Beam-column Joint Specimens Research Articles

Seismic Retrofitting of Nonseismically Detailed Exterior Reinforced Concrete Beam-Column Joint by Active Confinement Using Shape Memory Alloy Wires

It is widely accepted that the seismic retrofitting of nonseismically detailed reinforced concrete beam-column joints (BCJs) in reinforced concrete (RC) frame buildings is an urgent necessity due to its high vulnerability and potential consequences in seismic events. As a result, considerable effort has already been put into developing efficient and practical retrofitting solutions for such BCJs. Most of the existing techniques, however, are based on either passive confinement techniques, for example, fiber reinforced polymer (FRP) wrappings, or involve a considerable joint enlargement, which, in many cases, is undesirable. In this study a new technique of retrofitting BCJs is proposed by employing a more effective method of confinement (i.e., active confinement), utilizing the shape recovery feature of shape memory alloys (SMAs). To evaluate the performance of the proposed retrofitting scheme, experimental tests were conducted on full-scale BCJ specimens. The efficacy of the proposed retrofitting scheme is evaluated in terms of enhancement in strength, ductility, energy dissipation capacity, damage reduction in the specimens, and ease of application. The results from this study suggest that the proposed retrofitting scheme could be effectively used in achieving the full capacity of the joints corresponding to beam yielding and consequently enhances the energy dissipation capacity of the system significantly. The test results demonstrated that the proposed retrofitting scheme performs excellently in reducing the joint shear strain (core damage) (to almost zero or negligible) and also in retaining the full axial load carrying capacity of the column, even at very large drift values. The proposed retrofitted scheme could also be conveniently used in cases where the capacity ratio of column-to-beam needs to be improved.

Failure Behavior of CFRP-Strengthened Reinforced Concrete Beam–Column Joints under Reversed-Cyclic Lateral Loading: Mechanical and Acoustic Emission Observations

This paper investigates the failure behavior of reinforced concrete beam - column joints (BCJs) strengthened with different schemes of carbon fiber reinforced polymer (CFRP) and the factors causing fracture. In the study, five reinforced concrete BCJ specimens having 1/1 geometric scale were tested under reversed-cyclic lateral loading. While one of them was used as a reference, the others were strengthened with CFRP. Damage development of the specimens was simultaneously monitored by the acoustic emission (AE) technique. Both the structural and AE data were combined to reveal the effects of CFRP strengthening schemes on the fracture pattern ana damage progress. Quantities, scales, levels, and locations of the damage show that the scale of the damage decreased with all strengthening procedures and that the strength and other mechanical properties improved. In addition, extending the strengthening material to the columns and beams contributed more to the structural behavior in terms of strength, energy dissipation capacity and rigidity as well as crack development. Although strengthening by wrapping only the beam and column extensions of the joint can give the desired performance in terms of load bearing capacity, it is not recommended owing to an increased risk of major shear cracks.

Seismic behavior of reinforced concrete beam-column joints with unstressed steel strands fully or partially used for beam longitudinal reinforcement

Five beam-column joint specimens: three exterior and two interior specimens were subjected to cyclic loading to investigate the effectiveness of using unstressed Grade 1860 MPa steel strands as full/partial replacement for the conventional Grade 420 MPa deformed bars as beam longitudinal reinforcement. The study also developed a special hooked anchorage detail to anchor the steel strands in the joint region. The test specimens failed by beam plastic hinge formation near the column face as intended in design, with drift capacities between 5.12% and 7.57%. However, the full (100%) and partial (50%) replacement of deformed bars by strands led to a 58% and 28% decrease in average relative energy dissipation. Despite this, the full/partial replacement of deformed bars by strands as beam longitudinal reinforcement resulted in enhanced reentering capabilities. Fracture of longitudinal steel strands observed in the beam plastic hinge region at the end of the test indicated the effectiveness of the special hooked anchorage detail in allowing steel strands to develop their capacity. Further, the flexural strength of the beams of test specimens was evaluated through a detailed moment-curvature analysis, which predicted the beam flexural strength with high accuracy and less variation (mean = 1.01, standard deviation = 0.02). After that, beam flexural strengths were evaluated following the ACI 318–19 procedure modified to include the proposed bilinear strand model, which produced conservative estimates of beam flexural strength (mean = 1.15) suitable for design. Also, the procedure to estimate the beam's probable flexural strength is presented. Finally, required modifications to the conventional seismic design procedure were proposed to incorporate the use of strands as beam longitudinal reinforcement.

