Extended End Plate Connections Research Articles

Performance of short links with flush and extended end plate connections using FEM analysis

AbstractEccentrically braced frames are commonly used as a seismic resistant system, due to the good balance of stiffness and ductility. Bolted links have been proposed in the past to allow replacing the damaged dissipative components following a strong earthquake. The goal of this research work is to investigate the influence of the connection type on the performance of bolted links using the Finite Element Analysis. Numerical models of links are first calibrated using past experimental tests. Modelling criteria adopted to replicate the experimental behaviour of the links highlighted in the tests are reported. The achieved results obtained regarding a flush end plate bolted link and an extended end plate bolted link with different lengths are then used as benchmark to assess the influence of the link length and type of connections adopted on the response of the links. The Finite Element Method is used to investigate alternative solutions to the tested ones. Finally, the investigated options are compared to determine the advantages and disadvantages of each solution.

Seismic Performance Evaluation of Moment Resistance Connection by Load Velocity.

AbstractThe seismic performance of beam‐column connections is typically evaluated using a loading protocol specified by codes such as AISC. This protocol involves applying incremental and repeated loads at a specified speed to reach a target rotation angle, with a low load velocity of about 0.5 mm/s to 1.0 mm/s. However, testing at such a low load velocities may not fully account for brittleness breakdown due to factors such as a reduction in material toughness and a decrease in maximum deformation rate caused by stress concentration in vulnerable areas at high load velocities.Therefore, it is important to verify the seismic performance of connections, including their plastic deformation ability, under the influence of dynamic loads with high velocities, such as those experienced during an earthquake. We conducted a static and dynamic experiment on welded connections and extended end plate connections to analyze the effect of load velocity on connections behavior.Our results showed that increasing the load velocity reduced the strength of the connection, its plastic deformation capacity, and energy absorption capacity. These findings confirm that load velocity can significantly affect the seismic performance of connections and suggest that the current loading protocol may not fully capture the connection behavior under dynamic loads.

Numerical assessment of an enhanced stiffened extended end-plate joint for composite frame structures

This paper presents the numerical assessment of a novel enhanced Bolted Stiffened Extended End-Plate (BSEEP) connection for steel frames with composite beams and H-shaped columns in the strong direction. Strain demand is a critical local response that directly controls rupture initiation, and it is more crucial in composite beams since the neutral axis shifts upwards due to the composite action. The proposed connection, called URBS-BSEEP, employs a reduced section in the beam upper flange to mitigate the strain demand problem and provide a stable and symmetric plastic hinge in the desired location. Nonlinear FEM is employed to study joint cyclic behavior. Eleven specimens are designed to compare the proposed connection with existing configurations and to investigate the effects of the slab isolation from the column, shear stud removal, reduced section geometry, and slab thickness. Hysteresis curves, ductilities, failure modes, strain profiles, and energy dissipation capacities are compared. The results indicate the superior performance of the connection compared to the conventional counterparts.

Cyclic behavior of a novel bolted beam-to-box column connection with reduced beam section

The present research investigates the seismic performance of innovative subassemblages in built-up box columns with reduced beam sections (RBS) technique through the finite element (FE) analysis method. The configuration of the subassemblages additionally benefits from having an extended endplate connection, which allows the subassemblages to be erected quickly and at a lower cost. So far, there has been very little detailed research on RBS moment connections in box columns with extended bolted endplates due to the closed shape of box columns and difficulty of accessing the column inside for developing a reliable load path. To solve these complexities, a novel configuration called “Reduced Bolted Extended Endplate accompanied by Stub Beam (Reduced BEEP-SB)” is introduced. The new load transfer mechanism of the subassemblages is described. Furthermore, 35 various exterior beam-to-column subassemblages are modelled in ABAQUS/STANDARD FE analysis software and tested under the connection qualification cyclic loading conditions. The results indicate that the proposed subassemblages can push away plastic hinge formation at an appropriate distance from the column endplate interface. Also, the flexural capacity of subassemblages is approximately 10–20% higher than the beam plastic moment capacity. Moreover, the results in terms of moment-rotation curves and strain in critical sections show that the models without continuity plates could satisfy the connection qualification criteria. It is noteworthy that the accuracy of the introduced models was validated via two experimental models.

