RC Beam-column Research Articles

Residual behavior of recycled aggregate concrete beam and column after elevated temperatures

This paper presents the results of an experimental study on the residual behavior of reinforced recycled aggregate concrete (RRAC) beam-columns after exposure to elevated temperatures. Two parameters were considered in this test: (a) recycled coarse aggregate (RCA) replacement percentages (i.e. 0, 30, 50, 70 and 100%); (b) high temperatures (i.e. 20, 200, 400, 600, and 800℃). A total of 25 RRAC short columns and 32 RRAC beams were conducted and subjected to different high temperatures for 1 h. After cooling down to ambient temperature, the following basic physical and mechanical properties were then tested and discussed: (a) surface change and mass loss ratio; (b) strength of recycled aggregate concrete (RAC) and steel subjected to elevated temperatures; (c) bearing capacity of beam-columns; (d) load-deformation curve. According to the test results, the law of performance degradation of RRAC beam-columns after exposure to high temperatures is analyzed. Finally, introducing the influence coefficient of RCA replacement percentage and high temperatures, respectively, to correct the calculation formulas of bearing capacity of beam-columns in Chinese Standard, and then the residual bearing capacity of RRAC beam-columns subjected elevated temperatures is calculated according to the modified formulas, the calculated results are in good agreement with the experimental results.

Main factors determining the shear behavior of interior RC beam-column joints

Reinforced concrete beam-column (RCBC) joints of laterally loaded unbraced frames are sometimes controlled by their shear behavior. This behavior relies on multiple and interdependent complex mechanisms. There are already several studies on the influence of some parameters on the shear strength of reinforced concrete joints. However, there are no studies methodically tackling all the most relevant parameters and quantifying their influence on the overall joint behavior, not just on its shear strength. Hence, considering the prohibitive cost of a comprehensive parametric experimental investigation, a nonlinear finite element analysis (NLFEA) was undertaken to identify the key factors affecting the shear behavior of such joints and quantify their influence. The paper presents and discusses the models employed in this NLFEA and the procedure used to deduce the joint behavior from the NLFEA results. Three alternative, or complementary, quantities related to shear are considered when comparing results, namely, the maximum shear stress supported by the joint, the secant shear stiffness at maximum shear stress and the secant shear stiffness in service conditions. Depending on which of these is considered, the lower or higher the relevance of each of the six parameters investigated: transverse reinforcement in the joint, intermediate longitudinal bars and diagonal bars in the column, concrete strength, column axial load and confining elements in transverse direction.

Cyclic performance of RC beam-column joints with mechanical or forging (GPW) splices; an experimental study

Beam-column joints affect the performance of structures remarkably, therefore, finding an appropriate method for their construction has always been one of the major concerns of researchers. In the present study, the influence of incorporating mechanical and forging (gas pressure welding) splices in longitudinal reinforcement bars of beams on the cyclic performance of RC beam-column joints is evaluated experimentally. Totally five RC joints with non-spliced, mechanically (threaded couplers) spliced and forging spliced bars were examined under axial and cyclic loads applied to columns and beams, respectively. Crack propagation of specimens are analyzed and load-drift hysteresis curves are provided as test outputs. Moreover, the influence of the splice method and number of spliced bars on joints’ behavior is assessed in terms of seismic parameters including displacement ductility, stiffness and cumulative absorbed energy. Results showed that forging splices can be considered as an efficient and reliable method for bar splicing and mechanical splices might affect joints’ behavior significantly.

Upgrading of precast RC beam-column joints using innovative FRP/steel hybrid technique for progressive collapse prevention

This study aims at investigating the efficacy of using an innovative hybrid strengthening technique composed of near-surface mounted (NSM) steel rebars along with fiber reinforced polymer (FRP) sheets to prevent (or diminish) the risk of progressive collapse in precast reinforced concrete (RC) beam-column joints. The study details tests involving one control specimen that is a half-scale single-story precast RC beam-column assembly having two bays. One monolithic test specimen with continuous longitudinal beam rebars was employed for comparison. The third specimen was similar to the control one, but it was retrofitted using FRP sheets combined with NSM steel rebars within the beam-column joint zone. The base of the center column was released, and a dynamic load was applied in the vertical direction on this column for simulating the column-removal scenario of progressive collapse. The proposed strengthening technique was efficient at enhancing the peak load and dissipated energy of the upgraded specimen by about 16.9 and 12.4 times, respectively, of control precast specimen. Three dimensional (3D) finite element (FE) models that consider rate-dependent material nonlinearity and bond behavior at FRP-to-concrete interface were also devised to predict the behavior of test specimens. Good agreement was obtained between the experimental and FE results with prediction errors ranging from 0% to 4%, 1% to 17%, and 3% to 10% for peak load, center column displacement at peak load, and dissipated energy at ultimate state. The validated FE models were employed for parametric studies of practical interest for investigating the impact of different strengthening parameters on the behavior of test specimen under the middle column-loss scenario.