Hysteresis Performance and Restoring-Force Model of Precast Concrete Ring-Lap Beam-Column Joints

In order to study the restoring-force characteristics of precast concrete ring-lap beam-column joints, three precast concrete ring-lap beam-column joint specimens and one cast-in-place concrete beam-column joint specimen were designed and fabricated, and low-circumferential repeated loading tests were conducted. The results show that the bearing capacity of the ring-lap beam-column joint is higher than that of the cast-in-place beam-column joint, and with the increase in the lap length, the bearing capacity, ductility, and energy dissipation capacity of the ring-lap beam-column joint increase significantly, and the local damage is also mitigated. Based on the test results and the existing restoring-force model theory, a trifold restoring-force model is proposed for precast concrete ring-lap beam-column joints considering the effect of lap length. The proposed restoring-force model is consistent with the hysteresis curve of the assembled column, which indicates that the proposed restoring-force model can better reflect the influence of the lap length on the hysteresis characteristics, and can provide a reference for the structural elastic–plastic analysis and engineering application of the precast concrete ring-lap beam-column joint. The proposed restoring-force model can better reflect the influence of lap length on the hysteretic properties, which can provide a reference for the structural elastoplastic analysis and engineering application of this precast concrete ring-lap beam-column joint.

Confined ultrahigh-performance fibre-reinforced concrete in retrofitted beam–column joint: experimental study

The beam–column joint (BCJ) is a critical region in a framed structure because during such events as earthquakes it is susceptible to earlier failure than adjacent members, leading to shear failure, and will endanger building users if not designed properly. BCJs designed using preseismic code provisions follow the non-ductile approach and might not resist postelastic rotation without enduring greater damage. Retrofitting techniques offer great opportunities for strengthening damaged BCJs. In this study, the effectiveness of a novel retrofitting scheme based on carbon fibre reinforced polymer (CFRP) confined ultrahigh-performance fibre-reinforced concrete (UHPFRC) in rehabilitating initially damaged BCJ specimens was assessed. Three retrofitting schemes using UHPFRC with and without confinement are proposed: (1) in situ casting of 25 mm thick UHPFRC jackets; (2) in situ casting of steel wire mesh-confined UHPFRC and (3) in situ casting of CFRP-confined UHPFRC. The confining action was achieved by sandwiching wire or CFRP mesh between two layers of UHPFRC. The results of this study indicate that BCJ specimens retrofitted with confined UHPFRC had improved overall seismic response, compared with specimens retrofitted only with UHPFRC. Further, the wire mesh-based retrofitting scheme proved to be more efficient than the CFRP mesh-based scheme.

Experimental Analysis of the Effectiveness of Pre-Stressed Steel Strips for the Strengthening of Beam-Column Joints in Existing RC Buildings

Beam-column joints in existing Reinforced Concrete (RC) buildings are usually characterized by the absence of transverse reinforcement. The observation of post-earthquake damage, as well as several numerical and experimental studies, have soundly demonstrated the possible impact of the response of unreinforced joints on the damage – up to collapse – of existing RC buildings under seismic action. In this study, a possible strengthening approach for these elements, based on CAM® technology, is investigated through experimental tests. The results of these tests are reported, along with the results of a previous experimental campaign carried out on the same topic. Full-scale external beam-column joint specimens are tested, with and without strengthening, and with different characteristics in terms of amount of beam longitudinal reinforcement and concrete compressive strength. Different failure modes are observed for the as-built specimens (joint failure without (J) or after (BJ) beam flexural yielding). The effectiveness of the adopted strengthening approach is demonstrated, observing an increase in joint shear strength and subassemblage ductility and – unless a joint failure in compression occurs – a possible modification of the failure mode into a ductile, flexure-controlled response of the subassemblage, as for code-compliant beam-column joints.

