Exterior Reinforced Concrete Beam-Column Joints Research Articles

Seismic behaviour of Exterior RC beam-column joints repaired and strengthened using post-tensioned metal straps

Exterior beam-column joints are the most vulnerable part of substandard reinforced concrete (RC) buildings and are often the first to be damaged during earthquakes. This article presents an experimental and numerical investigation into the behaviour of exterior RC beam-column joints repaired and strengthened using Post-Tensioned Metal Straps (PTMS) for active confinement. The study focused on full-scale beam-column joints with an inadequate core zone detailing, thus emulating the deficiencies found in existing substandard RC buildings. Initially, four “bare” joints were subjected to cyclic tests to induce substantial damage within the core zone. Subsequently, the damaged core of the joints was repaired and recast with new concrete, and PTMS were applied to strengthen the joints, followed by another round of cyclic testing. The experimental findings were compared with predictions generated through established models from existing literature. The results revealed that ASCE/SEI 41–17 guidelines accurately predict the shear capacity of the bare joints. It is shown that recasting the core with new concrete significantly increased the joint’s shear capacity by up to 42% compared their bare counterparts. The use of PTMS strengthening further enhanced the capacity by up to 25%. A “scissors model” was employed for numerical simulations of both bare and PTMS-strengthened joints using DRAIN-2DX, which proved effective at predicting their nonlinear load-displacement envelope response. This article contributes towards the development of new cost-effective post-earthquake strengthening techniques for beam-column joints, with the potential to reduce the vulnerability of substandard RC buildings in developing countries.

Probabilistic Shear Strength Model of Reinforced Concrete Exterior Beam-Column Joints

Probabilistic Shear Strength Model of Reinforced Concrete Exterior Beam-Column Joints

Numerical Analysis of Reinforced Concrete Exterior Beam-Column Joints Under Limited Cycles of Repeated Loading

The beam-column joints play an important role in the structures where the functions of connection shortage by transport the forces like shear, moment, and torsion from the beam to the column. So, this study represents an attempt to investigate the performance and the effect of limited cycles of repeated load on the strength of the exterior beam-column joint core. Therefore, 34 specimens have been investigated by using a numerical analysis that used the finite element method. To simulate these specimens, the concrete damage plasticity model was used to define the concrete materials and the nonlinear isotropic/kinematic (combined) hardening model for steel material definition. These models are involved in the ABAQUS software package, version 2020. This study involves key parametric studies on beam-column joints, which are summarized as changing the ratio of shear reinforcement of the joint core in addition to using two types of shear reinforcement. This study also includes the effect of flexural reinforcement of the beam as well as the beam’s shear reinforcement effect on the strength of the beam-column joint. To calibrate the software to simulate a realistic result, three specimens have been used, which have been tested in previous studies. It has been found that this numerical model accurately predicts the experimental response under limited cycles of repeated loading. The ultimate load from modelling was compared with the experiment once, having a difference of less than 10% and the ultimate displacement having a difference of less than 11%. It has been found that increasing the ratio of the joint’s shear reinforcement to double has no significant effect on the ultimate load. Otherwise, decreasing it to half leads to a decrease in the ultimate load compared with a specimen that is designed according to ASCE352-02R. This study has studied the effectiveness of increasing the shear reinforcement by adding an x-shape reinforcement. Also, the flexural reinforcement of the beam has found it has increased the ultimate load capacity by 48% Where the ratio of flexural reinforcement increased to 1.8%, the load bearing capacity was enhanced.

Seismic performance of the shear-deficient exterior RC beam-column joints strengthened with PHSW

