Reduced Beam Section Connections Research Articles

Analytical and numerical investigation of the seismic behavior of tubular web reduced beam section connections

AbstractThe reduced beam section (RBS) connections in steel structures are widely used to achieve sufficient ductility and avoid creating brittle failures in moment‐resisting frames. Compared to other types of connections, conventional RBS connections have the potential to reduce moment capacity and induce larger lateral deformation in the structure. In order to resolve this problem, novel forms of RBS connections have been proposed in recent years, such as tubular web RBS connections, which have shown a desirable performance under various loading conditions in previous studies. Therefore, this study conducted an analytic and numerical investigation of this connection under seismic loading. In this regard, the first step is to introduce the analytic equations related to the structural properties and stability of the reduced beam with the tubular web. Using these equations, a comprehensive procedure for the design of the tubular web RBS connections is presented. After that, a numerical model of the tubular web RBS connections is created and then analyzed under cyclic loading using the finite element method in ABAQUS software. Based on the results of this simulation, the suggested connection meets the criteria of valid international standards and can be used in the special moment‐resisting frame. In order to assess the impact of using the proposed connection in moment‐resisting frames, the performance of two 2D moment‐resisting frames with this connection is studied. This study shows that the maximum percentage increase in relative displacement caused by using tubular web RBS connections is 1.68%, whereas this figure rises to 10.6% when conventional RBS connections are used. Therefore, the designers can use tubular web RBS connections instead of conventional RBS connections to increase the lateral stability of the structure and control its lateral deflection due to the seismic loadings without having to increase the dimensions of the frame elements.

Research on the anti-collapse performance of steel frame structures with infilled walls in the form of reduced beam sections connections

Steel has more deformation capacity and resistance to compression buckling than concrete materials, which providing steel frames a distinct edge in preventing collapse. This study examines the anti-collapse performance and mechanism of steel frame structures with infilled walls in the form of reduced beam section connections. It also examines the effects of wall thickness, frame aspect ratio, and connection control size on performance and addresses the applicability of current code formulas in the early deformation of the structure. The study discovered that steel frame structures with infilled walls in the form of reduced beam section connections can, during the failure stage, enhance the infilled wall's contribution to the collapse bearing capacity, thereby stimulating the structure's potential performance, in contrast to those with infilled walls in the form of non-reduced beam section connections. Due to the supporting effect of the double strut that forms inside the infilled wall during the failure stage, steel frame structures with infilled walls that have non-reduced beam section connections have higher deformation capacity than corresponding pure frames; however, this effect also decreases the deformation capacity of the structure with reduced beam section. Furthermore, the infilled walls cause the structure to collapse in a same way across a range of aspect ratios, yet their contribution to the structural bearing capacity differs across these same aspect ratios. It is noteworthy that altering the local connection control size can greatly enhance the structure anti-collapse performance, even in unfavorable aspect ratio scenarios. The study also discovered that the bearing capacity of the structure studied in this paper was overestimated by the FEMA356-2000 code and the MSJC code, which were used to predict the initial bearing capacity of infilled frames. The former's overestimation reaches a maximum of 39 %, while the latter's prediction is only accurate within a limited range of aspect ratios. Furthermore, the formula by Qian and Li, which has a maximum error of 9 % in bearing capacity prediction within the standard range of aspect ratios, is better appropriate for the failure mode of the structure described in this study.

Evaluation of progressive collapse resistance performance of steel OMF with WCPF connections

A welded cover plated flange (WCPF) connection, which is a pre-qualified connection detail improving a weak weld access hole and the ductility of a welded unreinforced flange-bolted web (WUF-B) connection, has a simple and efficient advantage in construction. In this study, a new modelling approach of the WCPF connection by employing 1-D element was proposed for the evaluation of progressive collapse resistance capacity performance. The model was developed by substituting the average width of trapezoidal shapes of cover plates welded to the top and bottom flanges and by assessing the equivalent flange thickness based on the moment of inertia. The proposed model was verified through comparisons with experimental and 3-D numerical results, showing discrepancy within 5.7%. To evaluate the performance of the WCPF connection, a prototype structure was adopted from the previous study for the appraisal of the WUF-B and reduced beam section (RBS) connections. The alternative load path method was performed using an energy-based approximate analysis considering the dynamic effect of sudden column loss. The performance of the structure was evaluated in terms of structural robustness and sensitivity. Furthermore, the results were compared to those of the structures with the WUF-B and RBS connections analyzed in the previous study. The structure with the WCPF connections showed 33% more improved structural robustness and 11% less sensitivity to progressive collapse when one column was removed. In a two-column removal scenario, only the structure with WCPF connections indicated to have proper progressive collapse resistance capacity. The WCPF connection was deemed more reliable than WUF-B and RBS ones.