Methodology and Application of Ductile Damage Modeling on Double Tee and Extended Endplate Connections

Methodology and Application of Ductile Damage Modeling on Double Tee and Extended Endplate Connections

Cyclic Response of Sloped Extended End-Plate Moment Connections

Bolted extended end-plate (BEEP) moment connections are extensively recommended in design standards to be used as a prequalified beam-to-column connection in steel portal frames and special moment frame buildings. These standards assume that in such a connection, the beam is perpendicular to the steel column or that the slope angle of the steel beam is very small. To expand the engineering applications of BEEP connections in large-slope angle buildings, in this study, three one-sided specimens at half scale with 0°, 15°, and 30° slope angles, respectively, were designed and tested under cyclic loading. All dimensions of these specimens were identical, except the slope angles of their steel beams. The experimental results showed that the maximum rotation angles of these sloped BEEP connections exceeded 0.05 rad, and they were remarkably larger than those of other types of sloped rigid-moment connections tested by Mashayekh and Uang. However, the force concentration that occurred in the flange at the heel location was similar to that observed by them, and it led to the development of brittle fractures. Particularly, with the increase in the slope angle, the force concentration tended to become more severe. Three strengthening schemes for reducing the force concentration and enhancing the deformation capacities of the sloped BEEP connections subjected to the extremely rare earthquake, i.e., less than 2% probability of exceedance in 50 years, were evaluated using the finite element approach. These were Scheme I: stiffening the rib in the acute-angle zone, Scheme II: employing a reduced beam section (RBS) connection, and Scheme III: forming a curved web cut in a non-RBS beam. The analytical results showed that the three schemes decreased the von Mises stress level in the acute-angle zone of the connection web. Scheme I enhanced the initial rotation stiffness, flexural strength, and deformation rotation capacity. For Scheme II, a RBS configuration was employed, which effectively improved the connection rotation capacity, whereas it decreased the flexural strength of the sloped BEEP connection. Scheme III without a reasonable design led to a degradation of the hysteretic performance, moderate rotation capacity, and low flexural strength. Therefore, Schemes I and II leading to much better seismic behavior than Scheme III are recommended.

Cyclic and monotonic performance of unstiffened extended end-plate connections having thin end-plates and large-bolts

This study presents the findings of comprehensive numerical and experimental programs on unstiffened extended end-plate connections (UEECs) having thin plates and large sized bolts. The main goal of the research program is to analyze the effects of variables influencing the capacity of these connections. Six specimens were subjected to cyclic and monotonic loading to achieve this goal. For the experimental part, the thickness of end-plate was chosen as the variable. The thickness of end-plates was selected to ensure failure modes governed by the bending capacity of end-plates. A comprehensive numerical study consisting of 156 finite element models where the parameters are I-section types, width and thickness of end-plate, edge distance, distance from flange to bolt row, bolt diameter and weld thickness was performed. The results showed that the connections with thin end-plates can perform high ductility and strength. Moreover, the design methods given by AISC 358-16 and EN1993-1-8 conservatively predict the plastic moment capacity of UEECs. According to numerical findings, the average ratios of actual to estimated plastic moment capacity by AISC 358-16 and EC3:1-8 are 2.77 and 3.13, respectively. These ratios alter to 3.70 and 3.93 for the experimental results. The yield line mechanism and the spacing between the plastic hinges are to cause this underestimate. An expression for the observed yield line pattern is developed to estimate the plastic moment capacity more correctly. The actual to estimated plastic moment capacity ratios according to proposed expressions are averagely 1.23 and 1.29 for the outcomes of the experimental and numerical study, respectively.

Artificial Neural Network–Based Predictive Tool for Modeling of Self-Centering Endplate Connections with SMA Bolts

Endplate moment connections with shape memory alloy (SMA) bolts provide self-centering for the seismic resilience of structures. Predicting the self-centering response of these new beam–column connections, which have not been codified yet, requires conducting experimental tests or detailed continuum finite-element simulations. Computationally efficient predictive tools are needed to facilitate the analysis, design, and assessment of self-centering connections and moment frames. In this paper, artificial neural networks (ANNs) are used to develop a MATLAB tool for predicting the moment-rotation backbone and self-centering response of extended endplate connections with SMA bolts. As the input for the neural networks, the predictive model development employs a design database of response parameters from 72 finite-element (FE) models and experimental tests of seven beam–column connection specimens. Neural networks are trained for seven response parameters, and the trained networks are used to develop a graphical user interface (GUI). The coefficient of determination for the trained ANNs is in the range of 0.92 to 0.99, indicating acceptable prediction accuracy. Furthermore, optimization studies using a multiobjective genetic algorithm are performed, seeking the minimization of material use (steel and SMA) and improved connection-response characteristics (i.e., stiffness, strength, and ductility). A phenomenological model of SMA connections is also developed in OpenSees. The use of the ANN-based predictive tool for accurate and efficient modeling of SMA-based connections and self-centering moment-resisting frames is illustrated. The computation time for predicting the moment-rotation response of a typical SMA connection is significantly reduced from seven hours in ANSYS to only three minutes in OpenSees while providing the same level of response prediction accuracy. Furthermore, the optimization results are confirmed by performing nonlinear pushover and response history analyses.