This paper presents a study on the seismic performance of shear-deficient exterior reinforced concrete (RC) beam-column joints strengthened with prestressed high-strength steel wire (PHSW). This strengthening technique overcomes the space obstacle of the orthogonal beams and the shortcomings of traditional seismic strengthening techniques for the beam-column joints. To verify the feasibility and effectiveness of the proposed strengthening technique, six large-scale exterior beam-column joints were tested under reversed cyclic loading. The seismic performance of strengthened joint specimens was analysed and compared with that of the original un-strengthened and the code-compliant specimens to investigate the effects of the ratio of PHSW and the prestressing level of wires. The failure mode of the exterior joints had been changed from brittle joint shear mode to ductile beam flexural mode after being properly strengthened, and the load-bearing capacity of the joint specimen can be improved by up to 20%. Other seismic performance parameters of reinforced specimens, such as ductility and energy dissipation capability, were also significantly enhanced with increased PHSW ratio and prestress level. The strengthening scheme is easy to implement, and no anchorage failure occurred during the loading process, indicating that the strengthening technique is feasible, effective, and economical. Based on the test results and theoretical analysis, a formula for calculating the load-bearing capacity of the exterior RC beam-column joint strengthened with PHSW was developed to predict the load-bearing capacity of the strengthened exterior RC beam-column joints.

Experimental and Numerical Investigation on Seismic Performance of RC Exterior Beam-Column Joints with Slabs

The effect of a cast-in-place slab on the beam-column joint at beam ends in reinforced concrete (RC) structures under earthquake attacks has not been fully understood, and therefore, it is not manifestly addressed to some of the design criteria or specifications. Consequently, the contribution of slab to the seismic resistance of structures is often ignored or just included in an approximate manner. In this study, the experiment of two 1/2-scaled exterior beam-column joints without slabs and three 1/2-scaled joints with slabs under the combination of quasi-static repeated cyclic loading and constant axial force was carried out to investigate the effect of the cast-in-place slab on the seismic performance of exterior beam-column joints. The results show that for specimens EBCJ1 and EBCJ2 without slab, the decline was approximately 5%, while for specimens EBCSJ1 and EBCSJ3, the decline in the load is obvious and approximately more than 10%. For specimen EBCSJ2, which exhibited a slightly different behavior in the hysteresis curves, the maximum carrying capacity reached at the displacement of 70 mm during the first cycle. The cast-in-place slab has different effects on the failure mechanism and load transfer mechanism of the exterior beam-column joint, which depends on the column-beam moment strength ratio in the loading protocol. The slab has a positive effect on the energy dissipation capacity of the joint but has a negative effect on the load carrying capacity. In addition, finite element (FE) analysis of the tested specimens was conducted. The FE numerical models were established based on the construction information and loading conditions from the experiment and then validated by comparing them with the experimental observation.

Numerical Analysis Exterior RC Beam-Column Joints with CFRP Bars as Beam’s Tensional Reinforcement under Cyclic Reversal Deformations

In this paper the cyclic lateral response of reinforced concrete (RC) beam-column joints with composite carbon fiber-reinforced polymer (CFRP) bars as a longitudinal reinforcement in the beam is simulated with finite element (FE) modeling using software Abaqus. An experimental project of two full-scale joint specimens subjected to cyclic loading with supplementary accompanying pull-out tests of CFRP bars is also included in this study. These test results are used to calibrate the developed FE model, the constitutive laws of the materials and the bond response between CFRP bars and concrete. Comparisons between test data and numerical results indicate that the calibrated model accurately predicts the cyclic response of RC beam-column joint specimens with CFRP longitudinal bars as the beam’s tensional reinforcement. A parametric analysis is also performed to provide useful concluding remarks concerning the design of concrete joints with composite bars and the ability of CFRP bars to substitute for conventional steel bars in RC structural members under seismic excitations.

Experimental response of unreinforced exterior RC joints strengthened with prestressed steel strips

