Reinforced Concrete Beam-column Joints Research Articles

EXPERIMENTAL STUDY OF RC BEAM-COLUMN JOINT RETROFITTED BY BFRP GRID WITH HIGH STRENGTH MORTAR

The reinforced concrete (RC) beam-column joint is a critical member of the building. Its failure can make the structure collapse abruptly. The failure of joints mostly occurred in the structure built before the 1970s because of poor design and inadequate reinforcement detailing. To date, numerous research has been conducted to enhance the performance of the joint in terms of failure mode, strength, and ductility by externally retrofitting using bonded fiber-reinforced polymer (FRP) technique. Nonetheless, using bonded FRP technique encounters some drawbacks such as debonding and inadequate performance under moist and flammable environments. To overcome this, epoxy is replaced by a cementitious matrix. In this study, a RC beam-column joint is fabricated in 2/3 scale following an existing structure. The specimen is retrofitted using Basalt Fiber Reinforced Polymer (BFRP) grid with the combination of the cementitious matrix using high strength mortar. The dimension of the retrofitted specimen is intentionally kept the same by taking out the concrete cover where the cementitious matrix is employed. As the result, the overall performance of the specimen is improved. The specimen becomes stronger and can withstand longer applied displacement before it collapsed.

Review of Modeling Techniques for Analysis and Assessment of RC Beam-Column Joints Subjected to Seismic Loads.

Beam-column connections are the most critical components of reinforced concrete (RC) structures. They serve as a load transfer path and take a significant portion of the overall shear. Joints in RC structures constructed with no seismic provisions have an insufficient capacity and ductility under lateral loading and can cause the progressive failure of the entire structure. The joint may fail in the shear prior to the connecting beam and column elements. Therefore, several modeling techniques have been devised in the past to capture the non-linear response of such joints. Modeling techniques used to capture the non-linear response of reinforced-concrete-beam-column joints range from simplified lumped plasticity models to detailed fiber-based finite element (FE) models. The macro-modeling technique for joint modeling is highly efficient in terms of the computational effort, analysis time, and computer memory requirements, and is one of the most widely used modeling techniques. The non-linear shear response of the joint panel and interface bond-slip mechanism are concentrated in zero-length linear and rotational springs while the connecting elements are modeled through elastic elements. The shear response of joint panels has also been captured through rigid panel boundary elements with rotational springs. The computational efficiency of these models is significantly high compared to continuum models, as each joint act as a separate supe-element. This paper aims to provide an up-to-date review of macro-modeling techniques for the analysis and assessment of RC-beam-column connections subjected to lateral loads. A thorough understanding of existing models is necessary for developing new mechanically adequate and computationally efficient joint models for the analysis and assessment of deficient RC connections. This paper will provide a basis for further research on the topic and will assist in the modification and optimization of existing models. As each model is critically evaluated, and their respective capabilities and limitations are explored, it should help researchers to improve and build on modeling techniques both in terms of accuracy and computational efficiency.

Behavior of Smart Reinforced Concrete Beam Column Joints by Using Shape Memory Alloy Reinforcement Under Repeated Loading

Using the super elastic materials in structures design is becoming very important in the research field because of their rare ability in sensing the around effect and reacting against the mechanical and thermal react. The major intent in this research is designing smart concrete beam column joints reinforced by Shape Memory Alloy (SMA) bars. The suggested systems use the (super elastic) Pseudo Elastic (PE) react of the SMA as reinforcement after being subjected under monotonic and repeated load. The behaviors of systems were explored experimentally and by using finite element simulation. In order to estimate load-displacement relationships of these specimens in this study, Analytical models were developed. A comparison of the reinforced specimens by SMA was carried out and it contained that the variation in percentage of the SMA in flexural reinforcement (25%, 50%, 75%) of the total flexural reinforcement by using this substitution get a clear effect on the failure load and the ultimate displacement of the specimens with these different ratios. The Finite Element models were developed by using the software ABAQUS. The models have been checked with the experimental results in the load-displacement terms in the top reinforcement. The models showed reasonable response. Where the ultimate load decreased by using SMA bars in (25%, 50%, 75% ) percentage of total flexural reinforcement about (50.51%, 28.32%, 38.15%) respectively, in case of static loading and (20.7%, 10.7%, 9.3%) respectively in case of repeated loading, and the deflection is increasing by using SMA in (25%, 50%, 75% ) percentage of total flexural reinforcement about (1.2%, 8.4%, 0.36%) respectively, in case of static loading and (9.6%, 5.28%, 10.9%) respectively in case of repeated loading

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.

