Exterior Beam-column Connections Research Articles

Efficacy of Hybrid Fibre Reinforced ECC in RC Exterior Beam-Column Connections

Efficacy of Hybrid Fibre Reinforced ECC in RC Exterior Beam-Column Connections

Post-tensioned steel beam-column connections with reduced length BFRP tendons

The seismic behavior of the traditional top and seat angle beam-column connection was experimentally evaluated using a half-scaled prefabricated exterior beam-column connection subassembly. Then, an ensemble of three post-tensioned beam-column connections using reduced length basalt fiber reinforced polymer (BFRP) tendons was tested with three different tendons' post-tension (PT) force levels of 15.9, 30, and 50% of the tendons' ultimate strength. Following that, another group of three additional subassemblies containing both reduced length BFRP tendons, as post-tensioning devices, and top and seat angles, as energy dissipation (ED) devices, was tested with the same three post-tension force levels used in the previously tested group. Finally, an analytical model was proposed to capture the moment-relative rotation response of the traditional top and seat angle and the connection combining both the top and seat angles and the BFRP tendons. The results showed that connections containing BFRP tendons only, with the lowest PT force level, provided the same envelope of the top and seat angle connection, and further enhancement could be achieved by increasing the PT force level. Also, the addition of the BFRP tendons to top and seat angle connection improved the connection strength, initial stiffness, post-yield stiffness, and reduced the residual drift. In addition, the proposed analytical model predicted the moment-relative response well, which ensures the reliability of the model in designing such connections.

Seismic Behavior of Monolithic Exterior Beam-Column Connections with Unbonded Post-Tensioning

Seismic Behavior of Monolithic Exterior Beam-Column Connections with Unbonded Post-Tensioning

Nonlinear analysis of interior and exterior beam-column connections under reversed cyclic loading

This paper presents a case study into the application of nonlinear finite element for the analysis of interior and exterior beam-column joints under reversed cyclic loading. Three beam-column joints, with different reinforcement configurations and test conditions, were considered to assess the accuracy of the currently available constitutive models in predicting the full hysteretic response of beam-column joints under reversed cyclic loading. To this end, the three beam-column joints were modelled in ATENA-GiD which implements nonlinear constitutive models for steel and concrete, the latter of which are formulated within the context of crack-band and crush-band approaches. In this paper, the default constitutive models in the program were employed to evaluate the accuracy of the existing modelling and analysis procedures. From the series of results presented, it is shown that the existing constitutive models are capable of predicting various aspects of the joint behaviour under reversed cyclic loading with good accuracy. This includes the peak load capacity, degrees of pinching and strength degradation, strength and stiffness degradation, unloading and reloading stiffnesses, crack patterns and failure modes.

Nonlinear finite element investigations on different configurations of exterior beam-column connections with different concrete strengths in column and floor

The fast development of quality concrete production has increased the usage of high-strength concrete (HSC) in the columns of high-rise buildings where high axial column loads exist. In contrast, normal-strength concrete (NSC) is used in the floor system for economic reasons. This produces a weak concrete zone at the intersection of columns and floors. Studies focused on evaluating the performance of such connections are still limited. The current numerical study investigates the performance of such connections. The developed numerical model has been verified against the experimental test for connections with different column-to-beam strengths. The numerical model has demonstrated acceptable accuracy compared to the experimental results. Moreover, the validated model has been employed to investigate the influence of different column-to-floor strengths on connections with and without transverse beams and floor slabs. It has been found that the strength and stiffness of connections with different concrete strengths have been improved compared to monolithic connections. Furthermore, the increase in joint strength and stiffness for connections with different column-to-floor strengths is more pronounced for connections with transverse beams and floor slabs due to their contribution to achieving proper confinement conditions for the weak concrete in the joint zone. In addition, the presence of a transverse beam affects the induced stress of the beam bars, resulting in a change in the mode of failure to beam flexural failure, whereas the presence of a slab floor increases both the stiffness and flexural strength of the beam. However, connections with the floor slab suffered high damage due to the transferred equilibrium torsion. Moreover, connections with different column-to-floor strengths exhibited larger stains in their joint stirrups; hence, additional joint stirrups are recommended to avoid the brittle shear failure of the joint. The study ended by evaluating the response of such connections under high axial column loads. It has been observed that planer connections perform poorly in terms of strength and ductility, while adequate performance has been observed for connections with transverse beams or slabs. Therefore, the role of the transverse beam and slab should be taken into account in the design of the connections with different column-to-floor strengths.

