEM is verified on the research oriented model, which is validated against the authors' own experiments and the results from literature, and on the Component Method.

TESTS ON LOAD-CARRYING BEHAVIOR OF STAINLESS STEEL BOLTED T-STUB CONNECTIONS

A total of 14 stainless steel bolted T-stubs were tested under monotonic loading. The ultimate strength, failure modes and prying forces of the test specimens were obtained. The effects of the key parameters including the flange thickness, flange material grade, bolt diameter and bolt preloading were analyzed. It was revealed that the introduction of bolt preloading had little effect on the ultimate strength and failure mode, but resulted in increased initial stiffness for the T-stub specimens. The failure mode of the T-stub connections depended on both the tensile strength of the bolt and the flexural strength of the flange. The prying forces increased gradually with reduced flange thickness and bolt diameters, while the prying forces corresponding to the ultimate strength were not influenced by the bolt preloading. The test results were further compared with the strength predicted by the existing European, American and Chinese design codes. It was found that the existing design provisions were generally conservative for stainless steel bolted T-stub connections, among which the American code provided relatively better predictions. It may be attributed to the use of material tensile strength instead of yield strength.

Numerical Study on Ultimate Deformation and Resistance Capacity of Bolted T-Stub Connection

Disproportionate or progressive collapse is a phenomenon in which entire structure or large part of it collapses because of the local failure of a structure. Resistance to such progressive collapse depends on continuity between elements and ductility of the connections. The ductility of commonly used bolted end plate connections may depend on the T-stub component of the connection. The aim of this paper is to study the behaviour of T-stub components of beam to column end plate bolted connections under large deformation demands associated with column loss scenario. For this purpose, a parametric study is carried out to evaluate the ultimate strength and deformation capacity considering two parameters i.e. distance between the bolts and endplate thickness. Based on the experimental data, numerical model has been validated and employed in a parametric numerical study aimed at improving the response under large deformation demands. The study indicate significant role of bolts in development of catenary forces since the ultimate tensile capacity of T-stub after undergoing large deformation in a ductile failure mode was controlled by the failure of the bolts. Parametric study reveals much higher bolt force in comparison with displacement controlled induced axial force in the T-stub indicating failure of the bolts at much lower applied axial force.

Energy based design of a novel timber-steel building

Energy-based methodology is utilized to design novel timber-steel hybrid core wall system. The timber-steel core wall system consists of cross laminated timber (CLT), steel columns, angled brackets and t-stub connections. The CLT wall panels are stiff and strong, and ductility is provided through the steel t-stub connections. The structural system was modelled in SAP2000 finite element program. The hybrid system is explained in detail and validated using first principles. To evaluate performance of the hybrid core system, a 7-story building was designed using both forced-based design and energy based design (EBD) approaches. Performance of the structure was evaluated using 10 earthquakes records selected for 2500 return period and seismicity of Vancouver. The results clearly served as a good example of the benefits of EBD compared to conventional forced based design approaches.

Effect of welding and complex loads on the high-strength steel T-stub connection

After welding, a heat affected zone (HAZ) is formed in the area near a weld toe. The main microstructure is composed of high-strength steel (HSS) that is not stable at high temperatures. Therefore, it is necessary to investigate whether EC3 formulae based on examining a mild steel T-stub can be used to design an HSS T-stub. In the study, an experiment with two groups of Q690 T-stubs was performed. The results indicate that the EC3 formulae cannot be directly used to design the HSS T-stub. The effect of HAZ was further investigated by performing a finite element analysis (FEA). With respect to the specimens in the study, the factor χHAZ that represents the effect of HAZ is quantified by using the results of the experiment and FEA. The modified EC3 method2 was validated to accurately predict the first yield resistance of HSS T-stub. The T-stub is subjected to combined axial and shear loads. The relation between transversal and axial displacements of the T-stub under combined axial and shear loads was established. The effect of combined axial and shear loads on the connection behavior of the HSS T-stub was examined through the FEA. The result shows that the ductility of the T-stub under combined axial and shear loads is lower than that of the T-stub under axial load. We introduce a factor χCL to propose a formula to predict the first yield resistance of HSS T-stub by considering the effect of combined axial and shear loads.

Behaviours of Spatial Beam-to-Corner Column Joint with T-stub under cyclic loading

The prediction of the behaviour of Spatial joint and plane joint relied on experimental and numerical tests that provide accurate information for the characterization of the beam to Column connection with T-stub. The corner column connections of steel frame as the research object and there are one spatial T-stub connection specimen and one plane T-stub connection specimen. Spatial cyclic load of quasi-static tests and finite element analysis were carried out, of which load was applied to the column. According to the results of quasi-static tests and finite element calculations, difference of joints’ rotational stiffness, hysteretic property, ductility coefficient and energy dissipation characteristics were analysed. It is verified that the mechanical characteristics of spatial semi-rigid joint under spatial load are different from plane semi-rigid joint under plane load.

