RC Beam-column Joints Research Articles

Implementation of Highly-Flowable Strain Hardening Fiber Reinforced Concrete in New RC Beam-Column Joints

The purpose of New RC project was aimed to reduce the member sections and increase the available space of high rise buildings by using high strength concrete (f’c > 70 MPa) and high strength rebars (fy > 685 MPa). Material consumptions and member section sizes can be further reduced owing to the upgrade of strength. However, the nature of brittleness of high strength may also cause early cover spalling and other ductility issues. Addition of steel fibers is an alternative as transverse reinforcement. Highly flowable strain hardening fiber reinforced concrete (HF-SHFRC) has excellent workability in the fresh state and exhibits the strain-hardening and multiple cracking characteristics of high performance fiber reinforced cementitious composites (HPFRCC) in their hardened state. The objective of this study is to investigate the feasibility of implementing HF-SHFRC in New RC building systems, particularly for beam-column joints as an alternative of transverse reinforcements. Four full-scale exterior beam-column joints, including two specimens with intensive transverse reinforcements and two specimens made of HF-SHFRC without any stirrup, are tested. Test results show that the HF-SHFRC specimens perform as well as specimens with intensive transverse reinforcements regarding failure mode, ductility, energy dissipation and crack width control. Integration of New RC building systems and HF-SHFRC can assuring construction qualities and further diminish labor work and give infrastructure longer service life, and eventually lower the life-cycle cost.

Simplified analytical model for flexural response of external R.C. frames with smooth rebars

In this paper an analytical model in a closed form able to reproduce the monotonic flexural response of external RC beam-column joints with smooth rebars is presented. The column is subjected to a constant vertical load and the beam to a monotonically increasing lateral force applied at the tip. The model is based on the flexural behavior of the beam and the column determined adopting a concentrated plasticity hinge model including slippage of the main reinforcing bars of the beam. A simplified bilinear moment-axial force domain is assumed to derive the ultimate moment associated with the design axial force. For the joint, a simple truss model is adopted to predict shear strength and panel distortion. Experimental data recently given in the literature referring to the load-deflection response of external RC joints with smooth rebars are utilized to validate the model, showing good agreement. Finally, the proposed model can be considered a useful instrument for preliminary static verification of existing external RC beam-column joints with smooth rebars for both strength and ductility verification.

Study of Seismic Behavior of RC Beam‐Column Joints Strengthened by Sprayed FRP

To study the seismic behavior of RC beam‐column joints strengthened with sprayed FRP, five 1 : 2 reduced‐scale specimens of joints were tested through quasi‐static experiments. The failure modes, hysteretic curves, skeleton curves, strength, deformation, degradation of strength and stiffness, ductility, and energy dissipation capacity were studied. Furthermore, the effect of three main influencing factors including the sprayed FRP thickness, strengthened area, and axial compression ratio was analyzed in this paper as well. The results show that sprayed FRP strengthening can improve the seismic behavior of RC beam‐column joints effectively. The increase of sprayed FRP thickness can lead to a better seismic performance for the joints. Strengthening area can affect the bearing capacity obviously. Higher axial compression ratio can increase the bearing capacity and initial stiffness, but it can make the deformation capacity and ductility decreased. The study can provide references to further research on the sprayed FRP material for strengthening of RC beam‐column joints.

Experimental and numerical investigation on the cyclic behavior of RC beam column joints with EAF slag concrete

An experimental and numerical study about exterior reinforced beam-column joints made with recycled concrete containing Electric Arc Furnace (EAF) slag aggregate, and subject to horizontal reversed cyclic loading, is shown in this paper. Three real scale joints were tested under quasi-static cyclic loading, to study the influence of EAF concrete use on the global behavior of the specimens, in terms of ultimate load, hysteresis response and dissipated energy. The joints exhibited the same failure mode, which involved the shear failure of panel joint and yielding of beam steel longitudinal bars. Then a numerical investigation was carried out, consisting of three-dimensional non-linear finite-element (FE) models, which were validated with the experimental results. Lastly, a parametric study was carried out to understand the effects of column axial load, beam longitudinal reinforcement bar amount and column transverse reinforcement ratio. Results indicate that, in all the analyzed cases, the seismic performance of the joints made with EAF slag concrete is better than with conventional material.

