Moment Capacity Of Connections Research Articles

Capacity design assessment of composite reduced web section (RWS) connections

A gap in current design approaches demands explicitly introducing a capacity design approach when designing steel-concrete composite reduced web section (RWS) connections. This paper addresses this gap by presenting test-validated finite element models and parametric investigations, focusing on the presence and absence of composite action over the web opening, the diameter, and the end-distance of the web opening. Additionally, the first-ever comprehensive experimental and numerical database from the literature on bare steel and composite RWS connections is compiled and thoroughly analysed to develop the capacity design assessment for such connections. Both parametric investigations and the database highlight the significance of the capacity design ratio between the connected components in achieving a desirable ductile mechanism. This is crucial, as evidenced by the results: a 15 % increase in the connection's moment capacity led to an average 21 % difference in dissipated energy, favouring the web opening with a diameter of 50do over 80do, in RWS connections with the presence of composite action. The results show that proper consideration of the capacity design approach in designing RWS connections ensures a stable yield mechanism is developed, resulting in the redistribution of global action and capping deformation demands on non-ductile elements. This enhances connections' rotational capacity and ductility by forming the Vierendeel mechanism. Lastly, the paper presents a detailing recommendation for employing RWS connections in both existing and new structures for seismic purposes.

On the Seismic Evaluation of Steel Frames Laterally Braced with Perforated Steel Plate Shear Walls Considering Semi-Rigid Connections

Steel plate shear walls usually do not satisfy the strong-column weak-beam design criteria, leading to larger column sections. On the other hand, rigid frame structures are typically constructed in low-rise to mid-rise buildings built in locations prone to strong earthquakes due to their high flexibility and cost-effective solutions. Overcoming these restrictions to the SPSW system, this paper is dedicated to employing a semi-rigid connection that dissipates energy well and reduces the forces applied to the structure. By using a semi-rigid connection in an adjacent span to the SPSW, the actual flexural capacity of the beam end decreases and, subsequently, improves the performance of the structure in terms of the of the strong-column weak-beam criteria. Thereupon, the impact of the semi-rigid connections on steel frames with SPSWs as a sideway resisting system can be assessed by implementing a numerical study. In this paper, a new methodology for modelling semi-rigid joints is used considering five connections with different moment capacities. Moreover, the influence of three different circular diameters on the behavior of the perforated SPSWs was investigated. To fulfil these purposes, nonlinear dynamic analysis was conducted to assess the reliability of 5-, 10-, and 15-story frames resisted with SPSWs and semi-rigid connections subjected to actual ground motion records. A total of 45 frames were modelled and the obtained results were compared with reference benchmarks. The outcomes of the studies show good agreement with design building code requirements. In addition, the reliable performance of the structure under seismic loads is evaluated. According to the results of the parametric study, the presumed allowable drift leads to obtaining the optimum moment capacity of connection for each model and illustrates the applicability of a new structural system consisting of SPSWs and semi-rigid connections simultaneously.

Numerical modelling of apex connections in cold-formed steel gable frames

Cold-formed steel (CFS) sections have gained acceptance as primary elements in steel frames due to their exceptionally high strength to weight ratio. The main purpose of this research is to study the behavior of the apex joint in portals frame when subjected to monotonic vertical load. Numerical models for apex connections are developed using a finite element program to study the behavior of the connection. The numerical model is first verified by comparing its results with available experimental and numerical results. After the verification, the effect of several parameters on the connection performance was investigated. The parameters included the effect of the connecting gusset thickness and length as well as the effect of the distance between bolts. Moment-rotation relationships for different CFS apex connection numerical models were analyzed. The numerical models showed that the most significant modes of failure were gusset plate or beam web buckling. Increasing the distance between the two connected sections decreased the connection moment capacity, whereas increasing the thickness of the connecting plate enhanced the moment capacity.