Seismic Performance and Calculation Method of Precast Reduced Beam Section Connection

To prevent brittle damage and improve the post-earthquake rapid repair capability of beam–column connections, a precast reduced beam section (PRBS) connection joint that can be rapidly repaired under earthquake action was proposed in this study. Four specimens, including a repaired specimen, were subjected to a quasi-static test to investigate the seismic performance and repair ability of the connection. Seismic performance indices such as the failure mode, hysteresis curve, skeleton curve, strain distribution, and ductility were obtained through observations and analyses. The results indicated that the novel connection exhibited superior load-bearing, energy dissipation, and rotation capacities, compared to the welded flange-bolted web and traditional bone-weakened connections. This novel connection effectively relocated the plastic hinge to alter the failure mode and prevent brittle damage. Additionally, rapid post-earthquake repair was achieved by replacing the dog-bone-style splice section, maintaining a high load-bearing capacity and seismic performance. Finite element (FE) models were established to analyze the mechanical behavior of the specimens, and a parametric analysis was conducted to study the influence of different parameters on the load-bearing capacity of the connection. Based on the experimental and FE analysis results, the possible yield and failure modes of the connection were analyzed, and a calculation method for the bearing capacity of the PRBS connection was proposed. A comparative result demonstrates that the proposed calculation method can accurately predict the load-carrying capacity of a connection.

Cyclic performance welded steel reduced beam section moment connections using longitudinal slots in flanges

A new type of steel reduced beam section connection using longitudinal slots in the beam flanges is introduced. The effect of different parameters has been studied by the non-linear three-dimensional finite element method. Parameters have been the distance between the slot and column face, the length and width of the slot, the distance between the slot and the edge of the beam flange, the number of slots, the distance between slots, and the dimensions of the beam. The displacement controlled cyclic loading protocol recommended by SAC has been imposed. The von Mises yield criterion has been used. Obtained results show that creating the slots in the beam flange improves considerably the performance of the connection. The bending moment at the column face and plastic strains in the weld decrease by 32% and 94%, respectively, by increasing the slot length by 264%. The bending moment and dissipated energy reduce by 59% and 66%, respectively, when the slot width is increased by 430%. By increasing the length and width of the slot from a specific value and by moving the slot towards the beam web, the behaviour of the connection becomes unsatisfactory. The effect of the beam height is more than that of other dimensions of the beam. Based on the results obtained, recommendations for the design implications related to the geometric dimensions of the slots have been formulated.

Study on Collapse Optimization of Weak Axis Moment Connections

Abstract: 3D Weak axis moment connections are the connections between the beam with the web of an I section. But these connections are weaker as they are connected to the web which are thinner portions of the I section compared to flanges. This can lead to buckling of flanges. A new reduced beam section (RBS) connection, consisting of radius cuts in the beam flanges and circular openings in the beam webs, is proposed to allow for more ductile connections. RBS connections may increase structural deflection and crack width in the steel frame structure under large deformations. Therefore, it is extremely important to consider the bearing capacity and progressive collapse resistance of steel frame structures with RBS connections. Progressive collapse analysis of weak axis moment connections without any improvisation is taken for analysis and their collapse location and collapse resistance studied. To enhance weak joint connection design and to delay collapse time, we introduce reduced beam sections. Curved cell reduced beam sections are modeled and analysis is performed for various thickness of cell and by changing diameter. Thus, an effective size was obtained by combining the results with the conventional and the effective location of weak axis is improved

Seismic performance of the RBS connection with trapezoidal corrugated web (TCW-RBS)

This paper presents an evaluation of the performance of the trapezoidal corrugated web (TCW) reduced beam section (RBS) connection under cyclic loading. A series of experiments were conducted on three TCW-RBS specimens. The tests were carried out up to a 10% story drift ratio, and it was observed that the connection met the code-based limitations for a reduction in strength until reaching an 8% drift, surpassing the existing criterion for qualified connections in special moment frames. Additionally, nonlinear finite element analysis was utilized to investigate the influence of web angles on the behavior of TCW-RBS connections. The findings revealed that increasing the web angle resulted in a decrease in the maximum moment by up to 11%, while simultaneously enhancing the connection's ductility by up to 37%. Furthermore, the axial strain results in the web of the beam indicated that the corrugated web had a negligible impact on the flexural behavior of the connection due to the accordion effect. Notably, the maximum strain values in the flanges near the column face were three times lower than those in the reduced section zone, contributing to a reduced sensitivity of the welds to potential fractures.