Seismic behavior of novel GFRP bar reinforced concrete beam-column joints internally reinforced with an FRP tube

Due to many advantages, fiber-reinforced polymer (FRP) bars have been considered as a promising alternative to steel bars in reinforced concrete (RC) structures. The use of FRP bars in beam-column joints has been reported in the literature. However, it has been found that the energy dissipation capacity of an FRP-RC beam-column joint is dramatically lower than that of the corresponding steel-RC joint. The present study attempts to develop a novel form of FRP-RC beam-column joints with superior energy dissipation capacity. The proposed joints incorporate an internal FRP tube in the joint zone, which provides confinement to the inner concrete and shear resistance of the joint. Compared with existing reinforcement techniques using stiffeners or internal diaphragms, the proposed use of an internal FRP tube is much easier to be implemented. To demonstrate the advantages of the proposed FRP-RC beam-column joints, an experimental program consisting of 6 FRP-RC beam-column joint specimens was carried out. The effects of fiber type, thickness, and fiber orientation of the FRP tube in the joint zone were investigated. The test results in terms of failure modes, hysteretic behaviors, and energy dissipation capacities of the test specimens were discussed in detail. The test results demonstrated the efficiency of the FRP tube, especially the one with a fiber angle of ±45°, in enhancing the energy dissipation capacity of FRP-RC beam-column joints.

Machine learning-based seismic damage assessment of non-ductile RC beam-column joints using visual damage indices of surface crack patterns

After a significant earthquake, the updated status of the structural elements is usually determined based on a qualitative visual inspection. Although visual inspection provides a prompt assessment of the damaged elements, the output of this subjective method is influenced by the experience and decision of a trained inspector, which may vary from case to case. In this study, an innovative machine learning-based procedure is developed to automate damage state identification of non-ductile reinforced concrete moment frames (RCMFs) utilizing visual indices of crack patterns of the concrete surface. An extensive database including 264 surface crack patterns is constructed corresponding to 61 non-ductile beam-column joint specimens tested under the quasi-static cyclic loads at different drift ratios. Two visual damage indices, including the cumulative length of cracking and the areal density of crushing, are extracted using image processing filtering on the collected images. Supplementary information of the specimen, such as aspect ratio and concrete compressive force, is also considered as input variables. Various machine learning-based predictive models are developed for estimating the maximum drift ratio of a damaged non-ductile beam-column joint based on the available information of the specimen. Two scenarios are considered based on the accessibility of the compressive strength of the concrete as the input data, and a predictive model is obtained for each scenario. The peak experienced drift ratio predicted by the proposed methodology is finally used as an engineering demand parameter attributed to the corresponding fragility curves to determine the damage state of non-ductile RCMFs.

Experimental and numerical investigations on square CFST column to U-shaped steel-concrete composite beam joints with internal T-shaped diaphragms

An innovative joint detail with internal T-shaped diaphragms for concrete-filled steel tubular (CFST) columns to U-shaped steel-concrete composite (USCC) beams is proposed in this study. Five beam-column joint specimens are tested under cyclic loading to evaluate the seismic performance. The test parameters are the connection form between top reinforcing bars (re-bars) and steel tubes, the total cross-section area of top re-bars, and the strengthening method for the joint. Test results show that welding the U-shaped steel directly to the steel tube may lead to premature fracture of bottom flanges in the connection vicinity; the H-steel corbel and the strengthening plate help delay the fracture of bottom flanges, and increase the joint's positive bending capacity effectively. The joint shows superior negative bending capacity, and the plastic stress distribution assumption can be utilized to calculate the joint's negative bending capacity with reasonable accuracy. While the joint shows lower positive bending capacity when premature fracture of bottom flanges occurs, thus the elastic stress distribution assumption is suggested for calculating the joint's positive bending capacity. Additionally, a finite element (FE) model is developed and verified. The effects of axial load ratio, the total cross-section area of top re-bars, the width to thickness ratio of steel tubes, and the thickness of the strengthening plate on the joint's bending capacity are investigated numerically. It is found that the joint's bending capacity decreases with the increase of axial load ratio and width to thickness ratio of steel tubes. The strengthening plates increase the positive bending capacity, and the top re-bars enhance the negative one.