Moment capacity of connection with the additional top and seat angles to slab and column panel of cold-formed steel section

Moment capacity of connection with the additional top and seat angles to slab and column panel of cold-formed steel section

Determination of the flexural behavior of steel storage rack baseplate upright connections with eccentric anchor bolts

The baseplate upright connections of the steel storage racks are often attached to the concrete floor by anchor bolts possibly at an eccentric location. Currently available rack design specifications do not provide any guidelines to take account of the influence of eccentric anchor bolt location and do not consider the associated baseplate behavior in the design of such storage rack base connections. The first part of this paper experimentally established the flexural behavior of the baseplate upright connections with eccentric anchor bolts. The experiments considered an enhanced test setup and five groups of three nominally identical test specimens. Influencing parameters such as the baseplate thickness, anchor bolt size, the bracket thickness and the upright thickness were studied. The experimental observations revealed that the baseplate eccentric anchor bolt assembly plays a dominant role on the flexural behavior of the entire baseplate upright connections. The rotational stiffness, the failure mode and the moment capacity of the base connections are strongly intertwined with the eccentric anchor bolt location as well as the baseplate bending behavior. In order to further understand the behavior of such connections, in the second part of the paper, a component-based analytical model is established to predict the initial rotational stiffness and the progressive post yielding rotational stiffnesses of the baseplate upright connections. The moment capacity of the connections is also determined using a deformation limit-based method. The analytical model gives only a 3% underestimation of the initial stiffness and a 3% overestimation of the moment capacity compared with experimental results. The proposed model is suggested to be incorporated in future rack design specifications so that the model can be used by the rack designers to analytically determine the behavior parameters of the eccentric anchor bolted baseplate connections. The rack designers can also use the proposed model to identify the deformation contribution of each individual component and to develop a multi-linear moment-rotation relation of the baseplate upright connections without resorting to the physical experimental tests. Parametric studies were also performed using the proposed analytical model and the influence of relevant parameters had been quantified. Doubling of the baseplate thickness may result in a 11–37% increase in the initial rotational stiffness of the considered baseplate upright connections.

Dual effect of axial tension force developed in catenary action during progressive collapse of 3D composite semi-rigid jointed frames

Catenary action provides more resistance to progressive collapse of semi-rigid jointed steel frames in spite of the axial tension force developed in catenary action stage reduces the moment capacity of the connection. Dual effect of axial tension and its impact on the global structure response is not investigated yet. Limited works have been carried out on beam-column sub-assemblages. This paper studies the dual effect of axial tension developed during catenary action stage of a 3D composite multi-story building with TSD connection taking into account both material and geometry nonlinearity. ND progressive collapse analysis is carried out following the APM recommended by DoD using ABAQUS software. The results show that axial tension improves the progressive collapse resistance by 23% to 36% depending on the column removal locations whereas, the building response increases by 18% to 35% when the connection moment capacity is reduced due to the axial tension. Thus, the designers and engineers have to be cautious while depending on only the positive influence of axial tension developed in the catenary action stage because it simultaneously reduces the connection moment capacity which causes some negative effect on progressive collapse resistance. Also, this study presents a suitable and economical retrofitting scheme by providing bracing on the top floor which enhances the progressive collapse resistance.

The implications of post-tensioning losses on the seismic response of Pres-Lam frames

Since 2010, twelve post-tensioned timber (Pres-Lam) buildings have been constructed throughout the world. In high seismic areas, Pres-Lam technology typically combines unbonded post-tensioning tendons and supplemental damping devices to provide moment capacity to beam-column, wall-foundation or column-foundation connections. Over time creep within the timber elements leads to losses in post-tensioning forces reducing the connection moment capacity. This paper analyses how different post-tensioning loss scenarios, depending on the beam-column joint detailing, impact the building’s seismic response. Two case study buildings were designed and investigated using the Acceleration Displacement Response Spectrum (ADRS) method and Non-Linear Time History Analysis (NLTHA) to predict seismic performance. These buildings were considered to be located in areas of high and low seismic risk, leading to designs with and without the use of damping devices, respectively. The results show that the building with additional damping responded with similar peak displacements, even under extreme loss scenarios. In comparison, when supplemental damping was not used, peak displacements increased significantly with post tensioning losses.