Strengthening strategies against the progressive collapse of steel frames with extended end-plate connections

In this paper, a new type of the strengthened strategy for the limited anti-collapse capacity of extended end-plate connections (EECs) is proposed. Bending stiffened steel plates (BSSPs) were placed in the joint region to form a new type of strengthened extended end-plate connection (SEEC). First, the geometric motion characteristics of the BSSPs on the tensile and compression sides of the joint are described through theoretical analyses, and the improvement mechanism of the anti-collapse performance of the SEEC is given. Subsequently, using the verified numerical model, nine groups of parameters affecting the ultimate rotation of the EEC were analyzed, and the calculation formula for the ultimate rotation of the EEC was given via nonlinear fitting based on its numerical results. The numerical analysis example shows that the process of resistance development in the SEEC comprises three stages: elastic, transition, and improvement. Among them, the BSSP works well with bolts and end plate, which makes the SEEC obtain a more significant improvement stage and proves that the BSSP design process is reasonable. Finally, the main parameters a1, b1, and the thickness of the SEEC, were analyzed and suggested using parametric analysis.

Simplified Modelling of Failure in High Strength Bolts under Combined Tension and Bending

Bolted connections are widely adopted in steel structures and their behaviour affects to a large extent the global response of the system. High-strength bolts of type HV are commonly employed. Under pure tension, these bolt assemblies usually fail by thread stripping. However, it was observed experimentally that, under combined tension and bending, the failure mode changes to fracture of the shank. The former loading condition commonly occurs in the case of thick extended end plate connections and the latter in the case of flush end plates. In order to analyse the behaviour of the structure, the finite element method (FEM) is usually employed. While there is a wealth of information on FEM modelling of bolts for standard loading conditions (e.g., tension), the authors are unaware of a model able to replicate both tension-only and combined tension and bending conditions. In this paper, a simplified approach to be used in the framework of FEM is proposed to model the behaviour of high-strength HV bolts which can replicate the failure mechanism of bolts under tension only and combined tension and bending. The bolt assembly is modelled with continuum elements, supplemented by a non-linear spring connecting the nut to the bolt shank. The spring captures the stiffness, resistance, and ductility of the bolt-to-nut threaded connection, reproducing the experimentally observed failure mode in the case of pure tension conditions. A simplified damage model is applied to the continuum finite elements used to model the bolt, which replicates shank failure under combined tension and bending as a result of large local stresses and strains occurring under these conditions. The proposed model captures with good accuracy the actual behaviour of high-strength HV bolts under tension only as well as under combined tension and bending.

Cyclic and monotonic performance of stiffened extended end-plate connections with large-sized bolts and thin end-plates

Cyclic and monotonic performance of stiffened extended end-plate connections with large-sized bolts and thin end-plates

Bolt Pre-tension Effect on Performance of Bolted Extended End-plate Moment Connections under Cyclic Loading

The most important structural part of steel structures is the connections of the building frame. Tests conducted by the American Steel Institute have led to the introduction of prequalified connections, which is a good reference for designing connections in steel structures. In this paper, four bolted stiffened and unstiffened extended end-plate connections have been studied by numerical analysis with ABAQUS software. In this study, to examine the effect of bolt pre-tension rarely studied, a coefficient of pre-tension force, introduced based on the Iranian Steel Structures Design Regulations as well as the US Steel Design Regulations, has been considered. These connections have been modeled cyclically and in a displacement control manner. The cyclic behavior of the connections, dissipated energy, the resisting moment as well as the stress and strain distribution in the connection have been investigated. According to the results, by creating a pre-tension force in the bolts, the resisting moment of the connection would increase. The rate of growth of this resistance in the unstiffened connections was greater than that of the stiffened connections. The maximum increase in resistance was about 27% for the unstiffened connection and about 25% for the stiffened connection. The dissipated energy for the connections also increased with the increment of bolt pre-tension. The energy dissipation incremental rate was enhanced to a maximum of about 31% for the unstiffened connection and up to a maximum of about 24% for the stiffened connection.