Crack assessment of RC beam–column joints subjected to cyclic lateral loading using acoustic emission (AE): the influence of shear links aspect

Existing reinforced concrete (RC) beam–column joints, which are designed mainly to resist gravity load, may encounter serious problems in low to moderate seismic regions. The moderate earthquake in Ranau, Malaysia, affected numerous old buildings, mainly manifesting as uncontrolled crack propagation in RC members at the beam–column joint. Effects of shear reinforcement between shear link spacing on crack formation on four RC beam–column joints were investigated under cyclic lateral loading with acoustic emission (AE) monitoring. The control specimen (BCJ-1), which was designed in BS-8110, showed more irregular cracks thus concrete cover spall was observed at an earlier drift ratio (DR) level than for other specimens with additional shear reinforcement between shear link spacing. Sudden drop of AE hits beyond 2.25% DR level with a significant increase in crack width showed that BCJ-1 was no longer able to resist higher loads due to de-bonding between reinforcement and concrete. From the rise time/amplitude against average frequency (RA-AF) graphs, the mode of failure was determined according to DR stages concerning crack characteristics.

Evaluation of a Macro Lump Plasticity Model for Reinforced Concrete Beam-Column Joint under Cyclic Loading

Lateral deformations of reinforced concrete (RC) frames under extreme seismic excitation are highly affected by the stiffness of their beam-column joints. Numerous models have been proposed to simulate the responses of RC beam-column joint under cyclic loading. Development of RC beam-column joint model based on macro modeling using spring elements becomes more popular because of its considerably simple application for seismic performance evaluation purposes. In this study, a simple modification to previously developed macro-spring element-based model for RC beam-column joint is done and is used to simulate the behavior of seven external and five internal RC joints under cyclic loading in SAP2000. The model consists of several spring elements to define column, beam, joint, and bond-slip responses according to its individual moment-rotation relationships. Overall, the analysis results show that the modified model can simulate well the cyclic behavior of RC beam-column joints when are compared to previously available experimental results

Prediction of Joint Shear Deformation Index of RC Beam–Column Joints

In the analysis of reinforced concrete (RC) buildings, beam–column joints are regarded as rigid nodes. In fact, joint deformation may make a significant difference in the lateral response of RC buildings if joints are not properly designed and detailed. To consider joint flexibility, several types of joint models have been proposed. However, these models require complicated computations, consequently making them challenging to apply in engineering practice. This paper proposed a simple approach for predicting the contribution of the joint deformation to the total deformation of RC interior beam–column joints under critical structural deformations. To develop such a simple and accurate approach, experimental and analytical studies were performed on RC interior beam–column joints. In this study, eight half-scale joint specimens were tested under reversed cyclic loading, and 39 full–scale FE models were constructed, varying the selected key parameters. The experimental and analytical results showed that the “joint shear” is a useful index for the beam–column joints with high shear stress levels of vj>1.7 fc′ but is unsuitable for defining the failure of beam–column joints with medium or low shear stress levels of vj≈1.25–1.7fc′ and vj≈1.0fc′. Based on the results, three equations were developed to predict the joint shear deformation index (SDI) of RC interior beam–column connections corresponding to three different types of failure (i.e., joint failure before beam yielding, joint failure after beam yielding, and beam flexural failure). SDI predictions of the proposed equations correlate well with 50 test results of beam–column joints available from the literature.