Structural behavior of shear deficient high performance reinforced concrete exterior joints under bending

Structural performance of shear deficient reinforced concrete exterior beam-column connections made with Engineered Cementitious Composite (ECC) and Ultra-high Performance Concrete (UHPC) is investigated experimentally and compared with those made of Self-Consolidating Concrete (SCC). Beam-column connections of 1/3rd scale made entirely of ECC, SCC and UHPC as well as ECC-SCC and UHPC-SCC combinations (joint core zone made of ECC and UHPC while the rest made with SCC) are tested under monotonic flexural loading to failure. The performance is compared in terms of failure mode, ductility, energy absorption capacity, stiffness, load/moment-displacement/rotation response, stress–strain characteristics, crack patterns/widths, member flexural/shear strength and joint shear strength. SCC and SCC-UHPC joint specimens have non-ductile beam shear failure and shear failure of the SCC part of the connection respectively, while all others have joint flexural failure. Code based equations significantly under predicted the shear strength of ECC and UHPC joint members. All connections made fully or partially with UHPC and ECC have exhibited higher ductility (1.2 to 1.7 times), energy absorption capacity (3.1 to 15.7 times) and reserve joint strength compared to those with SCC. UHPC incorporated connections exhibited higher strength and energy absorbing capacity, those with ECC showed higher ductility and better crack control characteristics and incorporation of ECC/UHPC can induce desired flexure dominated failure in a shear deficient joint.

Effect of connection transverse reinforcement on the behavior of GFRP-RC T-connections: Numerical investigation

This study numerically investigates the cyclic behavior of glass fiber-reinforced polymer (GFRP) reinforced concrete exterior beam-column (T-BC) connections (GFRP-RC T-BC connections) with varying amounts of transverse reinforcement (TR) in the connection panel. The amount of TR required to provide adequate confinement and shear strength to the GFRP-RC T-BC connections has not yet been fully understood. The primary objective of this study was to evaluate the effects of TR configuration and amount of TR on the load-drift ratio response, strain distributions and shear strength of the GFRP-RC T-BC connections. The numerical investigation was conducted using the numerical models developed in ATENA software and validated against the test results of four T-BC connections (one steel-RC and three GFRP-RC). The TR ratio and TR configurations (2 leg, 3 leg, and 4 leg horizontal stirrups) in the connection panel were the main parameters of the numerical study. Results of the numerical study indicated that increasing the TR ratio in the connection panel to 0.72% significantly enhanced the peak load, stiffness and drift ratio capacity of the GFRP-RC T-BC connection. Four leg TR configuration showed significantly better performance of the GFRP-RC T-BC connections due to the higher confinement factor than the other TR configurations. A shear strength equation was proposed for the GFRP-RC T-BC connections, which represents a linear relationship between shear strength and the TR ratio up to 0.60%, followed by stable shear strength of 0.85fc′ for a TR ratio up to 1.30%.