Full Scale Reinforced Concrete Beam-Column Joints Strengthened with Steel Reinforced Polymer Systems

This paper presents the results of an experimental campaign performed at the Laboratory of Materials and Structural Testing of the University of Salerno (Italy) in order to investigate the seismic performance of RC beam-column joints strengthened with Steel Reinforced Polymer (SRP) systems. With the aim to represent typical facade frames’ beam-column subassemblies found in existing RC buildings, specimens were provided with two short beam stubs orthogonal to the main beam and were designed with inadequate seismic details. Five members were strengthened by using two different SRP layouts while the remaining ones were used as benchmarks. Once damaged, two specimens were also repaired, retrofitted with SRP and subjected to cyclic test again. The results of cyclic tests performed on SRP strengthened joints are examined through a comparison with the outcomes of the previous experimental program including companion specimens not provided with transverse beam stubs and strengthened by Carbon Fiber Reinforced Polymer (CFRP) systems. In particular, both qualitative and quantitative considerations about the influence of the confining effect provided by the secondary beams on the joint response, the suitability of all the adopted strengthening solutions (SRP/CFRP systems), the performances and the failure modes experienced in the several cases studied are provided.

High-strength concrete exterior beam-column joints with high-yield strength steel reinforcements

This paper presents the experimental and analytical investigations carried out on high-strength concrete (HSC) beam-column joints with Grade 700 longitudinal rebars in beams and columns. Five full-scale exterior RC beam-column joints with various reinforcement detailing were designed according to the special seismic provisions of ACI 318-14. The variables in test specimens include the concrete compressive strength, yield strengths of reinforcement and the axial compression levels. The test specimens were subjected to constant column axial loading and quasi-static lateral load reversals. The performance of each test assembly was examined in terms of cracking patterns, lateral loading capacity, strain profiles of the reinforcements, secant stiffness, energy dissipation capacity, and the bond performance. All specimens displayed ductile failure mode and it was concluded that the use of high-strength concrete and the applied axial compression loading could improve the bond condition of the specimens. Parametric studies were performed to study the influence of various parameters on the strength, required development lengths and energy dissipation capacity of the specimens. An explanation for the observed cracking pattern and further analytical investigations using a strut-and-tie modeling was conducted.

High-Strength Concrete Interior Beam-Column Joints with High-Yield-Strength Steel Reinforcements

This study presents the experimental and analytical investigations carried out on high-strength concrete beam-column joints with Grade 700 longitudinal bars in beams and columns. Seven full-scale interior RC beam-column joints with various reinforcement detailing were designed according to the specific seismic provisions of current building codes. Test specimen variables included concrete compressive strength, reinforcement yield strength, and axial compression loading level. The test specimens were subjected to constant column axial loading and quasi-static lateral load reversals. The performance of each test assembly was examined in terms of cracking patterns, lateral loading capacity, reinforcement strain profiles, secant stiffness, energy dissipation capacity, joint shear strength, and bond performance. All specimens displayed ductile failure mode and it is concluded that the use of high-strength concrete and applied axial compression loading can improve specimen bond conditions. Parametric studies via finite-element analysis were performed to examine the influence of various parameters on the strength, bond condition, and energy dissipation capacity of the specimens. In addition, a backbone curve model for the shear behavior of the joints is proposed. An explanation for the observed cracking pattern and further analytical investigation on the joint shear capacity of the specimens is presented.

Seismic Behaviors of RC Frame Beam-Column Joints under Acid Rain Circle: A Pilot Experimental Study

ABSTRACTThis research was carried out to investigate the seismic performance of RC beam-column joints under acid rain circle via comparison of energy dissipation behavior and failure mechanism of joints with different corrosion levels and axial compression ratio. At the initial corrosion level, the strength, ductility, and energy consumption of RC beam-column joints improved slightly; at a later stage, the bearing and deformation capacity decreased as the corrosion rate of steel rebars increased. The test shows that with the increasing of the axial compression ratio, the initial stiffness and ultimate bearing capacity of the joints will increasing if the corrosion levels are the same, but the ductility of that will decrease.