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 study of U-shaped steel-concrete composite beam to square CFST column joints

Concrete-filled steel tubular (CFST) columns and U-shaped steel-concrete composite (USCC) beams have received extensive attention because of superior mechanical performance over steel and reinforced concrete members. In this study, an innovative cost-effective and construction-effective USCC beam to CFST column joint configuration with T-shaped internal diaphragms is proposed. Four beam-column joint specimens were designed according to the proposed design provisions, and were tested under combined constant axial compression and cyclic lateral loading, including one specimen with T-shaped diaphragms in strong direction, two specimens with T-shaped diaphragms in weak direction, and one control specimen with conventional internal diaphragms. Test results revealed that the specimens with T-shaped diaphragms exhibited similar cyclic behavior, moment-bearing capacity, ductility, stiffness, and energy dissipation capacity to the specimen with conventional internal diaphragms. The primary failure modes were fracture and buckling of bottom flange of the U-shaped steel in the connection vicinity, leading to a remarkable pinching effect in the cyclic behavior. All specimens were tested up to a story drift ratio of 4%, showing good elasto-plastic deformation capacity. The specimens have a superior bearing capacity under negative moment and a lower one under positive moment due to premature fracture of bottom flange. All specimens were classified as the semi-rigid and partial strength joint under positive moment, semi-rigid and full strength joint under negative moment. Additionally, the contributions to story drift were analyzed theoretically and the results via the proposed calculation formulas were found to be in good agreement with the measured story drift.

Experimental study on seismic performance of prefabricated viscoelastic damping bolted joints

Aiming at the defect of insufficient bearing capacity of prefabricated concrete beam-column joint with bolted connection, a prefabricated viscoelastic damping bolted joint (VDBJ) is proposed with good seismic performance. The damping principle is based on that viscoelastic (VE) dampers can provide energy dissipation and additional stiffness for the structures. Three full-scale beam-column joint specimens were designed, including one cast-in-place joint specimen, one prefabricated bolted joint specimen without VE dampers and one prefabricated bolted joint specimen with VE dampers. Since the viscoelastic damper is a passive energy dissipation device with velocity correlation, comparison and analysis of three specimens under high-frequency cyclic loading are performed on the failure modes and seismic performance indexes such as hysteretic energy dissipation, displacement ductility, stiffness degradation and ultimate bearing capacity. The analysis of the test results indicate that the proposed prefabricated viscoelastic damping bolted joint has stronger ultimate bearing capacity and displacement ductility than the cast-in-place joint. The arrangement of VE dampers effectively controls the appearance and expansion of concrete cracks, which not only achieves the expected effect of shock absorption and energy dissipation, but also can realizes the rapid replacement of components after the earthquakes.

Peak drift ratio estimation for RC moment frames using multifractal dimensions of surface crack patterns

In this paper, a novel computer-vision based methodology is developed for predicting the seismic peak drift ratio of damaged reinforced concrete moment frames using surface crack patterns. A comprehensive database comprising 974 surface crack images from cyclic test results of 256 beam-column joint specimens at various drift ratio levels is collected. The database covers a broad range of concrete compressive strengths, rebar and stirrup strengths, longitudinal and transverse reinforcement ratios, beam and column length to depth ratios, in-plane configurations, and failure modes. Multifractal dimensions of damaged beam-column subassembly images are obtained by the box-counting algorithm to capture the complexity and irregularity of the surface crack patterns. The variation of multifractal dimensions with the peak drift ratio is investigated for specimens with strong and weak joints. Empirical equations are developed that predict the peak drift ratio during an earthquake according to the corresponding crack patterns. Four scenarios are considered based on the availability of the structural properties as the input data, and for each scenario, a unique predictive equation is obtained. Finally, the application of the proposed methodology is described for an example specimen at various drift ratios. Interestingly, the multifractal dimensions of the crack pattern alone as the input data lead to an acceptable accuracy level for the peak drift ratio estimation. The peak drift ratio predicted by the proposed equations can finally be used to identify the damage state and performance level of the reinforced concrete moment frames in accordance with relevant specifications.