Performance of exterior beam-column connections with innovative bar anchorage schemes: Numerical investigation

Proper detailing of the joint reinforcement is essential for achieving an optimum framing action of the connected members. The ACI 352R-02, ACI 318–19 and EC-8 codes specify minimum requirements for the components of the standard 90-degrees hook; horizontal part, bend, and vertical tail as a reliable detailing alternative for achieving satisfactory performance of the joint. This numerical study aims to investigate the optimum tail length needed for ensuring adequate performance of the exterior joint and to develop a measure for the joint shear strength under various vertical tail length conditions, utilizing two experimentally tested joints with different reinforcement details as reference. The impact of a wide range of vertical tail lengths on the joint’s ultimate strength has been evaluated. It has been found that the provided tail length governs the joint's ultimate shear strength, where providing a vertical tail length of thirty times the bar diameter or greater achieves the superior performance, which is attributed to the improved confinement to the joint and the better bond condition in the joint region. However, the available column depth determines how the vertical tail length affects the joint strength, where the influence is more significant for joints with narrow depth columns. Thus, this study reveals that the dependence on increased vertical tail length, as a non-conventional alternative, can be safely considered to ensure sufficient joint shear strength, especially in joints with narrow depth columns. Hence, the limits of tail length given by several international codes; e.g., ACI 352R-02, ACI 318–19, and EC-8, are inadequate. Furthermore, an accurate equation for predicting the joint shear strength has been developed based on an extensive parametric study on various sets of exterior joints, taking into account the tail length under various conditions of column depths, joint aspect ratio, column axial stress, and the concrete strength.

Cyclic Performance of GFRP-RC T-Connections with Different Anchorage and Connection Details

This study investigated the effects of different configurations of connection reinforcement and anchorages on the cyclic behavior of glass fiber–reinforced polymer (GFRP) reinforced-concrete (RC) exterior beam–column connections (T-connections). Three full-scale GFRP-RC T-connections were tested under reversed cyclic loading. One connection was detailed with 90-degree hooked anchorage and horizontal stirrups, while the other two connections were detailed with L-shaped anchorage by placing additional Z- or U-shaped bars at the connection region. The objective of this study was to investigate the influence of the anchorage type (90-degree hook or L-shaped) at the end of the longitudinal bars of the beam on the cyclic performance (strength, ductility, and energy dissipation) of GFRP-RC T-connections. Moreover, the anchorage performances in terms of anchorage resistance, bond stress–slip of bars within the joint were evaluated and compared with each other. Test results indicated that all the connections passed a 5.09% drift ratio without any loss of strength. The addition of U-bars into the L-shaped anchorage connection significantly improved the strength, ductility, and energy dissipation compared with the other two connections.

Numerical investigation of RC exterior beam-column connection with different joint reinforcement detailing

The proper detailing of joint reinforcement plays an essential role in ensuring adequate performance of reinforced concrete frames in terms of strength and ductility. The influence of various options of joint reinforcement detailing on joint performance has been numerically investigated using the nonlinear finite element analysis software, ABAQUS. Two sets of beam-column connections of various joint reinforcement detailing with greater spacing between the stirrups at two different locations have been modeled for achieving this purpose, considering validated experimentally tested specimen as reference. This study reveals that achieving the minimum requirments of joint reinforcement ratio according to the ACI 318-19 and ACI 352R-02 codes utilizing both internal cross ties and outer stirrups with greater spacing between the stirrups rather than closely spaced outside stirrups only is more efficient in terms of joint strength and deformation capacity. This implies that the contribution of the inner cross ties considering their configuration and location in the shear strength resistance should be considered. Therefore, the joint stirrups' main role should be considered as tension ties and a crack-control reinforcement that requires less steel and wider spacing for the joint details rather than the confinement of the concrete. Furthermore, it has been observed that both the joint strength and deformation capacity have been significantly improved with the use of three layers of stirrups with two closed rectangular cross ties or one polygon cross tie. However, the employment of only two layers of stirrups with two crossed rectangular cross ties located at the middle third of the joint as well as diagonal bars at the corners between the beam and column of the joint core successfully controlled the joint cracks and improved the performance of the connection.