Numerical Modelling of Interior RC Beam-Column Joints for Non-Engineered Buildings Strengthened Using Steel Plates

Data examination regarding historical earthquakes in Indonesia has revealed that damages occurred mostly in non-engineered buildings. Many non-engineered buildings have serious design and construction deficiencies in using concrete of inadequate quality and have poor steel reinforcement detailing especially in their beam-column joints. These joints require an effective strengthening technique which is simple to install. This paper presents steel plates to reinforce concrete beam-column joints through numerical studies. The finite element model was developed using ABAQUS. The FEM results were validated by comparisons with previous experimental tests. For this purpose, two RC beam-column joints were analyzed, including original standard beam columns and non-standard steel detailing strengthened with steel plates. The comparison of the results from numerical model indicated that steel plates could increase lateral strength, ductility, energy dissipation and increase the shear strength of the joints.

Seismic Repair and Retrofit of RC Beam–Column Joints Using Stiffened Steel Plates

Evidence from past earthquakes has shown that during significant events, there are always a number of structures that stay stable but experience different forms of damage in their members. Among these members, beam–column joints in the moment frames are more susceptible to seismic loading and may experience different modes of failure. In this paper, stiffened steel plates are used to repair and retrofit a full-scale damaged RC beam–column joint. The retrofit method is based on joint enlargement. A full-scale external beam–column joint is designed and constructed as an ordinary moment resisting frame based on ACI 318M-11 provisions. The structure is then subjected to progressive quasi-static cyclic loading to failure. The damaged joint is then repaired to its former configuration using pressurized epoxy resin and retrofitted by stiffened steel plates. The repaired and retrofitted joint is then subjected to the same cyclic loading protocol to failure. Seismic performance parameters such as strength, stiffness, ductility and energy dissipation capacity of the original joint and the repaired and retrofitted joint are then extracted from their capacity backbone curves and compared. Results show that the proposed repair and retrofit technique not only regenerated the original capacity but also increased capacity and improved the joint performance by relocating the plastic hinge beyond the repaired region.

Investigation of shear strength models for exterior RC beam-column joint

Various models have been proposed by several researchers for predicting the exterior RC beam-column joint shear strength. Most of these models were calibrated and verified with some limited experimental database. From the models it has been identified that the joint shear strength majorly depends on ten governing parameters. In the present paper, detailed investigation of twelve analytical models for predicting shear strength of exterior beam-column joint has been carried out. The study shows the effect of each governing parameter on joint shear strength predicted by various models. It has been observed that the consensus on effect of few of the governing parameters amongst the considered analytical models has not been attained. Moreover, the predicted joint strength by different models varies significantly. Further, the prediction of joint shear strength by these analytical models has also been compared with a set of 200 experimental results from the literature. It has been observed that none of the twelve models are capable of predicting joint shear strength with sufficient accuracy for the complete range of experimental results. The research community has to reconsider the effect of each parameters based on larger set of test results and new improved analytical models should be proposed.

Behavior of Damaged Exterior RC Beam-Column Joints Strengthened by CFRP Composites

This paper presents an experimental investigation on the behavior of retrofitted beam-column joints subjected to reversed cyclic loading. The experimental program comprises 8 external beam-column joint connection subassemblages tested in 2 phases; one was the damaging phase and second was the repairing phase. The Beam-column joints were designed only for gravity loads. The joints had no beam-column joint transverse reinforcement and special stirrups in beam and column critical zones. These Non-Seismically designed (NS) joints were damaged with different levels at the first phase of the experiment. In the second phase, the damaged joints were strengthened with externally bonded carbon-fibre-reinforced polymers (C-FRP) sheets. From the observed responses of the examined specimens it can be deduced that the technique of externally bonded retrofitting (EBR) using C-FRP sheets is appropriate for the rehabilitation of the joints seismic capacity. This technique had a significant improvement of the energy dissipation and the performance level and finally it leads to improved type of damages compared with the damage modes of the specimens during the initial loading. Shortcomings of the application of C-FRP sheets for practical use are also pointed out.