Finite element analysis on the seismic behavior of fully prefabricated steel frames

This paper presents a method of finite element (FE) modeling and analysis of the seismic behavior of fully prefabricated steel frames with end-plate joints, flexible braces and composite slabs. The main idea and objectives of this paper is to develop a finite element model with high accuracy, good stabilization and acceptable computational costs for the simulation of the cyclic behavior of multi-story steel frames with bolted end-plate joints and concrete slabs. Because of the apparent tension-compression asymmetry of flexible braces, and the complex connection details between slabs and steel structures, as well as the huge number of contact interactions between interfaces, the cyclic behavior of this type of frame cannot be simulated accurately with commonly used line-element models, shell element models, or multi-scale models. A quasi-static test of a full-scale three-story fully prefabricated steel frame under cyclic horizontal loads by the present authors was simulated with the finite element model. Hollow section box columns, I-section beams, end-plates, inner diaphragms and stiffeners were modeled using shell elements; high strength bolts and concrete slab were modeled with solid elements; and flexible braces and rebar were modeled with truss elements. In order to develop a mesh skill to reduce computational costs while ensuring calculation accuracy, several FEM models were built and validated against previous experimental studies: static testing of bolted T-stub connections and bolted tension splices, static and cyclic testing of bolted end-plate steel joints, push-out tests of stud shear connectors, as well as static and cyclic testing of bolted end-plate composite joints. To simulate the “elastic-yield-hardening in tension, and buckling-without capacity in compression” behavior of the flexible braces, a simplified model in ABAQUS based on truss elements was developed and validated against previous tests. Results showed that the proposed FE modeling method could accurately simulate the static and cyclic performance of bolted T-stub connections, bolted tension splices, bolted end-plate steel joints, stud shear connectors, bolted end-plate composite joints and flexibly braced steel frames. Deformation capacity, cyclic behavior, horizontal loading performance, energy dissipation and stiffness degradation of steel frames with bolted end-plate joints, prefabricated slabs and flexible braces could be accurately simulated by this FEM model, providing a practical and accurate modeling method for similar structures. In addition, further research on the structural seismic performance simulation, parametric study and seismic design method could be carried out using the finite element model developed in this paper.

Numerical investigation on strength and failure modes of thread-fixed one-side bolted T-stubs under tension

The failure mechanism of thread-fixed one-side bolted T-stubs under tension was investigated by a finite element model to provide basic knowledge for its potential application in bolted beam-column endplate connection. The finite element model was verified through experimental results by considering four possible reference issues: the T-stub deformation, the force–displacement curve, the failure mode and the yield strength. Studied parameters included the bolt diameter (d), the bolt spacing (s) and the T-stub plate strength (fy). Based on numbers of plastic hinges in the T-stub flange, the failure modes were divided into three categories: Mode 1, complete flange yielding; Mode 2, flange yielding accompanied by bolt failure or hole thread failure; and Mode 3, bolt failure or hole thread failure. Furthermore, modified design equations integrating the potential hole thread failure were proposed to analyze the failure mode and the yield strength of the T-stub connection. Theoretical and numerical analyses showed that the thread hole could provide enough clamping force to fix the high strength bolt, which assured that the one-side bolted T-stub connection would not fail caused by pre-mature thread failure.

Experimental investigation of bolted link-to-column connections in eccentrically braced frames

Link-to-column connections in eccentrically braced frames should transfer the large shear and moment induced in a fully plastic and strain-hardened link. Previous studies have shown that most link-to-column connections fail before achieving the required plastic link-rotation capacity. In this paper, experimental tests were carried out on long link-to-column connections. The purpose of this investigation was to evaluate whether bolted angle connections can be suitable for connecting long links to columns. The T-stub connection, as well as the top and seat angle connection with a web angle, was selected. The test parameters included the strength of the connection which was changed by altering the connection details. The test results indicated that the proposed connections can successfully achieve the desired rotations without any strength loss. Based on the results, it is recommended that the bolted connections whose strength is about the same as that of the link are used to connect long links to columns.

Experimental Investigation of T-Stub Link-to-Column Connections in Eccentrically Braced Frames

Link-to-column connections in eccentrically braced frame should transfer large shear and moment developed in a fully plastic and strain hardened link. Moreover, the connection should allow the link to undergo large plastic rotations. It was observed in previous studies that link-to-column connections are failed before achieving the plastic link rotation capacity. Design of link-to-column connections in seismic-resistant eccentrically braced frames is still an unresolved problem. In this paper, experimental tests are carried out on long link-to-column connections. T-stub connections are used for connecting the link to column. The test parameter is the strength of connection by changing the connection details. The results of the tests indicate that the proposed connections can successfully achieve the desired rotations without any strength loss.

A Novel Approach for Bolted T-Stub Connections

This paper reports an investigation into new connection types and their behaviors determined using full-scale experiments. T-shaped connections were created using the IPE standard profile. The aim of this study was to analyze the influence of T connections based on the IPE standard profile, height of beam to height of T-stub joint (H) of T-stub joints, and lengths (X) of T-stub joints on the behavior of steel connections, in order to provide the necessary data for improving Eurocode 3 and enable efficient use of residue IPE standard profiles and back to the consumption cycle. While the moment resistance values increased with an increase in H from Hmin to Hmax in model groups with X of 126 mm, and the energy dissipation increased with an increase in H from Hmin to Hmax and also with an increase in the lengths (X) of T-stub joints from 54 to 126 mm.