Comparative Assessment of Shear Demand for RC Beam-Column Joints under Earthquake Loading

This paper focuses on the evaluation of bi-axial shear demand for reinforced concrete (RC) beam–column joints assuming: (i) the SPEAR frame as a benchmark; and (ii) different structural analysis methods which share the same seismic input. A numerical model was implemented using lumped plasticity. The joints were modeled as rigid offsets of beams and columns. The shear demand at a joint is evaluated as a post-process of the beam’s nodal moment. The discussion focuses on the differences between the estimated shear demand considering modal-response-spectrum analysis (MRSA), non-linear static analysis (NLSA) and non-linear time history (NLTH). Strength assessment of joints is discussed as well. Significant strength differences were recognized by using different building codes targeted to existing structures which, in general, behaved on the safe side. The elliptical shear strength domain resulted in being conservative when compared to NLTH shear demand orbits. NLSA, using modal combination, proved to estimate the larger shear demand with respect to MRSA and NLTH.

Influence of stirrup ratio on size effect of shear strength of concrete beam-column joints reinforced with CFRP bars

<p indent="0mm">The shear failure behavior and the size effect of shear strength of carbon fiber-reinforced plastic (CFRP)-reinforced concrete beam-column joints are investigated in this study. The finite element model for failure analysis of CFRP-reinforced concrete beam-column joints was established using a mesoscale numerical method. The mesoscale failure mode and failure mechanism of geometrically similar CFRP-reinforced concrete beam-column joints were studied, and the influence of CFRP-bar ratio on shear strength and size effect law of joints was discussed. The simulation results show that the nominal shear strength of CFRP-reinforced concrete beam-column joints has an obvious size effect, and the size effect of shear strength can be alleviated by increasing the CFRP-bar ratio. In addition, it is found that the size effect of the nominal shear strength of concrete beam-column joints with CFRP bars is more obvious than that of reinforced concrete (RC) beam-column joints. Based on the size effect law of nominal shear strength for RC beam-column joints, considering the effect of stirrup ratio proposed in the previous work, along with the numerical test results in this study, the size effect law was extended and established for the analysis of nominal shear strength of concrete beam-column joints with CFRP bars.

Bond Slip in Reinforced Concrete Beam–Column Joints — A Semi-Empirical Implicit Modeling and Possible Influence of Design Standard Compliance

Bond slip in RC beam–column joints may affect the seismic response or performance assessment of structures considerably. Explicit macroscopic models that satisfy the joint kinematics can be incorporated within a frame model to numerically account for the effect of bond slip. Seismic performance assessment of buildings generally rules out the explicit modeling owing to the associated computational cost. Simplified implicit models are instead preferred owing to the ease of implementation in a commercial finite element (FE) provided the model parameters are calibrated experimentally. Extrapolation of the calibration is generally not valid in other cases with different geometry, sizes and even loading protocols. Most commercial software do not offer the features to explicitly modeling the bond slip. Numerical modeling of bond slip is proposed in this paper that can be conveniently implemented in a commercial software such as Seismostruct. Unlike the prior art, the slip parameter can be extracted using a semiempirical approach preceded by the generation of a numerical database. The proposed framework is also validated against the experimental results of one exterior and one interior beam–column joints. Sample illustration on an example building designed against the same seismic hazard level but following the recommendations per IS 13920, ACI 318 and EC8 is considered for monotonic (without bond slip) and cyclic (with bond slip) pushover analyses. Consideration of bond slip initiates early yielding and results in reduction of secant stiffness at the onset of yielding. The extent of influence depends on the compliance of design standards. For example, relatively higher percentage of reinforcement when designed per IS 13920 (as compared to ACI 318 and EC8) leads to a somewhat lower slip parameter resulting in lesser yield displacement and reduction of secant stiffness at the onset of yielding.

Behaviour of Hybrid Fibre-Reinforced Ternary Blend Geopolymer Concrete Beam-Column Joints under Reverse Cyclic Loading.