Cyclic Behavior of High-Strength Lightweight Concrete Exterior Beam-Column Connections Reinforced with GFRP

Using lightweight reinforced concrete beams with glass fiber bars (GFRP) is one approach for achieving the requirement seismic design idea of “strong-columns weak-beams”. Twelve full-scale normal-strength concrete (NC with fc` = 32 MPa) and high-strength lightweight concrete (HSLWC with fc` = 42, 49 and 52 MPa) exterior beam-column joints have been tested under cyclic loadings. The beams were reinforced with conventional steel bars (CS) and GFRP using steel fibers (SF). The experimental joint shear force was compared with that estimated by some international codes such as the American Concrete Institute (ACI-19), the Egyptian code (ECP-07), and the New Zealand Code (NZS-06). Nonlinear finite element analysis (ABAQUS) was carried out. In the present study, three main parameters were explored (1) HSLWC, (2) GFRP ratios equal to 0.70%, 1.03% and 1.37%, (3) SF ratios equal to 0.0%, 0.75% and 1.50%. The findings of the experiment revealed that increasing the concrete strength from NC with conventional steel bars to high-strength lightweight concrete HSLWC (fc` = 42 MPa) with the same ratio of GFRP bars enhanced the first cracking load by about 25%. Increasing the SF ratio to 1.50% enhanced the failure load by 18–24% when compared with non-fiber specimens. The predicted joint shear strength estimated using the equations of the ACI 318-19 and ECP-07 are conservative for HSLWC exterior beam-column connection reinforced with GFRP bars but the predicted joint shear strength by using the equations of the NZS-07 is on the borderline for some cases. The finite element program ABAQUS can be used successfully to forecast the behavior of HSLWC beam-column connections reinforced with GFRP under seismic loadings.

Cyclic performance of exterior R.C beam-column strengthened with different thicknesses of CFRP sheets

The recent ground motion results indicated that the RC buildings are required to be retrofitted by different strengthening techniques. Nowadays, the external strengthening gain interest since its easy, cost effective and not required redesign of buildings. The CFRP sheets are suitable solution and utilized by a number of researchers. However, the numerical cyclic performance of connection strengthened with different thicknesses of CFRP need to be well investigated. This study assessed the performance of RC exterior beam column connection strengthened with CFRP sheets First, two grades of concrete are utilized to be control specimens, normal concrete compressive strength (C20) and high concrete compressive strength (C50) then, the specimens are retrofitted with different thicknesses (1.2, 2.4, 3.6mm) of CFRP sheets. The stresses and damage states showed the importance of connection retrofitting. The CFRP shift the plastic hinge zone away from the panel zone. Furthermore, the results demonstrated that by increase of CFRP thickness the connection resistance will be improved. The comparison between the hysteresis curves demonstrated that the yield and ultimate loading were enhanced for strengthened connection for both concrete grades and the incremental in thicknesses also increase them. The outputs also exhibited that the stiffness and ductility has increased for retrofitted specimens indicating that the CFRP comprehensively overcome the applied cyclic loading and the beam column connection is able to resist such type of loading.

Evaluation of critical connections in an irregular precast building

This study aims at analyzing and designing the precast columns and beams in an irregular precast building. This building is designed as a moment-resisting framed structure with infill walls for Seismic and Wind loading using the Finite element software ETABS. Based on the structural analysis results one critical interior beam-column connection and one critical exterior beam-column connection are identified and an emulative connection is proposed. The element sizes and the reinforcement detailing of these critical columns and beams are presented. An emulative column-beam junction detail is proposed to achieve a moment-resisting action. This connection is simple and similar to a cast-in-place connection and doesn’t require sophisticated methods of connection such as prestressing, welding etc. The structural response of the building in terms of story displacement, story shear, story stiffness, story drift, time period and modal mass participation are also discussed. The use of advanced materials like micro concrete, engineered cementitious composites, Ultra high-performance concrete, and high strength steel rebar for in-situ concreting in the beam-column junction has advantages like reduced congestion, and reduction in cracking of concrete under severe seismic loading conditions.