Performance recovery of locally buckled reduced beam section connections by attaching buckling-restrained components

Reduced beam section (RBS) connections are ductile connections that have been widely used in steel structures. Because of the reduction of web resistance, local buckling usually occurs under large deformations and is associated with decreased strength. In addition, the complex deformation of beams prevents determining the residual strength, hence posing a challenge in postearthquake repairs. In this study, a buckling-restrained system (BRS) including steel channels and a mortar was proposed for deformed RBS regions to provide lateral support on buckled plates so as to recover the connection strength. Two full-scale RBS connections with various cutting ratios were first tested, and then the connection was repaired with BRS loaded again. The test results indicated that the repaired connections were loaded at a drift angle of up to 4% without fracture or strength deterioration. The negative strength increased by approximately 18%, and the maximum strength was similar to that of the original connection, indicating that the column-to-beam flexural strength ratio of the connection did not change. The strain at the heat-affected area also did not increase and rather decreased because of the additional support of the restraint. The dissipated energy capacities of the repaired specimens were approximately 92% and 87% of the values of the original specimens. These results confirmed that BRS provided sufficient lateral resistance and helped recover the connection performance.

Seismic performance of the enlarged beam section connection

AbstractEnlarged beam section (EBS) connection is a new moment connection developed to eliminate the shortcomings of conventional reduced beam section connections and fulfill desired performance. In EBS, the width of the flanges increases in specific locations between the desired plastic hinge and the column face of the beam to let the plastic hinge occur in a favorable region. Hence, the plastic hinge location can be controlled by manipulation of EBS parameters. In this study, the seismic performance of EBS connections under cyclic loading in the standard frameworks is investigated using finite‐element modeling. Before implementation the finite‐element model is verified by an experimental study on conventional connection. Utilizing optimum EBS parameters in the finite‐element modeling, no significant damage is predicted in weld lines and their vicinity, the column, and the connection zone. Also, no remarkable deformation or buckling instability is detected in the results. This indicates appropriate performance of the connection and formation of the plastic hinge in the desirable region. The requirements of various regulatory standards are achieved in terms on number of cycles and the total rotation. In addition, due to the ease of implementation, this connection type can be an excellent alternative to other moment connection types.

Inelastic cyclic response of RBS connections with jumbo sections

This paper examines the cyclic performance of reduced beam section (RBS) moment connections incorporating larger member sizes than those allowed in the current seismic provisions for prequalified steel connections, through experimentally validated three-dimensional nonlinear numerical assessments. Validations of the adopted nonlinear finite element procedures are carried out against experimental results from two test series, including four full-scale RBS connections comprising large structural members, outside the prequalification limits. After gaining confidence in the ability of the numerical models to predict closely the full inelastic response and failure modes, parametric investigations are undertaken. Particular attention is given to assessing the influence of the RBS-to-column capacity ratio as well as the RBS geometry and location on the overall response. The numerical results and test observations provide a detailed insight into the structural behavior, including strength, ductility, and failure modes of large RBS connections. It is shown that connections which consider sections beyond the code limits, by up to two times the weight or beam depth limits, developed a stable inelastic response characterized by beam flexural yielding and inelastic local buckling. However, connections with very large beam sections, up to three-times the typically prescribed limits, exhibited significant hardening resulting in severe demands at the welds, hence increasing susceptibility to weld fracture and propagation through the column. The findings from this study point to the need, in jumbo sections with thick flanges, for a deeper RBS cut than currently specified in design, to about 66% of the total beam width. This modification would be required to promote a response governed by extensive yielding at the RBS while reducing the excessive strain demands at the beam-to-column welds. Moreover, for connections incorporating relatively deep columns, it is shown that more stringent design requirements need to be followed, combined with appropriate bracing outside the RBS, to avoid out-of-plane rotation.