01.05: Experimental and theoretical study of large capacity extended end‐plate moment connection

ABSTRACTOver the years, bolted end‐plate moment connections have been very popular due to the ease of fabrication and erection. The need for large capacity connections with four bolts in one row had become mandatory as a reason of recent complicated structures with large spans and limited available depths. The current research includes an extensive parametric study for the extended large capacity bolted moment connections. For this purpose, three‐dimensional finite element models are prepared using the non‐linear, multi‐purpose, finite element compute package, ANSYS‐11.0. In order to validate the developed finite element model, an experimental program containing five full‐scale flushed and extended, end‐plate connections subjected to bending moment and shear force is performed. The finite element model used throughout the parametric study is verified by comparing its results with the results of the performed experimental study in addition to experimental results recorded by other researchers showing good agreement. The effect of end‐plate thickness, bolt diameter as well as adding horizontal stiffener at two different positions on the connection moment capacity and tension bolt force distribution is studied. Several curves are plotted to show the relation between connection ultimate moments and end plate thickness for different connection configurations. Regression analysis is performed for results and design equations were proposed for each connection configuration.

Robustness assessment of frame structures using simplified beam and grillage models

Simplified analysis methods derived in previous studies are employed for studying the progressive collapse behaviour of steel and composite buildings. A regular frame building is considered and various scenarios of sudden column removal, each affecting different floor areas in terms of geometry and boundary conditions, are applied. Descriptions of the pseudo-static responses of the various constitutive beams are obtained based on both detailed representations of the nonlinear static responses and by applying a new simplified approach proposed in a separate publication. Comparisons between the results of the two methods confirm that the simplified approach is capable of describing behaviour with reasonable accuracy. By employing a simplified multi-level assessment approach that has been previously derived at Imperial College, grillage-type approximations are obtained and used to examine the floor dynamic behaviour for the various column removal cases. It is found that, although the structural response varies depending on the location of the initial damage, substantial connection strength is required in all cases in order to provide resistance to progressive collapse. In addition, for average levels of connection ductility, failure most likely occurs prior to the development of tensile catenary action in the beams, which indicates that the provision of tying resistance may not be effective in enhancing robustness. Therefore, the combined action of flexure and compressive arching in the beams is likely to form the principal collapse resisting mechanism in common practical applications, which confirms similar conclusions made in previous studies at Imperial. The provision of adequate levels of connection moment capacity – in combination with sufficient ductility supply – is, therefore, the most effective way of securing structural robustness.

Semi-rigid composite connection with a partial depth end-plate

The structural behaviour of semi-rigid composite connections with a partial depth end-plate and precast hollowcore slab was investigated by studying moment–rotation diagrams, rotation and bending moment capacities, and induced stresses. The variables considered were the size of the steel beam, the thickness of the lower flange of the beam, the size of column, the number of longitudinal rebars of the concrete slab, and the thickness of the partial depth end-plate. A parametric study was undertaken using the non-linear, three-dimensional, finite-element method, with monotonic loading applied to connections. The results obtained indicate that the thickness of the partial depth end-plate has a great effect on the bending moment capacity of the connection. When the beam size was varied, three failure modes were observed. The variation of beam depth had the greatest effect on the bending moment and rotation capacities. Reduction of the beam lower flange thickness considerably affected the rotation capacity and changed the failure mode in the connection. When the number of longitudinal rebars was increased, the bending moment capacity increased but the rotation capacity showed a slight decrease. For the column, the variation in web thickness had the largest effect. It was shown that it is possible to use a simplified method to predict the bending moment capacity of a semi-rigid composite connection.

HSS-to-HSS seismic moment connection performance and design

Abstract Hollow structural sections (HSS) provide an alternative to typical wide flange sections in low-rise seismic moment resisting frames. Their beneficial strength-to-weight ratio as well as bending, compression, and torsional resistance increases the versatility of moment frames and potentially improves performance under earthquake loads. With an understanding of current design requirements for seismic moment connections and static HSS-to-HSS connections, 39 fully welded unreinforced HSS-to-HSS connections are explored through finite element analyses. However, performance is limited due to column face plastification and inability to develop the plastic moment capacity of the beam. To rectify this problem, 24 through plate and 24 external diaphragm plate HSS-to-HSS moment connections are analyzed. Several important geometric parameters, such as the beam width–column width ratio, beam thickness–column thickness ratio, plate length, and plate thickness are considered to understand their effect on the connection moment capacity and sources of inelastic rotation. The through plate and external diaphragm reinforcement greatly improve the connection behavior moving yielding away from the column face and into the beam member. The results from the reinforced connections are used in combination with current seismic design provisions to develop a design procedure that optimizes the performance of these connections. The reinforced connections can be detailed to develop plastic hinging in the HSS beam member while minimizing the likelihood of a non-ductile weld failure.