Seismic performance of welded flange plate (WFP) connections in composite steel structures

This paper studies the seismic behavior of welded flange plate (WFP) connections of steel beams to H-shaped columns with composite floors. Nonlinear finite element models of exterior beam-column connections under monotonic and quasi-static cyclic loadings are developed in ABAQUS commercial software. Geometric, material, and contact nonlinearities are considered in the models, and the specimens are loaded up to the final failure point. The von-Mises J2-plasticity model with bilinear kinematic hardening and ductile damage parameter is employed to simulate steel constitutive behavior, and reinforced concrete is modeled by the Concrete Damage Plasticity (CDP) model enhanced with embedded steel rebars. Load-carrying capacity, ductility, failure modes, strain distribution, and energy dissipation capacity of the specimens are compared, and various effects of composite action are studied. The research represents the importance of considering the composite action in the design process, which contrasts with the common practice. Based on these observations, a novel reduced beam section detailing is proposed, which circumvents the issues with current design configurations, and provides an optimal seismic behavior for WFP composite connections.

Nonlinear Numerical Assessment of Exterior Beam-Column Connections with Low-Strength Concrete

The ductility and capacity of reinforced concrete beam-column connections depend mainly on the concrete’s strength and the provided reinforcements. This study investigates numerically the role of low-strength concrete in beam-column joints utilizing ABAQUS software. In this simulation, a newly developed stress-inelastic strain relationship for both confined and unconfined low-strength concrete is used. This study recommended a specific value of the concrete dilation angle for both substandard and standard joints. Also, stirrups’ yield strength value was found to play an insignificant role in improving the shear resistance of such joints with low-strength. In addition, the joint shear strength prediction using empirical models that implicitly consider the stirrups contribution in improving joint resistance was found to be better than the prediction of other models that explicitly consider the stirrups’ presence. The numerical results also showed that the use of a diagonal steel haunch as a joint retrofitting technique significantly increases the joint shear capacity and changes its brittle shear failure into a ductile beam flexural failure.

Full-scale experimental testing of RC beam-column joints strengthened using CFRP ropes as external reinforcement

Common reasons often impose the strengthening of elements of existing reinforced concrete structures designed according to various regulations including contemporary codes. Such reasons could be the change of the initial purpose of the structure, the need to increase the seismic capacity due to alteration of the seismic characterization of the region, the adding of an extra story on the top of the structure or just the need for increasing the seismic capacity of the structure. Τhe innovative material of carbon fiber ropes is used as externally applied reinforcement for the strengthening of reinforced concrete exterior beam-column connections and the efficiency of this technique is experimentally investigated. Eight full-scale exterior connection subassemblages are constructed and tested under increasing imposed cyclic deformations. Six of the specimens are strengthened by applying external X-shaped ropes at each side of the body of the joint and straight ropes at each side of the beam while two control specimens are tested without being strengthened. All ropes are placed into notches curved on the concrete surface. The hysteretic responses of the tested specimens are presented and compared to one another. Further, a damage index is calculated and used to evaluate the efficiency of the applied strengthening technique. The strengthened joints exhibited improved hysteretic response compared to the unstrengthened specimens in terms of maximum loads per loading step, stiffness, energy dissipation and damage index and it is deduced that the application of the carbon fiber ropes as external strengthening reinforcement has been proved to be an efficient strengthening technique.

Numerical modeling the effect of an opening on the behavior of exterior beam-column connections under cyclic loading

For the operation of buildings, using beam web openings near the beam-column connection could be essential. In this current study, the effect of a web opening on the performance of reinforced concrete (RC) exterior Beam-Column connections (BCCs) is being investigated. Ten full-scale BCCs were tested under cyclic loading. A numerical model was developed, which was validated using experimental results. A parametric study was conducted using the numerical model in order to investigate the influence of opening geometry and details in terms of reinforcement around, reinforcement of in the joint core, opening proximity to support, and opening aspect ratio on the performance. The performance of the BCCs was described in terms of maximum resisting load and stiffness degradation. While the failure load of the BCC is significantly reduced the closer the opening to the column and the wider the rectangular opening. Such effects are pronounced in the opening without reinforcement compared to those with additional reinforcements around the opening. Thus, it is essential to take these effects in design provisions.