The response of unreinforced beam-column joints represents a key issue in seismic vulnerability and fragility assessment of existing Reinforced Concrete (RC) buildings. A great attention has been focused on the investigation of the experimental response of unreinforced joints and their possible strengthening strategies.In this study, an experimental investigation of the response of exterior RC beam-column joints strengthened with prestressed steel strips is presented. Four full-scale specimens were tested, two non-strengthened and two strengthened. The non-strengthened specimens were built with (specimen S) or without (NS) stirrups in the joint panel and were tested for reference and comparison purposes, in order to reproduce a seismic code-compliant and a non-conforming RC joint, respectively. The strengthened specimens had two different layouts characterized by a higher (CAM1) or lower (CAM2) complexity of installation and level of building disruption.The response of specimen NS was controlled by joint panel failure following beam yielding, whereas the specimen S showed a ductile response, controlled by beam flexural failure. The response of specimens CAM1 and CAM2 demonstrated the effectiveness of the adopted technology. For CAM1, a ductile response was observed, similar to specimen S. For CAM2, a joint panel failure following beam yielding was observed, as for specimen NS, but with a significantly higher global ductility.The presence of prestressed steel strips led to a delay in the onset of diagonal cracking, with a slight increase in strength at this condition, i.e. by 8%, but a significantly higher deformation capacity, with the drift increasing, on average, by 122%. The strengthening led to a relatively slight increase in the resistance of the subassemblage, which was very similar in specimens S, CAM1 and CAM2, and, on average, 11% higher than in specimen NS. Instead, a much more significant difference was observed in terms of deformation capacity, with the drift at conventional ultimate condition in specimens CAM1 and CAM2 77% and 61% higher than specimen NS, respectively.The experimental results are reported, and the effectiveness of the tested strengthening solutions is discussed, in terms of global response of the subassemblage, observed damage evolution, energy dissipation capacity, and local response, such as joint shear distortion and measured strain of strengthening steel strips.

Evaluation of structural performance for beam-column joints with high-strength materials under cyclic loading using PIV technique

Current design codes require long bar development length and high joint hoop ratio in reinforced concrete (RC) exterior beam-column joints using high-strength materials, which reduces constructability. This study investigated the seismic behavior of RC exterior beam-column joints with insufficient joint hoops and using high-strength beam flexural bars (Grade 600 MPa) and/or high-strength concrete. Six half-scale exterior beam-column joints were tested under cyclic load reversals. The test parameters included the yield strength and diameter of beam flexural bars and the concrete strength. As an innovative measurement method, particle image velocimetry (PIV) technique was implemented to accurately measure the joint shear deformation, beam flexural deformation, plastic hinge length, surface strain fields, and crack patterns in the beam-column joint specimens. The PIV method predicted the location of beam cracks accurately. The test results showed that the use of high-strength bars increased bond-slip due to higher bond requirement, which decreased the energy dissipation capacity by 16% compared to the joint specimen using Grade 400 MPa bars. Further, the joint shear deformation and the beam crack width increased, while the plastic hinge length decreased. The combined use of high-strength concrete and high-strength bars improved the structural performance in terms of the energy dissipation capacity and initial stiffness.

A Nonlinear Macro-Model for the Analysis of Monotonic and Cyclic Behaviour of Exterior RC Beam-Column Joints

The study presents a numerical investigation on exterior reinforced concrete (RC) beam-column joints under seismic actions based on a macro-modelling approach proposed by the authors in a recent paper. The followed approach makes use of the well-known “scissors model” where two nonlinear rotational springs arranged in series were introduced to schematize the shear behavior of the joint panel and, moreover, the possible occurrence of the debonding of longitudinal steel rebars at the beam-joint interface. In this paper, the scissor model is employed in the context of a novel predictive approach with the twofold objective to: 1) develop a new model for the estimate of the maximum shear strength of RC joints by performing a multivariate linear regression analysis on a set of experimental tests and, 2) define a new multilinear backbone joint shear stress-strain law to be assigned to one of the mentioned springs. In particular, the identification of the shear strain parameters is obtained by performing a sensitivity analysis in which a number of monotonic load-drift numerical curves are derived by varying the strain values in ranges opportunely a-priori defined and compared with the experimental ones to investigate their accuracy. Finally, cyclic analyses on RC joints collected in the experimental database are carried out by considering the backbone joint shear stress-strain law identified in the calibration process. The analyses are performed by using the nonlinear open-source finite element platform, OpenSees, in which the “pinching4” uniaxial material model, available in the software library, is implemented to set the parameters governing the hysteresis rules and pinching effect. To this purpose, five literature proposals suggesting the values to use for such parameters are taken into account and their assessment is presented in the paper. The obtained outcomes have allowed, on the one hand, to identify the proposal providing the best numerical simulations of the experimental results and, on the other end, to draw useful indications on how to further improve the cyclic modelling by opportunely modifying the setting of the “pinching4” material model parameters.