Evaluation of performance of non‐invasive upgrade strategy for beam–column sub‐assemblages of poorly designed structures under seismic type loading

SummaryBeam–column sub‐assemblages are the one of the most vulnerable structural elements to the seismic loading and may lead to devastating consequences. In order to improve the performance of the poorly/under‐designed building structures to the critical loading scenarios, introduction of steel bracing at the RC beam–column joint is found to be one of the modern and implementable techniques. In the present work, a diagonal metallic single haunch/bracing system is introduced at the beam–column joints to provide an alternate load path and to protect the joint zone from extensive damage because of brittle shear failure. In this paper, an investigation is reported on the evaluation of tae influence of different parameters, such as angle of inclination, location of bracing and axial stiffness of the single steel bracing on improving the performance through altering the force transfer mechanism. Numerical investigations on the performance of the beam–column sub‐assemblages have been carried out under cyclic loading using non‐linear finite element analysis. Experimentally validated numerical models (both GLD and upgraded specimen) have been further used for evaluating the performance of various upgrade schemes. Cyclic behaviour of reinforcement, concrete modelling based on fracture energy, bond‐slip relations between concrete and steel reinforcement have been incorporated. The study also includes the numerical investigation of crack and failure patterns, ultimate load carrying capacity, load displacement hysteresis, energy dissipation and ductility. The findings of the present study would be helpful to the engineers to develop suitable, feasible and efficient upgrade schemes for poorly designed structures under seismic loading. Copyright © 2016 John Wiley & Sons, Ltd.

Strengthening and rehabilitation of exterior RC beam–column joints using carbon-FRP jacketing

The scope of this study is to present the results of an experimental investigation of the behavior of shear deficient exterior beam–column joints retrofitted by carbon-fibre-reinforced polymers (CFRP’s). The joints have no transverse reinforcement so they called non-seismic (NS) joints. Four NS-grade of beam–column joints were tested under reversed cyclic loading and compared with one Seismic joint (S-grade specimen). The experimental program was divided into 3 separated phases including the damaging phase, the repairing phase and the retesting phase. In the third phase of the test, the repaired specimens were tested again until they were reached to final capacity. Results are compared in terms of strength, ductility, energy dissipation and stiffness degradation. A repair-ability performance level of the joints was also achieved through damage index assessment. It is shown that repairing the joints using CFRP laminates is not applicable in damage levels higher than the repair-ability performance level. In this case, the seismic behavior of damaged beam–column joints cannot be improved using CFRP laminates. Finally, it can be concluded that the joints tested in this study, will be repaired up to 1.5 % story drift ratio. Both Park and Ang’s and Ghobarah’s damage indices regarded to repair-ability of specimens are also suggested.

Seismic Response of Strengthened RC Beam Column Joints with Haunch Effects

From the study of a large number of buildings, it has been recognized that beam column joint is one of the critical elements of a building system. This element should be designed and detailed properly, especially when the frame is subjected to earthquake loading. Beam column joints are brittle in nature. The breakdown of beam column joint during earthquake is controlled by bond and shear failure mechanism. The main reinforcement of columns just above the joint region, discontinuous bottom beam reinforcement and little or no joint transverse reinforcement are the most critical details of beam column joints in buildings. Therefore, current international code of practices gives more importance to provision of adequate anchorage to longitudinal bars and confinement of core concrete so as to resist shear. Modern codes propose for reduction of seismic forces through provision of special ductility requirements. Details for achieving ductility in reinforced concrete structures are given in IS 13920-1993. In the present study, a two-bay five-storey reinforced cement concrete moment resisting frame for a general building has been analyzed and designed by using STAAD Pro as per IS 1893–2002 code procedures and detailed as per IS 13920-1993 recommendations. An exterior beam column joint has been modelled to 1/5th scale of the prototype and the specimen has been subjected to cyclic loading to study its behaviour during earthquake loading. The experimental programme consists of two interior beam-column joint specimens, one is RC haunch and other one is strengthened RC haunch. The specimens are designated as RC and RCH respectively. In this study key structural issues such as load carrying capacity, load deflection behavior, stiffness degradation, energy dissipation capacity, ductility factor and cracking pattern have also been examined.