Seismic performance of thread-fixed one-side bolts bolted extended endplate connection to HSST column with internal strengthening components

This paper presents experimental results of the seismic performance of the Thread-fixed One-side Bolts bolted Endplate Connection to Hollow Square Steel Tube column (TOBEC-HSST) with internal strengthening components. Five specimens were tested under cyclic loading. The main variable parameters affecting the seismic behavior of specimens were the internal strengthening structure types (i.e. the polygonal steel tube without inner stiffener, or with the horizontal or vertical stiffener) and the extended endplate types (i.e. with or without the endplate stiffeners). The failure modes of connections were observed, the moment-rotation hysteretic response and the strain distribution of connections were obtained. Besides, the rotation ability and ductility, the degradation of strength and rigidity, and the energy dissipation capacity were analyzed and compared, which were affected by the strengthening measures. The introduction of the endplate stiffeners can improve the overall rigidity of the joint region and sufficiently develop the energy dissipation capacity and ductility of the connections, and the contribution from the inner stiffener in the internal strengthening polygonal steel tube can also enhance the seismic performance of the connections. In addition, the rotations at the failure of the connection were larger than 30 mrad, which satisfied the ductility limitation requirement in reference to FEMA-350, revealing a potential to the application in seismic steel structures.

Behaviour of Extended Endplate Connection with Mild and High Strength Steel

This paper uses the multi-purpose software ABAQUS to create a three-dimensional finite element model of an extended end plate connection to analyze and compare the behaviour of mild steel and high-strength steel endplate connections. The numerical model's results are calibrated against reported experimental results to ensure that it can simulate and analyze both the overall and detailed behaviour of different types of bolted endplate steel connections. The results of the study compare and analyze the moment-rotation relationships and the behaviour characteristics of the connection with mild steel and high strength steel. Upon validation of the FE models' parametric studies were performed to investigate the effect of different parameters on the behavior of bolted extended end-plate connection. Therefore, the geometric parameters are selected and varied within the comprehensive practical ranges of extended end-plate connections.The parameters varied for the parametric studies include the thickness of the end plate, bolt diameter and steel grade of the endplate.

Surrogate models for endplate beam-column connections with shape memory alloy bolts

This paper presents the development and validation of moment-rotation backbone curve parameters for self-centering steel endplate connections with superelastic SMA bolts. In terms of influential design factors, surrogate models of response parameters are proposed using detailed finite element models of self-centering beam-column connections and statistical analysis of response parameters. The predictive surrogate models are useful for characterizing the connection backbone and self-centering response, which is essential for the performance-based design and assessment of extended endplate connections equipped with SMA bolts. Through a verification study, the accuracy of predictions using the proposed models is confirmed. The proposed surrogate models are used to assess the fragility of SMA-based beam-column connections. The results demonstrate that endplate beam-column connections with SMA bolts can provide an acceptable level of deformation capacity. Furthermore, it is found that larger diameter SMA bolts and smaller depth beam sections can reduce the probability of experiencing SMA bolt fracture by 31% and 77%, respectively.

Post-earthquake fire resistance of bolted end-plate connection joint with end-plate and web stiffeners

This paper aims to study the fire resistance of the extended end-plate connection (EEPC) joints under post-earthquake fire (PEF) by considering different earthquake damages, which can reduce the fire resistance of the EEPC-joints. The effectiveness and accuracy of the computation models were verified by using the existing test results. Then, the fire resistance of 8 kinds of the EEPC-joints with different stiffening strategies were compared and analyzed. The results showed that the extended end-plate connection with pentagon end-plate stiffeners and web stiffeners had the best fire resistance and was selected to conduct a parametric analysis under PEF. In order to investigate the effects of different parameters on the fire resistance of the EEPC-joints under PEF, 25 computational models of the extended end-plate connections with pentagon end-plate stiffeners and web stiffeners were established. Then, a parametric study was performed by considering the column flange width-thickness ratio (α), beam web height-thickness ratio (β), ratio of beam end-plate stiffener thickness to beam end-plate thickness (γ), ratio of the thickness of column web stiffeners to the thickness of the column end-plate (λ), ratio of the thickness of beam end-plate to column end-plate (ξ), the thickness of non-intumescent fire retardant coating and damage variable (D~). The results showed that damage variables had significant influence on the fire resistance of the EEPC-joints under PEF. The findings of this study can provide the needed reference for fire resistance design of the EEPC-joints under PEF.