Composite steel beam is commonly used element in multistory steel buildings today. The composite action between the concrete deck and the steel beam reduces both steel weight and deflection, accordingly, enhance floor economy and serviceability. Many earlier researches were carried out to optimize the design of the composite steel beams under both static loading and dynamic behavior. None of these

In many situations, it is necessary to have a beam web opening in the plastic hinge location. However, very limited studies investigated the behavior of reinforced concrete (RC) beam-column joints with nearby beam web openings. A previous study was conducted for investigating the behavior of beam-column joints with unreinforced nearby web opening. In this study, the effect of adding additional reinforcing around a nearby web opening on the seismic behavior of RC exterior Beam-Column joints is being investigated. Nine full-scale beam-column joints were tested, four joints had an unreinforced opening, while five joints had reinforced opening. The behavior of the beam-column joints is described in terms of maximum resisting load, deflection, energy dissipated, and stiffness degradation. The behavior was significantly affected by the nearby opening. The increase in opening width and the reduction in the distance between the opening and the column resulted in decreasing the strength and ductility of the RC beam-column joint. However, adding additional reinforcement improved the behavior. Thus, it is recommended to provide additional reinforcement all around the opening.

In many situations, it is necessary to have a beam web opening in the plastic hinge location. However, very limited studies investigated the behavior of reinforced concrete (RC) beam-column joints with nearby beam web openings. A previous study was conducted for investigating the behavior of beam-column joints with unreinforced nearby web opening. In this study, the effect of adding additional

the paper presents an efficient scheme for a Nonlinear PID (NPID) controller to improve the dynamic response of the Electric Vehicle (EV). The objective of the proposed controller is to track accurately the reference speed selected by the driver of the EV. A MATLAB/Simulink model is established and validated for the considered EV to study the system performance. The proposed NPID controller has been investigated by comparing it with the traditional PID controller. The optimal parameters of Both the NPID and PID controllers were obtained using the Harmony Search (HS) optimization technique based on a cost function. The desired rise time, settling time, steady-state error, and overshoot have been taken into account in the cost function. Two tests were performed, the first test was implemented at fixed reference speed while the second one was carried out at a staircase command of reference speed. The simulation results can be summarized as follows: in the first test, the NPID controller reaches the steady-state speed at 38.12 seconds while the PID controller stabilizes at 44.68 seconds. Moreover, the NPID controller has a 0.5% steady-state error however, the PID controller has a 4% steady-state error. Besides, the second test shows that the NPID controller can decrease the root mean square of error by 30.1% compared to the PID controller. Lastly, the proposed NPID controller can enhance EV performance significantly.

Quasi-static cyclic performance of RC exterior beam-column joint assemblages strengthened with geosynthetic materials

The beam-column joints are the most critical and vulnerable part of the RC framed structures when subjected to earthquake load. The objective of the present study is to investigate the cyclic behaviour of seismic and non-seismic exterior reinforced concrete (RC) beam-column joints strengthened with innovative polymeric based geosynthetic materials. Two variants of geosynthetic material named geogrid and geotextile were used for strengthening the beam-column joints in the experimental program. In this strengthening protocol, two different types of strengthening patterns were used in which one was horizontal U-shaped pattern, and the other one was the diagonal cross (X-shaped) pattern. All the beam-column specimens were tested under the quasi-static cyclic loading with controlled amplitude to explore the cyclic performance on the parameters such as failure modes, hysteresis loops, load-deformation envelope curves, ductility, energy dissipation capacity, stiffness and strength degradation behaviour, pinching width ratio, damage index and joint distortion. The test results showed that the adopted strengthening schemes with geotextile and geogrid materials could successfully alter the failure of beam-column joints from shear to flexural and improved the ductile behaviour of the strengthened specimens. The load-carrying capacity and ductility-factor of the geosynthetic strengthened specimens significantly increased up to 48.4% and 37.8%, respectively when compared to the non-seismic control specimen, and it was highest in geogrid strengthened BCJs, especially in diagonal X-shape bonded specimen. The significant increment of energy dissipation capacity was also observed as 2.08 to 3.73 times for the strengthened specimens. Furthermore, the post-elastic performance and the joint shear strength of strengthened RC beam-column joints was also improved in comparison to the non-seismic control specimen. In addition, an analytical study was carried out to predict the shear strength contributions of externally bonded strengthening materials in the RC beam-column joint, which was compared with experimental findings. A good agreement was observed between the analytical and experimental results. Hence, the experimental and analytical study of the strengthened beam-column joints using geotextile and geogrid have confirmed that the appropriate bonding of these materials to the concrete can improve the seismic performance of the non-seismic exterior RC beam-column joints.