Experimental and analytical assessment of different anchorage systems used for CFRP flexurally retrofitted exterior RC beam-column connections

The current study presents the results of an experimental program on the application of carbon-fiber reinforced polymer (CFRP) composites to improve the lateral strength capacity of exterior reinforced concrete (RC) beam-column connections. In such connections, the CFRP composites are bonded onto the top and bottom sides of the beam; however, the presence of the column restricts continuation of FRP composites beyond the end critical sections at the column interface. To provide continuity for composites across the joint, four different anchorage systems have been evaluated through experiments on five half-scale RC connections, comprising an as-built and four retrofitted ones, under reversed cyclic loading. The experimental results demonstrated the superior performance of 180-degree anchor fan among all the tested anchorage systems, leading to a complete plastic hinge relocation along the beam from the column face. Analytical investigation employing a fiber section (FS) modelling approach was also performed and the results validated against the experimental ones. The verified model was then exploited to investigate the effect of FRP composites length along the beam on the structural behavior of RC beam-column connections.

Seismic Performance of RC Beam–Column Joints Constructed with Engineered Cementitious Composites

AbstractThis paper presents experimental and analytical investigations carried out on RC beam–column joints incorporating engineered cementitious composite (ECC) material in the beam–column joint r...

Cyclic performance of RC beam-column joints enhanced with superelastic SMA rebars

Connections play a significant role in strength of structures against earthquake-induced loads. According to the postseismic reports, connection failure is a cause of overall failure in reinforced concrete (RC) structures. Connection failure results in a sudden increase in inter-story drift, followed by early and progressive failure across the entire structure. This article investigated the cyclic performance and behavioral improvement of shape-memory alloy-based connections (SMA-based connections). The novelty of the present work is focused on the effect of shape memory alloy bars is damage reduction, strain recoverability, and cracking distribution of the stated material in RC moment frames under seismic loads using 3D nonlinear static analyses. The present numerical study was verified using two experimental connections. Then, the performance of connections was studied using 14 models with different reinforcement details on a scale of 3:4. The response parameters under study included moment-rotation, secant stiffness, energy dissipation, strain of bar, and moment-curvature of the connection. The connections were simulated using LS-DYNA environment. The models with longitudinal SMA-based bars, as the main bars, could eliminate residual plastic rotations and thus reduce the demand for post-earthquake structural repairs. The flag-shaped stress-strain curve of SMA-based materials resulted in a very slight residual drift in such connections.

An Experimental Study on Behaviors of Beam-Column Joint Wrapped With Aramid Fiber

Concrete is a composite construction material plays a vital role in the construction of the nation’s infrastructure. The failure of the structure are mainly due to the failure of the concrete in beam, column joints.In recent days more technical researches are going on to avoid the beam-column joints failure. In this experiment we add the aramid fiber to check the behavior of beamcolumn joints and externally wrapped with aramid fiber was test to failure. Using an arrangement which transfer horizontal moment to the joints of the beam-column through two opposite cantilever moment arms.Aramid fiber is a class of synthetic fibers and heat resistant. They are fibers in which the strength of the chemical bond can be exploited due to the reason the chain molecules are highly oriented along the fiber axis. The experimental work consist of casting RC beam-column joints in controlled beam-column joints, design for torsion beamcolumn joints, and fully wrapped with aramid fiber beamcolumn joints each 3 specimen and curing this specimen for 7,14,28 days and testing this test specimen under “Loading Frame”.

A Case Study on Structural Failure of Reinforced Concrete Beam-Column Joint After the First Significant Earthquake Impact in Malaysia

This paper presents a case study regarding failures of structural buildings which occurred in Malaysia after the first significant earthquake event dated on June 5, 2015. Ranau is a locality situated in Sabah, Malaysia on the island of Borneo. The seismic activity was triggered when an earthquake with a magnitude of 5.9 afflicted Ranau, including seven other districts that also felt the tremors. Even though the impact of magnitude was undisputedly not high, the severity level of damages was found to be absolute (irreparable) in the structural RC beam-column joints and soft-storey buildings. Most of the buildings in Malaysia were built without the consideration of seismic design, and thus a major factor in structural failure. The earthquake has directed the seismic demand, while the total displacement was concentrated at the weakest floor that caused more damage to the building. This paper shows the causes of beam-column joint damages and explains the proposed (to-date) strengthening methods. Future studies related to seismic activities are in need to analyse the performance of the existing design of structural RC members and propose a seismic design in Malaysia.