Beam–column joints are extremely vulnerable to lateral and vertical loads in reinforced concrete (RC) structures. This insufficiency in joint performance can lead to the failure of the whole structure in the event of unforeseen seismic and wind loads. This experimental work was conducted to study the behaviour of ternary blend geopolymer concrete (TGPC) beam-column joints with the addition of hybrid fibres, viz., steel and polypropylene fibres, under reverse cyclic loads. Nine RC beam-column joints were prepared and tested under reverse cyclic loading to recreate the conditions during an earthquake. M55 grade TGPC was designed and used in this present study. The primary parameters studied in this experimental investigation were the volume fractions of steel fibres (0.5% and 1.0%) and polypropylene fibres, viz., 0.1 to 0.25%, with an increment of 0.05%. In this study, the properties of hybrid fibre-reinforced ternary blend geopolymer concrete (HTGPC) beam-column joints, such as their ductility, energy absorption capacity, initial crack load and peak load carrying capacity, were investigated. The test results imply that the hybridisation of fibres effectively enhances the joint performance of TGPC. Also, an effort was made to compare the shear strength of HTGPC beam-column connections with existing equations from the literature. As the available models did not match the actual test results, a method was performed to obtain the shear strength of HTGPC beam-column connections. The developed equation was found to compare convincingly with the experimental test results.

Experimental study of reinforced concrete beam-column joint retrofitted by CFRP grid with ECC and high strength mortar

The failure of a reinforced concrete (RC) beam–column joint during an earthquake can lead to the progressive collapse of the entire structure. This type of failure, which has been mainly observed among structures built prior to the 1970s, occurs due to poor design and inadequate detailing of rebars. Recently, a number of researchers have conducted numerous experiments to improve the overall performance of beam–column joints in terms of strength, ductility, and failure mode using the externally bonded fiber-reinforced polymer technique. However, because epoxy is employed, this method encounters problems, such as debonding and inadequate performance under flammable and moist environments. To resolve the foregoing, a cementitious matrix is utilized to replace the epoxy. Four RC beam–column joints are retrofitted using two different techniques employing carbon fiber-reinforced polymer (CFRP) grid covered with engineered cementitious composites (ECC) and high strength mortar. The dimensions of the retrofitted specimens are retained by removing the concrete cover of the joint where the cementitious matrix is applied. The results show that the failure mode of specimens can be modified by shifting the load concentration from the joint to the beam. Furthermore, the overall performance of specimens in term of strength improves. The specimens also exhibit greater ductility; hence, they are capable of delaying failure.

Experimental investigations of resilient hybrid fiber reinforced SCC beam-column subassemblies under cyclic loadings

Fiber is not only minimizing the temperature and shrinkage cracks, but also increases the strength and toughness of the concrete. In this paper, steel fiber (SF) and areca leaf sheath (ALS) fiber have been introduced to enhance the overall performance of concrete in terms of ultimate strength, ductility, energy dissipation, and stiffness degradation. For this purpose, a one-third scaled reinforced concrete beam-column joint (RCBCJ) has been cast as the control specimen. Steel fiber reinforced concrete beam-column joints (SFRCBCJ) with volume fractions 1%, 2%, 3% and 4%; areca leaf sheath fiber reinforced concrete beam-column joints (ALSFRCBCJ) with volume fractions 1%, 2%, 3%, and 4%, and steel-areca hybrid fiber reinforced concrete beam-column joints (SAHFRCBCJ) (1:1 ratio) with volume fractions 1%, 2%, 3% and 4% have been cast. The joints were tested under cyclic loading using a large-scale actuator. It has been observed that the incorporation of SF and AL fibers has significantly enhanced the resilience and performance of joints in terms of ductility, ultimate load carrying capacity, stiffness degradation, and energy dissipation for all SFRCBCJ, ALSFRCBCJ, and SAHFRCBCJ specimens. However, the SAHFRCBCJ specimens have shown the optimum results in terms of performance and economical perspective compared to the other specimens. From the experiments, it has been observed that SFRCBCJ shows 27% higher load carrying capacity, 87% more dissipated hysteretic energy absorption capacity, 81% higher stiffness, and 41% higher ductility compared to RCBCJ subassemblies.

Deformation Capacity of RC Beam-Column Joints Strengthened with Ferrocement

Beam-column joints constructed in the pre-seismic building code do not provide transverse reinforcement and good reinforcement detailing within the region. These cause the occurrence of brittle shear failure, which is one of the factors affecting the number of reinforced concrete (RC) moment resistance building structures collapsing during an earthquake. Therefore, in this study a brittle beam-column joint with a non-seismic building code was designed and strengthened by a ferrocement. Four layers of wire mesh with a diameter of 1 mm and a mesh size of 25.4 mm were installed on both sides of the beam-column joint and cement mortar was cast on it. As a comparison, a ductile beam-column joint was also designed following the current building code, which considers seismic effects. The test results by applying reversed cyclic loading at the beam tip showed that strengthening using ferrocement prevents crack propagation, increasing the deformation capacity, ductility, stiffness, and energy dissipation of beam column joint which are higher than those of the beam-column joint which is designed following the current building code. However, the strengthening does not improve the load carrying capacity significantly.