Improved shear strength model for exterior reinforced concrete beam-column joints using gene expression programming

Beam-column joints without transverse reinforcement can be considered as a weak link in reinforced concrete (RC) moment-resisting framed structural systems, particularly when subjected to seismic lateral loads. It is essential to fully understand the shear behavior of RC beam-column joints to avoid significant damage and eventual failure of RC structures in the case of joint panels excessively damaged. This study aims at developing a framework for systematic understanding of the shear behavior of RC beam-column joints where a novel joint shear strength model is presented. Totally, 56 test results on exterior RC beam-column joints without transverse reinforcement from various sources were used. The proposed model was generated by the utilization of the gene expression programming (GEP) approach. Thus, statistically, significant tests were applied for evaluating the different parameters influencing the shear strength of the joint, e.g., material features, design variables, and joint geometrical and detailing configurations. The proposed model was able to appropriately reflect the contribution of each variable of the beam-column joints involved in the GEP. The presented findings also include a comparison of the developed GEP-model with the existing analytical models, i.e., the conjectures of these available models were compared with the achieved results of this study. It is demonstrated that the presented GEP-model more accurately predicted the shear strength of RC beam-column joints than the existing models, having a much smaller coefficient of variation of 0.093 for the ratio between the predicted and experimentally determined shear strength values, compared to other models available in the literature.

Seismic behavior of exterior RC beam-column joints without code-specified ties in the joint core

Beam-column joint design for reinforced concrete (RC) buildings is a critical issue for modern earthquake engineering, because for these structural elements, the current codes provide several geometrical constraints and reinforcement provisions, which may be very complex to implement during the construction phase. To investigate how a construction error might influence the joint behavior, two identical full-scale exterior beam-column joints specimens are built, according to Italian Building Code specifications for the high ductility class, but without the required horizontal ties inside the joint panel. This construction error could be plausible because, according to the design drawings, the panel was very crowded with reinforcement bars and the concrete casting and compaction was objectively difficult. The performance of the joints is tested under cyclic loads simulating seismic actions. Although the joints are designed for high ductility class, a 50% reduction of the horizontal reinforcement in the joint core, and 25% in the critical regions, led the specimens to shear failure, with crushing of the concrete in the joint core. A discussion of the failure mechanism is presented, in which shear strength obtained from the tests is compared to shear strengths calculated using the expressions provided for exterior joints by Eurocode 8, the ACI Code and the formula proposed by Pauletta et al.

Repair of severely-damaged RC exterior beam-column joints with FRP and FRCM composites

This paper presents the results of an experimental program aimed at comparing the cyclic behavior of three full-scale reinforced concrete (RC) exterior beam-column joints repaired with externally bonded composites. Preliminary, the specimens suffered significant damage, which resulted in a beam-joint (B + J) failure, i.e. shear failure of the panel joint after yielding of longitudinal reinforcement in the beam. The damaged specimens were then repaired using either Fiber Reinforced Polymer (FRP) or Fiber Reinforced Cementitious Matrix (FRCM) composites, and the same loading history was applied to the repaired specimens. The experimental behavior was compared with that of original specimens, and results are presented in terms of load-carrying capacity, stiffness deterioration, ductility, dissipated energy, and equivalent damping viscous ratio. Results allow to clearly identify the contribution of the externally-bonded composites to the overall behavior of the repaired specimens.

Experimental Behavior and Design of Exterior Reinforced Concrete Beam-Column Joints Strengthened with Embedded Bars

AbstractShear-deficient RC beam-column joints (BCJs) represent one of the main factors behind the seismic damage suffered by existing concrete infrastructure, as well as the associated loss of life...