Seismic retrofit of exterior beam-column joints using steel angles connected by PT bars

A review of past earthquakes has shown that due to the lack of specific seismic details for beam-column joints, the brittle mechanisms of the structure caused by the joint behavior often lead to severe damage or even collapse of the building. Fracture of the beam-column connection is common in these mechanisms due to shear failure of connection core or reinforcement slip. The aim of this paper is to seismically retrofit the external beam-column connections without specific seismic details in existing reinforced concrete structures, considering the effect of the slab and transverse beam. For this purpose, the beam-column connections have been retrofitted using prestressed angles and bars based on the enlargement of the beam-column connection core. In this regard, seven half scale exterior beam-column connections were subjected to lateral cyclic loading with increasing amplitude. The tested specimens consist of four control specimens, one of which has special seismic details and the other three control specimens do not have special seismic details and have shortcomings such as lack of cross-sectional reinforcement of the connection core, increase of intervals for cross-sectional reinforcement of beams and columns and lack of sufficient anchorage length (with no end hook) for bottom longitudinal beam reinforcements below the beam in the connection core. The other three retrofitted specimens, like the control specimens, do not have the seismic details. Experimental results show that the use of this retrofit system has shifted the plastic hinges to the outside of the joint core and improved the bond between the concrete and the longitudinal tensile reinforcement in the joints. Moreover, the retrofit method increases loading capacity, energy dissipation, damping percentage, stiffness and ductility capacity of the members.

A Review-Behavior of Reinforced Concrete Exterior Beam-Column Connections under Cyclic Loading

In many seismically active regions worldwide, massive reinforced concrete (RC) structures built before the 1970s existed. These older RC buildings, in countries having seismic history, were designed for gravity loads only. Anyway, the beam-column connections influence the structures where the functions of connection shortage by transport the forces like shear, moment, and torsion through the beam to the column. Also, it could behave in a ductile manner to help the structure resist the seismic, as simulate the seismic loading by high and low cyclic loading. Due to the failure of external joints more than the internal beam-column joints, this review focuses on the behavior of exterior beam-column joints under cyclic loading, consequently simulated the behavior under an earthquake and the reinforcement detailed.

Finite Element Analysis of Key Influence Parameters in Reinforced Concrete Exterior Beam Column Connection subjected to Lateral Loading

Beam column connection is the most critical zone in a reinforced concrete frame. The strength of connection affects the overall behavior and performance of RC framed structures subjected to lateral load and axial loads. The study of critical parameters that affects the overall joint performances and response of the structure is important. Recent developments in computer technology have made possible the use of Finite element method for 3D modeling and analysis of reinforced concrete structures. Nonlinear finite element analysis of reinforced concrete exterior beam column connection subjected to lateral loading was performed in order to investigate joint shear failure mode in terms of joint shear capacity, deformations and cracking pattern using ABAQUS software. A 3D solid shape model using 3D stress hexahedral element type (C3D8R) was implemented to simulate concrete behavior. Wire shape model with truss shape elements (T3D2) was used to simulate reinforcement’s behavior. The concrete and reinforcement bars were coupled using the embedded modeling technique. In order to define nonlinear behavior of concrete material, the concrete damage plasticity (CDP) was applied to the numerical model as a distributed plasticity over the whole geometry. The study was to investigate the most influential parameters affecting joint shear failure due to column axial load, beam longitudinal reinforcement ratio, joint panel geometry and concrete compressive strength. The Finite Element Model (FEM) was verified against experimental test of exterior RC beam column connection subjected to lateral loading. The model showed good comparison with test results in terms of load-displacement relation, cracking pattern and joint shear failure modes. The FEA clarified that the main influential parameter for predicting joint shear failure was concrete compressive strength.