Effectiveness and Efficiency of Externally Bonded CFRP Sheets for Shear Strengthening of RC Beam-Column Joints.

To develop feasible carbon fiber reinforced polymer (CFRP) retrofit schemes for the shear strengthening of real three-dimensional reinforced concrete (RC) beam-column joints, a series of parameters in relation to the contributions of the CFRP sheets externally bonded to joint panels was numerically investigated in this study. The parameters include CFRP reinforcement ratio, CFRP layout, transverse beam-to-joint panel width ratio, transverse beam-to-joint panel height ratio, location of transverse beam, and number of transverse beams. Strengthening efficiency, a new dimensionless index, was introduced to evaluate the residual effect of a CFRP-strengthening system weakened by the presence of transverse beams in comparison with the increase in joint shear capacity in relation to the one-way counterpart. The results obtained from 44 nonlinear finite element models, which were calibrated against experimental observations, confirmed the effectiveness of the CFRP strengthening technique with regard to the relatively wide ranges of the parameters. The significant differences among the roles of the parameters were revealed, and the reasons behind the differences were analyzed. Furthermore, the shear mechanism of the CFRP-retrofitted joint panels was discussed with the proposed strut-and-tie model.

Prediction of the shear strength of RC beam-column joints using new ANN formulations

Beam-column joint is a key part for reinforced concrete (RC) frame building structures under the impact of severe lateral actions of seismic or wind loading. Prior works indicate that there is lacking in the direction of formulation of new mathematical models to predict RC joints strength by artificial neural network (ANN) considering influential design parameters. Present endeavor is devoted to establish new empirical ANN models to estimate shear strength and failure mode for RC exterior and interior beam-column joints. These models were relied on training, testing and validation of a database of over 200 experiments, for the performance of RC joints, using ANN. More than 20 parameters, related to the geometry and loading of the joints, were selected as inputs for these models; but four effective inputs were used in the formulation of the final ANN models. The outputs for ANN models were compared to those counterparts of the commonly utilized models given in codes and other recent studies. This calculation confirms the reliability of current ANN mathematical models and their outstanding performance. Moreover, comparison shows that the proposed models were precise in including the effective independent variables in these models and avoiding the shortcoming of previous models.

Rehabilitation of seismic-damaged reinforced concrete beam-column joints with different corrosion rates using basalt fiber-reinforced polymer sheets

Reinforcement corrosion and seismic damage considerably affect the seismic performance of reinforced concrete (RC) members. In present research, five RC beam-column joints were designed and tested under cyclic loadings. These joints included one reference specimen, one uncorroded specimen rehabilitated with basalt fiber-reinforced polymer (BFRP) sheets, as well as three seismic-damaged corroded specimens with corrosion rates of 0, 3%, and 9% rehabilitated with BFRP sheets. The seismic behavior of tested specimens, involving the hysteretic responses, ductility, and energy dissipation was discussed. Test results demonstrated that the seismic behaviors of seismic-damaged corroded specimens were effectually upgraded after being rehabilitated with BFRP sheets. The spalling and crushing of concrete, as well as the buckling of stirrups were postponed by the utilization of BFRP sheets, while ductile behaviors of rehabilitated specimens could be observed in the test. Besides, the ultimate displacements, final stiffness, and total cumulative energy dissipation of the rehabilitated specimens were considerably improved with the maximum increase of 14.9%, 16.7%, and 23.3%, respectively. Equations considering the influences of reinforcement corrosion, seismic damage, and FRP rehabilitation on the shear strength of the core area of RC joints rehabilitated with FRP sheets were proposed, and good agreements could be found between the theoretical and experimental results.

Development of an Analytical Model for the FRP Retrofitted Deficient Interior Reinforced Concrete Beam-Column Joints

Beam-column joints (BCJs) constructed until the 1970s carry a low shear capability due to the absence of shear reinforcement. Fiber-reinforced polymers (FRP) are more reliable than other materials to strengthen a weak BCJ. To date, plenty of analytical models have been developed to analyze the actual contribution of the FRP to the shear strength of RC BCJs. However, the models developed are either too complex in computational efforts or based on empirical coefficients that result in compromised results. The models that formulate the contribution of FRP to the shear strength of the FRP-strengthened deficient interior BCJ are very limited, and such models are too complex. An adequate BCJs’ FRP strain equation must still be developed to address these issues. Therefore, the FRP effective strain equation and contribution of FRP to RC BCJs are derived in this research work using an updated database of the appropriate BCJs. The initial analytical model of Bousselham, which Del Vecchio later improved, is further extended to FRP-strengthened deficient interior BCJs. For this purpose, an updated database of the 32 tests around the world of FRP-strengthened interior BCJs deficient in seismic reinforcement is prepared. Firstly, the experimental effective FRP strain is derived using the experimental database. Then, a power-type equation is derived for the effective FRP strain by considering the crucial parameters of the FRP-strengthened interior BCJs. Finally, the experimental shear strengths and those determined with the proposed equation of the FRP-strengthened joints are compared. The average ratio between the experimental and analytical (proposed model) joint shear strengths of the considered specimens ensured the accuracy of the suggested model. The suggested approach makes computing the FRP enhancements required to avoid shear failure in interior joints easy and reliable for researchers and field engineers interested in seismically reinforcing existing structures.