Experimental testing and simulation of bolted beam-column connections having thick extended endplates and multiple bolts per row

Retrofit of existing steel buildings often requires strengthening of the connection regions. One common connection, the bolted beam-column connection, is often strengthened in design using stiffened extended endplates, or with continuity plates welded between the column flanges. In a retrofit scenario, adding stiffeners to the endplate is difficult due to the concrete slab and metal deck, and excessive field welding of continuity plates may be uneconomical. Simplifying retrofit efforts, and for economy, connection strength may be improved by simply adding more bolts to the connection. Current code methods, broadly generalized to all connection configurations, are currently based on component experiments having only one bolt on either side of the column web. This study experimentally investigates strengthening of bolted beam-column connections, having no column web stiffeners, using more than one bolt on either side of the column web. Six full-scale bolted beam-column connections are tested, representing exterior beam-column connections (beams attached to only one column flange). Connections with both extended and flush endplates are considered. Two column sections (HE300A and HE300B) are tested along with HE300B beams creating both equal-column-beam, and weak-column strong-beam scenarios. Analytical simulations provide insight into local connection demands, and experimental results are compared with current code methods. The experiments indicate that closer inner-bolt spacing relative to the column web increases connection moment capacity but decreases rotation capacity (connection ductility) due to increased bolt prying forces from column flange distortions. The outer bolt of multiple-bolt-per-row configurations contributes very little to the connection resistance when column web stiffeners are not considered. With the exception of specimen T-3B which failed through bolt-thread shear after 0.02rad, all connections with multiple bolts per row still achieved rotations greater than 0.06rad. The Eurocode 3 component method and adapted Eurocode 3 procedures conservatively predicted the connection strength of each test specimen, including weak-column strong-beam assemblies, and accurately identified the initial connection limit states.

Performance of the PR connections under combined Axial-tension and moment loading

The inherent moment capacity of bolted top-seat angle connections with double web angles (TSDW), categorized as partially restrained (PR) connections according to AISC-LRFD specifications, can be considered in analyses of semi-rigid connections especially when an accurate analysis of such fames is desired. However, in some cases, developed internal forces in the frame elements may affect the connection behavior, considerably. Axial tension force is one of such internal forces that may be imposed on frame connections in some cases such as construction imperfections, seismic loading or under large deflections of the catenary action during the progressive collapse of the semi-rigid frames. This study aims at the effects of the axial tension force on the performance of the bolted TSDW angle connections using nonlinear finite element method (FEM). The obtained results show that the axial tension force reduces the connection moment capacity and stiffness, considerably. Based on the obtained moment-rotation curves, affected by this particular loading type, equations are proposed to estimate the reduction rate of the connection stiffness and moment capacity.

Fracture Moment Strength of Reduced Beam Section with Bolted Web Connections

Reduced Beam Section (RBS) moment connections are developed for Special Moment Resisting Frames (SMRF). According to the beam web attachment the column flange RBS connections are classified into Reduced Beam Section with Bolted web connections (RBS-B), and the Reduced Beam Section with Welded web connections (RBS-W). Beam flanges are welded to the column. Regardless of different web attachment details in RBS-B and RBS-W connections current design procedures (FEMA 350) assumes that they could develop plastic moment of the beam gross section. In current design procedures, RBS-B connections should provide the sufficient strength that can reach the plastic moment capacity of the connected beam. However, some experimental researches reported that the beams in RBS-B connections fractured before the connection reached its plastic moment capacity. Such undesirable fracture shows that RBS-B connections have less strength than RBS-W connections. And if RBS-B connections designed in current design procedures, it might fail in a brittle manner and not satisfy SMRF due to undesirable fracture. Thus, this study develops a new set of equations for accurately computing the moment strength of RBS-B connections. The proposed strength equation accurately predicts connection moment capacity for RBS-B connections.