A practical model for simulating nonlinear behaviour of FRP strengthened RC beam-column joints

Generally, beam-column joints are taken into account as rigid in assessment of seismic performance of reinforced concrete (RC) structures. Experimental and numerical studies have proved that ignoring nonlinearities in the joint core might crucially affect seismic performance of RC structures. On the other hand, to improve seismic behaviour of such structures, several strengthening techniques of beam–column joints have been studied and adopted in practical applications. Among these strengthening techniques, the application of FRP materials has extensively increased, especially in case of exterior RC beam-column joints. In current paper, to simulate the inelastic response in the core of RC beam–column joints strengthened by FRP sheets, a practical joint model has been proposed so that the effect of FRP sheets on characteristics of an RC joint were considered in principal tensile stress-joint rotation relations. To determine these relations, a combination of experimental results and a mechanically-based model has been developed. To verify the proposed model, it was applied to experimental specimens available in the literature. Results revealed that the model could predict inelastic response of as-built and FRP strengthened joints with reasonable precision. The simple analytic procedure and the use of experimentally computed parameters would make the model sufficiently suitable for practical applications.

Experimental Study on Structural Performance of RC Exterior Beam-Column Joints Retrofitted by Steel Jacketing and Haunch Element under Cyclic Loading Simulating Earthquake Excitation

Several retrofitting methods for reinforced concrete (RC) beam-column joints in old buildings without seismic details were developed. Four half-scale RC exterior beam-column joints were fabricated and tested under cyclic loading simulating earthquake excitation. The control specimen was designed to fail in joint shear. Two practical retrofitting strategies were applied to the control specimen which consider the architectural characteristic in real buildings, including steel jacketing and haunch retrofit solution. The structural performance of the test specimens was investigated in terms of various factors including damage and failure, load-drift relationship, ductility, dissipated energy, and strain profiles of longitudinal reinforcement. Experimental results confirmed that the proposed retrofit methods were shown to enhance the seismic capacity of the joints in terms of the strength, deformation capacity, and energy dissipation capacity while the shear deformation in the panel zone significantly reduced in comparison with the control specimen.

Study on exterior RC beam-column joints upgrade with SIFCON in joint core under reversed cyclic loading

Beam-column joint is a key component of a Reinforced Concrete (RC) moment resisting frame and should be designed and detailed properly, particularly when the frame is subjected to earthquake seismic forces. Failure of beam-column joints is governed by bond and shear failure mechanism which are brittle in nature. Therefore, all international codes insist sufficient anchorage to longitudinal bars and confinement of core concrete in resisting shear. In this paper, the behavior of exterior RC beam-column joints with Slurry Infiltrated Fibrous Concrete (SIFCON) in the joint core under reversed cyclic loading is presented. Beam-column joints made entirely with RC, Fibre Reinforced Concrete (FRC) and SIFCON are also investigated for comparison. A total number of ten specimens corresponding to five test series are cast and tested under reversed cyclic loading to study the load deformation behavior, ductility associated parameters, ultimate load carrying capacity and failure characteristics. A nonlinear finite element model is also developed using FEA software ANSYS to validate the experimental results such as load-deflection response and the corresponding failure modes. From the test results, it is observed that the ultimate load carrying capacity, stiffness, ductility and energy dissipation capacity are improved to a greater extent for beam-column joints with SIFCON when compared with that of conventional RC beamcolumn joints.

Improved strut-and-tie method for 2D RC beam-column joints under monotonic loading

In the previous analytical studies on 2D reinforced concrete (RC) beam-column joints, the modified compression field theory (MCFT) and the strut-and-tie method (STM) are usually employed. In this paper, the limitations of these analytical models for RC joint applications are reviewed. Essentially for predictions of RC joint shear behaviour, the MCFT is not applicable, while the STM can only predict the ultimate shear strength. To eliminate these limitations, an improved STM is derived and applied to some commonly encountered 2D joints, viz., interior and exterior joints, subjected to monotonic loading. Compared with the other STMs, the most attracting novelty of the proposed improved STM is that all critical stages of the shear stress-strain relationships for RC joints can be predicted, which cover the stages characterized by concrete cracking, transverse reinforcement yielding and concrete strut crushing. For validation and demonstration of superiority, the shear stress-strain relationships of interior and exterior RC beam-column joints from published experimental studies are employed and compared with the predictions by the proposed improved STM and other widely-used analytical models, such as the MCFT and STM.