Seismic Performance of Interior Reinforced Concrete Beam–Column Joint with Corroded Reinforcement

This study presented an experimental and analytical investigation on the seismic behavior of a reinforced concrete (RC) interior joint with corroded reinforcements. A total of eight RC interior joints with similar reinforcing detailing were tested and subjected to lateral cyclic loading. The variables studied in this research were the corrosion level of reinforcements in terms of mass loss and the column axial force ratio. The cyclic performance of all the joints including crack pattern, lateral loading capacity, energy dissipation, and lateral displacement decomposition were examined. The corroded joint constitutive model was calibrated and validated using the finite-element method. An analytical strut-and-tie model (STM) was developed for explaining the internal force flow and further parametric investigations. Results indicated that corrosion of reinforcements had a substantial effect on the strength and lateral drift capacity of the joints. In addition, based on the STM model, the axial force ratio exceeding 0.3 and longitudinal reinforcement corrosion level around 6–10% were detrimental toward joint behavior and can contribute to joint shear failure.

Cyclic behavior of interior RC beam-column joints strengthened with NSM-CFRP ropes

Beam-column joints in existing concrete structures could become unsafe for many reasons, such as design error and seismic loading. Thus, in this study, the effectiveness of near surface mounted carbon reinforced polymer (NSM-CFRP) ropes for enhancing interior reinforced concrete (RC) beam-column joints was investigated. Five interior one-third scale RC beam-column joints without transverse reinforcement (stirrups) at the beam-column joints were tested under cyclic loading. The first specimen was tested as a control beam-column joint, while the four remaining beam-column joints were strengthened using NSM-CFRP ropes with a variety of CFRP rope configurations. Results were drawn based on hysteretic curves, envelope curves (load vs. drift ratio), energy dissipation, stiffness, ductility index and failure modes. The results showed that the stiffness and yield load of strengthened beam-column joints was improved compared with the control beam-column joint. The use of NSM-CFRP ropes resulted in an increase in the yield load of the strengthened beam-column joints ranging from 118.7% to 164.1% than the control beam-column joint depending on the NSM-CFRP ropes’ number and its position. The use of X- shaped rope with two ropes on each side of beam and two on each side of column imparted the best effectiveness on stiffness and yield load, for instance, the stiffness increased by 236.7% compared to control beam-column joint. Finally, the bond slip occurred between the rope and concrete; therefore, the rope was only effective before the drift ratio reached 1%-1.5%, therefore, the maximum load is only affected by the RC.

The Influence of α-Fe2O3 Nanoparticles on the Reinforced Concrete Beam–Column Joint Under Cyclic Loading

The Influence of α-Fe2O3 Nanoparticles on the Reinforced Concrete Beam–Column Joint Under Cyclic Loading

A comparison of machine learning- and regression-based models for predicting ductility ratio of RC beam-column joints

Seismic response of Reinforced Concrete (RC) beam-column joints has always been evaluated by researchers due to their undeniable influence on the overall behavior of RC building frames under seismic loads. In the present study, an attempt has been made to predict displacement ductility ratio of RC joints using machine learning- (Artificial Neural Network and Random Forest) and regression-based (linear, nonlinear and ridge) methods. Therefore, a dataset including the results of over 170 experimental studies conducted on RC joints was collected from the international peer-reviewed publications. Parameters reflecting beam and column dimensions (length, cross section width and depth), reinforcement detailing (longitudinal and transverse reinforcement of beams and columns), material properties (concrete compressive strength, yield strength of longitudinal and transverse reinforcement) and retrofitting techniques were considered as input variables for predicting the only output parameter, displacement ductility ratio. The predicted and actual values were compared together and the efficiency of the models was assessed by Taylor diagram and performance metrics including RSME, MAE, MAPE and R2. The evaluation results proved the high reliability of proposed models for predicting ductility of RC joints.

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.