Hysteretic performance of stainless steel double extended end-plate beam-to-column joints subject to cyclic loading

This paper focuses on the hysteretic performance of stainless steel beam-to-column joints with double extended end-plate connections under cyclic loading. Six full-scale joint specimens were fabricated, including three interior column joints and three exterior column joints. Two stainless steel grades — austenitic grade EN 1.4301 and duplex grade EN 1.4462, and one carbon steel grade Q345B were considered. A4-80 stainless steel bolts and grade 10.9 high strength steel bolts were employed to assemble the joint specimens. The cyclic loading tests were conducted using the loading protocol set in Chinese standard JGJ/T 101. The force versus displacement (F-Δ) hysteresis curves were recorded, and the failure modes, the ductility, the strength and stiffness degradation, and the energy dissipation capacity of the tested joints were analysed and discussed in detail. Empirical hysteresis models were developed and calibrated against the recorded hysteretic curves and energy dissipation capacities of the tested joints. The experimental results involving the initial rotational stiffness values and the moment resistances were further utilised to evaluate the accuracy of current design provisions codified in EN 1993-1-8, ANSI/AISC 358 and GB 51022. The comparison shows that the development of accurate design guidance accounting for the pronounced strain hardening of stainless steels is warranted.

The plastic and the ultimate resistance of four-bolt extended end-plate connections

Widely used design guidelines and specifications provide methods to calculate plastic resistance of end-plates considering yield line mechanisms. Experiments reported to date showed that the ultimate resistance of end-plates can be considerably larger than its plastic resistance due to strain hardening. Using the ultimate strength in design can be a viable and cost-effective option; however, limited studies exist on quantifying the ultimate strength. In this paper, a database of four-bolt extended end-plate moment connections was developed. The capacities of these connections were calculated using AISC Design Guidelines and EN1993-1-8. The results showed that the plastic resistances of connections are on average 29% greater than the capacities calculated using the AISC Design Guidelines. On the other hand, the test-to-predicted ratios were found to have an average of 1.08 for EN1993-1-8. The ratios of the ultimate resistance to the calculated plastic resistance are 2.07 and 1.73 for AISC and European approaches, respectively. A numerical study was undertaken to propose modified design expressions for the plastic resistance which are compatible with AISC Guidelines. Furthermore, the ultimate resistance of end-plates was quantified. Stiffened and unstiffened T-stub models were analyzed using the finite element method. Expressions based on yield line mechanisms were developed to calculate the plastic and ultimate resistance. The evaluations showed that the averages of the test-to-predicted ratios are 1.06 and 1.17 for the plastic and ultimate resistance respectively when the proposed expressions are used.

Investigating the behaviour of steel end-plate connections with shape memory alloy bolts

Conventional extended end-plate connections with normal high-strength steel (HSS) bolts show considerable residual deformation following an earthquake. The application of shape memory alloys (SMAs) has recently been considered in seismic regions because of their capabilities, such as the ability to tolerate cyclic deformations and dissipate energy. In this paper, extended end-plate connections equipped with SMA bolts are investigated. A hybrid extended end-plate connection utilising SMA bolts only for the outer rows and conventional HSS bolts for the remaining rows is a new and viable alternative to existing connections. Finite-element models of connections with different bolt lengths and pre-stressing levels have been developed using Ansys software. The cyclic performance of the models has been assessed and compared. Results indicated that conventional and hybrid connections have better capabilities in energy absorption compared to SMA connections. The hybrid connections and also connections with 69 mm long SMA bolts are classified as high-ductility connections according to the American Institute of Steel Construction (AISC). Increasing pre-stressing over 50% fy has no significant effect on the cyclic performance of connections.

Effect of bond and bidirectional bolting onhysteretic performance of through bolt CFST connections

Through bolt connections in Concrete Filled Steel Tubes (CFSTs) has been proved to be good in terms of seismic performance and constructability. Stiffened extended end plate connection with full through type bolt helps to avoid field weld altogether, and hence to improve the quality of joints. An experimental study was conducted on the hysteretic performance of square interior beam-column connections using flat extended end plates with through bolt. The study focuses on the effect of the bond between the tie rod and the core concrete on the cyclic performance of the joint. The study also quantifies how much the interior joint is getting strengthened due to the confinement effect induced by bi-directional bolting, which is widely used in 3D moment resisting frames. For a better understanding of the mechanism and for the prediction of shear capacity of the panel zone, a mathematical model was generated. The various parameters included in the model are the influence of axial load, amount of prestress induced by bolt tightening, anchorage, and the concrete strut action. The study investigates the strength, stiffness, ductility, and energy dissipation characteristics. The results indicate that the seismic resistance is at par with American Institute of Steel Construction (AISC) seismic recommendations. The bidirectional bolting and bond effect have got remarkable influence on the performance of joints.