Numerical validation on novel replaceable reduced beam section connections for moment-resisting frames

This study presents replaceable reduced beam sections with connection detail for MRFs under residual drift. The proposed detail includes end-plated mid-spliced reduced beam sections. Pursuant to this goal, the proposed detail has been investigated under cyclic loading protocol required by AISC 341-16 by using ABAQUS finite element program. Seismic response of the proposed connection detail was compared from PEEQ and Rupture Index standpoint. The obtained findings indicate that the proposed mid-spliced replaceable reduced beam section satisfies all requirements indicated by AISC 341-16.

Numerical Investigation to Assess the Cyclic Performance of RBS Connection using Cover Plates

This paper presents the result of four welded connections under cyclic loading using finite element analysis, those are: Conventional Connection (C-Con), Cover Plates Connection (CP-Con), Reduced Beam Section Connection (RBS-Con), and RBS Connection using Cover Plates (RBSCP-Con) using the same material properties, including dimension of the profile and its span. Previous research indicates that, even though the fact that the initial seismic yield must be located far from the column’s face, it still occurs on the majority of RBS connections on occasion. By adding a cover plate to the top and bottom flanges of the beam, the research can provide a seismic design improvement for RBS connections. The analysis results observed that cyclic performance of RBSCP-Con was much superior to the other connections in terms of plastic hinges location, panel zone’s performance, and failure modes. However, CP-con has the maximum value of energy dissipation, which correlates with its hysteresis curves. Furthermore, all of the four types of connections already satisfy SMF category requirements in accordance with AISC 341-16.

A Parametric Study on Improved Reduced Beam Section Connections with Post-tensioning to Enhance Seismic Resilience

A Parametric Study on Improved Reduced Beam Section Connections with Post-tensioning to Enhance Seismic Resilience

Proposing two new methods to decrease lateral-torsional buckling in reduced beam section connections

Proposing two new methods to decrease lateral-torsional buckling in reduced beam section connections

Analytical Evaluation of RBS Moment Connection for Indian Profiles Under Seismic Behavior

The effects of Northridge (1994) and Kobe (1995) earthquake, intensive analysis and testing efforts are currently being sought for higher ways of designing seismic resistant steel connections. A connection with RBS (Reduced beam Section) is an acceptable solution to emphasizing a moment connection and can be the most reliable type of connection. Considering the benefits of RBS connection and the lack of information on resources in Indian standards, an analytical study of RBS connections of Indian profiles is performed. This study elaborates on Indian profiles to understand the beam-column connection’s overall performance characteristics during the cyclic response. FEA study is carried out to focus on improving the plastic deformation potential of the connection. The moment capacity of the connection is strengthened by the inclusion of RBS region in the beam. The seven specimens which includes Specimen without RBS, Flange cut RBS and Flange hole RBS have been designed and evaluated using the Finite element ABAQUS program. The findings of this study revealed that specimen without RBS exhibits low Seismic activity efficiency. While RBS specimens performed well, in all instances, Flange holes’ specimens demonstrate good performance.

Seismic performance of precast tubular web reduced beam section connection

A novel precast tubular web reduced beam section (PTWRBS) connection was proposed in this paper. The structure consists of a steel beam and a concrete-filled steel tubular column, which are spliced together by a prefabricated tubular web splice section, enable realize the function of post-earthquake resilience. To study the seismic performance of the PTWRBS connection, the commonly used bolted-welded (BASE) connection and PTWRBS connection were subjected to quasi-static tests to compare and analyze their performance in terms of failure modes, hysteresis curves, strain distribution, bearing capacity, ductility, and energy dissipation. After which, the second test was then conducted by replacing only the prefabricated tubular web splice section after the PTWRBS connection test. The results showed that the PTWRBS connection had a higher ductility and energy dissipation capability, with a terminal amplitude of up to 7% compared with the conventional connection. Moreover, the plastic hinge in PTWRBS connection was concentrated in the tubular web splice section. The repaired PTWRBS (REPTWRBS) connection still had a high bearing capacity and ductility. The PTWRBS and REPTWRBS connection both manifested good seismic performance in accordance with the seismic code. Additionally, finite element (FE) analysis software was used to numerically analyze the specimens, and the numerical analysis results were compared with the experimental results to verify the accuracy of the FE model and reveal the failure mechanism of the PTWRBS connection.