Experimental and numerical study on reinforced concrete beam-column joints with diagonal bars: Effects of bonding condition and diameter

Diagonal bars anchored in beams have been proven to be an effective reinforcement detail for reinforced concrete interior beam-column joints (BCJs) in mitigating the congestion of conventional stirrups without compromising their seismic performance. This paper investigates the effects of bonding condition and diameter of diagonal bars on the seismic performance of interior BCJs. Four interior BCJ specimens, including one control specimen reinforced with conventional stirrups and three others reinforced with diagonal bars, were fabricated and tested under cyclic loading. The results show that the control specimen fails with plastic hinges formed at the beam-joint interfaces, while all other specimens fail with relocated plastic hinges on the beams. The two BCJ specimens reinforced with bonded and debonded diagonal bars show similar improvement over the control specimen in terms of joint damage level, loading capacity, energy dissipation, stiffness degradation, and bonding condition of beam longitudinal reinforcement. For instance, the BCJ specimens reinforced with bonded and debonded diagonal bars possess 9% and 12% higher loading capacity, and 13% and 7% higher energy dissipation than the control specimen. Debonding the diagonal bars can slightly reduce joint cracks but has marginal effect on the overall performance of BCJs. In addition, the debonding treatment weakens the contribution of the diagonal bars to joint shear resistance, as evidenced by the increased strain in joint stirrups. Furthermore, increasing the diameter of debonded diagonal bars enhances the ductility and energy dissipation of the BCJ specimens since this improves their buckling resistance after concrete spalling. In addition, finite element models for BCJs were developed and validated for parametric study. The simulation results indicate that insufficient diagonal bars can lead to unsuccessful relocation of plastic hinges in BCJs, which decreases the loading capacity and accelerates the load degradation. With similar total sectional area, reducing the number of diagonal bars deteriorates their anchorage in beams. This consequently weakens the flexural capacity at beam ends, leading to unsuccessful plastic hinge relocation and poor seismic performance of BCJs.

Tensile and flexural behaviors of connections between steel beam and concrete-encased-and-filled steel tube column

Concrete-encased-and-filled steel tube (CEFT) columns with a circular tube section can be potentially used for hollow precast concrete (PC) constructions, in which thin PC encasement is used to reduce the lifting weight of a large PC column. In the present study, connection methods were studied for steel beam-CEFT column joints with the thin concrete encasement. Two sets of testing were performed focusing on the local behavior of the connection: 1) monotonic tension test for beam flange-column connections, and 2) cyclic loading test for beam-column joints. In the first test, the local out-of-plane behavior of the flange plate-tube connections and the associated damage mode of the concrete encasement were identified. The load-deformation relationships of the test specimens were evaluated by nonlinear finite element analysis. Based on the results, exterior beam-column joint specimens were designed, and the flexural behavior of the connections was verified under cyclic loading. The joint specimens were strengthened with connection methods such as tension bars, thick steel tube, and vertical continuity plate, inducing the beam failure. In particular, the thick tube and vertical continuity plate were effective in restraining the concrete damage. The tensile and flexural strengths of the test specimens were evaluated using design equations.

Experimental investigation of initially damaged beam column joint retrofitted with reinforced UHP-HFRC overlay

The present experimental study investigates the effectiveness of ultra-high-performance hybrid fiber reinforced concrete (UHP-HFRC) overlay for retrofitting the initially damaged reinforced concrete beam column joint (BCJ). Eight control BCJ specimens are tested under quasi static reverse cyclic loading. The ‘Park and Ang’ damage indices are calculated for four distinct damage states, i.e., complete, severe, moderate and slight from the load displacement curve of the control specimen. Each set of specimens were subjected to reverse cyclic loading to achieve their respective damage states. Each damaged specimen is then retrofitted using the wire mesh as reinforcement in the UHP-HFRC overlay. The retrofitted specimens using reinforced UHP-HFRC overlay exhibited the improvement in the load-carrying capacity, ductility, drift capacity, energy dissipation, equivalent viscosity damping, stiffness retention at higher drift, and lower strength degradation for a given damage level. However, the performance of the retrofitted BCJ specimens significantly depends upon the initial damage state of the BCJ. The improvement in the performance of the retrofitted specimen gradually decreases as the initial damage state of BCJ shifted from slight to complete; nevertheless, the performance of all the retrofitted samples is better than the controlled specimen.