Behavior of Unbonded, Post- Tensioned, Precast Concrete Connections with Different Percentages of Mild Steel Reinforcement

This paper presents the results of tests performed on post-tensioned, precast concrete moment-resisting, beam-column connections containing different mild steel reinforcement contents. In the experimental program, five hybrid connections were tested under displacement-controlled reversed cyclic loading. The main variable was the mild steel's percentage of contribution to the flexural capacity of the connection, ranging from 0% to 65% of the connection's moment capacity. Each hybrid connection was compared with the test result of the reference monolithic subassembly in terms of connection strength, stiffness degradation, energy dissipation, and permanent displacement. The objective of this study was to determine the effect of mild steel reinforcement content on the behavior and performance of post-tensioned, precast concrete hybrid connections. The response of post-tensioned, precast concrete hybrid connections approached that of the monolithic subassembly as the mild steel reinforcement content increased. Connection capacities were well predicted by the joint gap-opening approach. The design assumptions of hybrid connections are best satisfied with a 30% mild steel reinforcement contribution to the connection's flexural capacity.

설계변수에 따른 플랫플레이트-기둥 접합부의 강도산정모형

In the present study, a numerical analysis was performed for interior connections of continuous flat plate to analyze the effect of design parameters such as column section shape, gravity load and slab span on the behavioral characteristics of the connections. For the purpose, a computer program for nonlinear FE analysis was developed, and the validity was verified. Through the parametric study, the variations of shear stress distribution around the connection were investigated. According to the result of numerical analysis, as the length of the cross section of column in the direction of lateral load increases and gravity load increases, the effective area and the maximum shear strength providing the torsional resistance decrease considerably. And as the slab span loaded with relatively large gravity load increases, the negative moment around the connection increases and therefore the strength of connection against unbalanced moment decreases. By considering the effect of design parameters on the strength of the connections, the effective shear strength to calculate the torsional moment capacity of connection was proposed and the effectiveness of the proposed shear strength was verified.

Application of steel channels as stiffeners in bolted moment connections

This paper proposes a stiffening method to meet some architectural needs. This method uses bolted channels as alternatives to both continuity and doubler plates in bolted moment-resistant beam-to-column connections. The present study investigates the performance of channels as stiffeners to: increase yield load in the tension zone of connection, gradually increase overall moment capacity of connection, and avert shear failure of the column web panel zone. We conducted experiments to examine the tension region of the connection loaded from T-stubs. The moment capacity of full connection was predicted by considering T-stub idealization and shear effects on the column web panel. T-stub tensile behavior and overall connection behavior were also monitored using three-dimensional finite element simulations in ANSYS simulation software because this problem is three-dimensional in nature. Effects of geometrical and material non-linearities on interaction among connecting members should be clarified. This study showed marked strength improvement in connection by use of channels. The performance of channel stiffeners was examined through comparison of results.

Seismic Performance of Pile-Wharf Connections

Imports and exports are essential to our economy, but the wharf structures that accommodate this activity are susceptible to earthquake damage. Wharves are pile supported structures, and the pile-wharf connection is an essential element of their seismic performance. Either precast prestressed concrete piles with moment-resisting connections or steel batter piles are used to provide lateral resistance, but precast concrete piles are more common. Little research has been performed on the seismic performance of these precast concrete pile-wharf connections. Eight experiments evaluating the seismic performance of moment-resisting precast concrete pile-wharf connections are described. The test specimens simulate the wide range of practice presently noted in wharf design. These connections tolerate large cyclic inelastic deformations, but they also show significant deterioration in resistance and stiffness. Extended pile connections are used when the pile is driven below deck level. Precast concrete pile connections are stronger than extended pile sections, but they degrade more quickly. Axial load on the pile also increases connection moment capacity but results in greater deterioration in resistance. Analysis shows that this degradation in resistance significantly reduces the inelastic pushover resistance and increases the inelastic dynamic response demands of the system.

Behaviour of composite haunched beam connection

This paper is concerned with the behaviour of steel–concrete composite haunch connections. Experiments were carried out to investigate the moment-rotation characteristics and ultimate moment capacity of these connections. Details of the experiments giving information on test specimens, instrumentation, test set-up and test procedures are described. Results obtained for connection moment capacity, rotation capacity and failure modes are presented. It is found that through proper design and detailing, these connections display the characteristics of a rigid connection.

Toward design office moment-rotation curves for end-plate beam-to-column connections

A semi-analytic method to model moment-rotation curves for unstiffened extended end plate connections is presented. Two physically based parameters; connection initial stiffness and connection moment capacity, and one experimentally based parameter are used in a three-parameter power model. Good correlation between the proposed model and experimental results is shown. The proposed method is then simplified, resulting in moment-rotation curve modeling suitable for design office environments.