A novel principle for improving collapse resistance of steel frame structures

Although the reduced beam section (RBS) connection is an excellent seismic design for transferring plastic hinge, it is prone to fracture under the condition of large deformation. In addition to good seismic response, the performance of RBS connections needs to be improved to ensure good anti-progressive collapse response. In this study, a novel principle is proposed, in which the RBS connection is used to meet the plastic hinge transmission, and kinked reinforced bars are installed in the beam–column connection to realize a second path. Experimental and numerical investigations were conducted on a frame substructure with kinked reinforced bars, considering their diameter d, kinked height a and length l of the reinforced bars. The deformation capacity, vertical force vs. deformation response, failure mode, and contributions of the flexural and catenary actions on the reinforced bars were evaluated. The test results demonstrate that the kinked reinforced bars started to work when the reduced-beam-section connection with reinforced bars (RRBS) is in a plastic state. When the reinforced bars with a > 1.5d were installed at the beam end, the bearing capacity of the RRBS specimens increased with an increase in the diameter d and decreased with an increase in the length l of the reinforced bars. In addition, When the cracking first occurred at the reduced section, the bearing capacity decreased with an increase in the kinked height a. It is suggested to select the kinked height of the reinforced bar according to the deformation capacity of the beam.

Investigation on behavior and seismic performance of reduced beam sections

Engineers prefer reduced beam section (RBS) connections in steel moment frames built in earthquake zones due to their many benefits. The RBS shape design significantly affects joint behavior. This paper examines the effect of RBS geometry on joint behavior and seismic performance using ANSYS finite element analysis software. RBS connections are investigated using European profiles and steel grades due to the limited number of studies using European profiles in the literature. The simulation study is carried out in three stages. In the first stage, an experimental study in the literature is simulated, and the reliability of the created finite element model is checked. In the second stage, geometric changes are made to the verified numerical model, and the obtained new models are examined under monotonic loading to observe the effect of RBS geometry on moment-rotation behavior. In the third stage, the effect of the change in the RBS geometry on the seismic performance is investigated under cyclic loading. As a result of the study, the effects of various changes made in the RBS geometry on the joint behavior and seismic performance are presented graphically. By using the results of the analysis under monotonic loading, the regression analysis is carried out, and the formulas giving the elastic-plastic stiffness, elastic moment capacity, and elastic rotation angle of the support are derived. Besides, simulation models show that the RBS joints' seismic performance met the minimum criteria specified in the earthquake code (AISC/ANSI 341-16) when European steel profiles and quality are applied.

Thermal Effects on the Bearing and Ductility of Tubular Reduced Beam Section Connection: Numerical Investigation

In the present paper, an innovative fire-earthquake resistant joint called high-performance tube (HP-T) connection is presented and numerically validated. This HP-T connection improves the axial and rotational ductility as well as prevents brittle failure. Two series of models were simulated in ABAQUS software. In the first set of models, which was designed for heat simulation, a sequentially coupled thermal-stress analysis was performed to investigate the effects of different parameters such as web and flange tube thickness and the ratio of the applied load. To simulate the fire damage, two probable scenarios were considered: bottom flange tube damage and beam web damage when exposed to combined initial loading and fire. In the second set of models for seismic simulation, the failure mode, hysteretic curves, and strain distribution were analyzed. According to the results, HP-T robust connection not only provides appropriate ductility enhancement in force-variable fire conditions but also withstands at least 8% inter-story drift without considerable strength reduction.

Cyclic behavior of coupled steel plate shear walls with different beam-to-column connections

In a coupled steel plate shear wall system, the interaction between two steel plate shear wall piers provided by the coupling beams improves the overturning capacity of the structure. Quasi-static cyclic tests were conducted on three 1/3 scaled specimens to investigate the inelastic behavior with several different features. Each specimen had a different coupling beam-to-column connection, namely, a welded moment connection, a bidirectional bolted connection, and a cantilever endplate connection. The hysteretic behavior, envelope curves, ductility, and strength and stiffness degradation of the specimens were studied. The experimental results demonstrate that the introduction of concrete-filled square steel tubes is effective in resisting the demands imposed by the web plates and that the coupled steel plate shear wall system has the characteristics to provide good seismic performance. The specimen that had welded moment connections suffered weld fracture of the coupling beam-to-column connections while the coupling beams of the two other specimens had ductile shear yielding followed by tearing and fracture of webs. The strength and stiffness degradation of three specimens were similar and stable. Finite element models were developed to simulate the nonlinear behavior of the specimen that had welded moment connections and to study the benefits of employing modified connections with wing plate and reduced-beam section configurations. The modeling showed that wing plate and reduced-beam section connection could reduce demands at the critical welds and delay weld fracture. The connection type was found to have little influence on the internal force of the columns or the overall system behavior.