A Study on Self‐Consolidate Concrete in Experimental Reinforced‐Concrete Beam Column Structures with Alccofine and Steel Fiber

This paper discusses the concept of self‐consolidating concrete mix with Alccofine‐1203, superplasticizer, viscosity modification agent, crimped steel fiber on the RC beam column joint. Totally, eight reinforced‐concrete (RC) column joints with M25 grade concrete were considered in this study. Out of eight RC beam column joints, two beam column joints served as Alccofine, two beam column joint specimens served as Alccofine 5%, two beam column joint specimens served as Alccofine‐10%, and two beam column joint specimens served as Alccofine‐15%. All the RC beam column joint specimens were tested under the compression until failure in the loading frame of 2000 kN capacity. The test results of Alccofine‐10% showed the higher loading capacity than that of Alccofine‐5% and Alccofine‐15% in self‐consolidating concrete RC beam column joints. The percentage of superplasticizer, viscosity modification agent, and crimped steel fiber is maintained. Nonlinear finite element analysis (FEA) to analyse the beam column joint through nonlinear finite element modelling (NLFEM) and the modelling results were compared from the experimental results. The results obtained through ANSYS modelling show good agreement with the experimented results. The deflection ductility of experimental results shows 1.57, and the predicted deflection ductility shows 1.59 in beam column joint with Alccofine‐10%. ANSYS software is validated as appropriate software to predict the study parameters of self‐consolidation concrete in beam column joints.

Relocating plastic hinges in reinforced concrete beam-column joints by mechanically anchored diagonal bars

The implementation of strong column-weak beam concept in reinforced concrete (RC) moment-resisting frames results in the formation of plastic hinges at the beam ends, which could lead to the strain penetration of beam longitudinal reinforcement into beam-column joint (BCJ) cores. This causes high shear forces inside joint cores, bonding deterioration of longitudinal reinforcement and consequently jeopardizes the seismic behaviour of BCJs. Plastic hinge relocation by mechanically anchored diagonal bars has been proposed to mitigate such potential damage to BCJ cores. This paper investigates the effect of relocating distance of plastic hinge on the seismic performance of BCJs with mechanically anchored diagonal bars. Five interior BCJ specimens including one control specimen reinforced with conventional stirrups and four others reinforced with mechanically anchored diagonal bars were tested under cyclic load. Test results indicate that the plastic hinges can be generally relocated by different distances to the anchorage ends of diagonal bars. Increasing the relocating distance can enhance the loading capacity and stiffness of BCJs, but also increase the potential of joint shear failure. The ductility, energy dissipation and joint shear deformation of BCJs are first improved then reduced as the relocating distance increases. Although the strain penetration of beam longitudinal reinforcement into the joint cores can be gradually alleviated as the plastic hinges are moved farther away from the joints, the induced bending moments at the beam ends are amplified and subsequently increase the joint shear forces. Moreover, increasing the length of anchorage segments increases the forces sustained by the mechanically anchored diagonal bars. Therefore, a lower bound of the relocating distance of plastic hinges is recommended to take advantage of the benefits from reduced strain penetration, while an upper limit needs to be specified to avoid joint shear failure. In addition, an analytical model is developed to predict the failure modes and loading capacities of BCJs with the plastic hinges relocated by different distances. A satisfactory agreement between the prediction and the experimental results is obtained.

Analytical Model for the Design of HSFC and UHSFC Jackets with Various Steel Fiber Volume Fraction Ratios for the Retrofitting of RC Beam-Column Joints

High-strength steel fiber-reinforced concrete (HSFC) and ultra-high strength steel fiber-reinforced concrete (UHSFC) jackets have been proved experimentally to be much more effective with respect to other strengthening schemes in improving the hysteresis performance of existing substandard reinforced concrete (RC) structural members. In this paper, an existing analytical model for the prediction of the shear capacity of RC beam-column joints strengthened with a HSFC or UHSFC jacket is extended to provide design formulation of these innovative HSFC and UHSFC jackets. An authoritative validation of the proposed formulation is also achieved by comparisons of experimental results of 50 beam-column joint specimens with the analytical predictions of the model. Test data used for verification have been collected from the literature based on experimental studies of the authors and other researchers. The merits of the HSFC and UHSFC jacketing technique are also highlighted in the state of practice. Design and application of the proposed fiber-reinforced concrete jackets in deficient existing RC beam-column joints provides a sustainable strengthening technique by contributing to the reduction in the cost and to labor-intensive procedures of common jackets by completely replacing the installation of reinforcement.

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.