Strut-and-tie modelling for the analysis and design of RC beam-column joints

Beam-column joints have been recognised as one of the potentially weaker elements of reinforced concrete moment-resisting frame structures when subjected to seismic lateral loading. Prior earthquake reconnoitring reported the notable damage that can develop from inappropriate beam-column joint design. Design formulae available in building codes and literature differ considerably in functional form, do not consider all of the key variables that affect the joint response, and broadly predict quite different values of shear strength from one another. A mathematical model based on the strut-and-tie model is developed to estimate the shear strength of exterior and interior reinforced concrete beam-column joints. The proposed model leads to an explicit single closed-form expression for computing the shear strength and accounts for the shear stress contributions provided by the diagonal concrete strut and the shear reinforcement (including both joint hoops and column intermediate bars), while considering those variables that significantly affect the behaviour of such joints. Model parameters were calibrated using the experimental results of 454 exterior and interior joints available in the literature. When compared to a number of predictive expressions for the shear strength of joints, the proposed model provides the best fit with the measured shear strength. Further, a set of simple code-oriented design formulae, with conservative predictions, is proposed to facilitate practical engineering design.

Parametric investigation of 3D RC beam–column joint mechanics

This paper presents the experimental and numerical findings of interior and exterior beam–column–slab joints under cyclic lateral loading in two orthogonal directions. Two full-scale interior and one exterior beam–column joint assemblies incorporating floor slabs were subjected to quasi-static cyclic loading and zero column axial loads. The test results from these three models, designed according to building code provisions for ductile moment-resisting frames, were satisfactory in terms of strength and ductility capacity. Parametric studies via the non-linear finite-element approach were performed to study the influence of various parameters on the strength and ductility of three-dimensional beam–column joints. The study confirmed the beneficial effects of incorporating floor slabs and transverse spandrel beams on the behaviour of beam–column joints. The presence of axial compressive load improved the joint shear capacity of the beam–column joints, but a threshold limit should be applied.

New Experimental Setup for Seismic Testing of Exterior RC Beam–Column Joints

Abstract Exterior beam–column joints are commonly tested to investigate the influence of different strengthening and repair techniques on the seismic performances of RC structures. All of the internal forces developing at the ends of the beams and columns need to be applied to the test specimens and these forces need to be proportioned similar to the proportions of the forces in a structure to simulate the conditions of an actual structure during an earthquake. This paper presents a new experimental setup developed to realistically represent the seismic response and behavior of an exterior RC beam–column joint under earthquake excitations. This setup offers a quite economical alternative to the available loading and testing assemblies, made up of several costly loading devices and support fixtures to approximate the conditions of a joint in an earthquake. The present setup was established by using widely-available and inexpensive components to make seismic testing of joints more feasible considering the financial and space limitations of the researchers, particularly in developing countries. The setup also takes into account the influence of the presence of the slab and transverse beams framing into the planar beam–column connection. Three-dimensional exterior RC beam–column connections were successfully tested using this setup.

Modelling of Two Dimensional Reinforced Concrete Beam-Column Joints Subjected to Monotonic Loading

Compared with experimental studies on reinforced concrete joints subjected to monotonic loading under progressive collapse, numerical predictions are much more economic, convenient and efficient. As a general-purpose finite element program, ABAQUS can be employed to simulate the deformation and failure behaviour of RC beam-column joints. When simulating different types of two dimensional beam-column joints, namely knee, exterior and interior joints, it should be noted that the accuracy of the material properties in the numerical models, especially for concrete, are crucial to the accuracy and the reliability of predictions. Therefore, in this study, appropriate specimens subjected to monotonic loading are selected from several series of experimental studies and simulated in ABAQUS. By comparing the predictions with corresponding experimental results, the required material parameters in ABAQUS are calibrated to provide a reference for future RC joint simulations of progressive collapse.

Erratum for “Seismic Rehabilitation of Exterior RC Beam-Column Joints Using Steel Plates, Angles, and Posttensioning Rods” by Ali Arzeytoon, Abdollah Hosseini, and Alireza Goudarzi

The following conference paper should be added to the list of