Experimental and numerical investigation on cyclic behaviour of RC beam column joints reinforced with geogrid material

This article investigates the effectiveness of geogrid material on upgrading the cyclic performance of nonductile exterior reinforced concrete (RC) beam-column joints by experimental observations and non-linear finite element simulations. Conventional RC beam-column joints without seismic detailing confined internally with geogrid material and compared these specimens with control RC beam-column joint specimens with and without seismic detailing. A detailed 3D non-linear finite element (FE) analyses of the RC beam-column joints internally confined with geogrid in ANSYS are carried out. All the beam-column specimens are subjected to reverse cyclic loading under controlled amplitudes to explore the cyclic performance on the parameters such as failure patterns; load–displacement envelope curve; ductility factor. The test results showed that internal geogrid confinement are effective for enhancing the load-carrying capacity and also ductility of the test specimens. The load–displacement behaviour and damage predicted from finite element analysis almost show the similar behaviour with the experimental result. Hence geogrid with conventional steel bar can be used as a hybrid reinforcement which having excellent ductile behaviour for increasing the seismic performance of RC beam-column joints.

Analysis of slab action on the seismic behavior of external RC beam-column joints

The correct evaluation of beam flexure capacity is of paramount importance in the capacity design process of reinforced concrete (RC) frame structures. Even though few experimental studies on beam-column joints have considered the presence of slab, its action as a tension flange in modifying beam-column strength hierarchy has been clearly found. This is mainly due to the increased hogging moment capacity of beams. Nevertheless, European and Italian seismic codes do not explicitly consider slab action as tension flange nor indicate proper values for effective slab width.To better understand this action, an accurate 3D finite element model has been calibrated based on the results of past experimental tests carried out on a full-scale beam-column joint. Afterwards, the calibrated model has been equipped with a portion of the adjacent spandrel beam and slab in order to evaluate their effect on the beam-column connection's behavior through numerical analyses. Alike previous studies, numerical results show that the tension flange effect of slab can significantly increase hogging (negative) moment in beams framing into beam-column joints. Additionally, it has been found that this effect is a function of slab steel amount, also highlighting the role of slab reinforcement orthogonal to the beam. Based on the above, practical indications have been provided for the evaluation of hogging moment in beams specifically concerning effective slab width to be considered in resisting moment calculations as a function of slab steel amount.

Deformations of reinforced-concrete beam–column joint assemblies

Beam–column joints are generally recognised as critical regions in the analysis and design of moment-resisting reinforced-concrete (RC) frames subjected to both lateral and vertical loads. Such joints should be designed and detailed to ensure that they have adequate overstrength and allow adjacent beams to reach their full ductile capacities. To develop an improved method for predicting the deformation capacity of RC beam–column joint assemblies, the deformation contributions of structural members connecting the joint should be considered. A method is proposed to predict the deformation component ratios of RC beam–column joint assemblies that fail in shear after the adjacent beams have reached their full plastic capacities. The proposed method takes into account the effect of the longitudinal axial strain in the plastic hinge region of beams on the joint longitudinal strain and the strength deterioration of the joint. To verify the deformations of typical RC beam–column joint assemblies estimated using the proposed method, six specimens were tested. Furthermore, 35 experimental results of joints reported in the technical literature were compared with the deformations predicted by the proposed method. Comparisons between the observed and calculated deformations of the considered RC beam–column joint assemblies showed reasonable agreement.

Simplified Approaches for Estimating Yield Rotation of Reinforced Concrete Beam-Column Components

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3D RC beam–column joints retrofitted by joint enlargement using steel angles and post-tensioned bolts

The performance of moment frames in concrete structures is influenced by the behavior of beam-column joints. Experience in past earthquakes has shown that beam-column joints with non-seismic details are highly vulnerable due to the lack of details and transverse reinforcement intervals in the joint core; furthermore, the brittle failure in joints of such type causes overall structural destruction. The present paper focuses on the seismic retrofitting of 3D exterior beam-column joints with no seismic details and considering the effect of slab and transverse beam. For this purpose, four exterior 3D concrete beam-column joint specimens with a scale of 1/2 were constructed and subjected to cyclic loading. The tested specimens comprised two control specimens with and without special seismic details; the two other specimens were retrofitted using angles and post-tensioned bolts. Noteworthy, the effect of initial damage on the cyclic behavior of one of the specimens with retrofit system was further taken into account. All specimens were compared in terms of hysteresis curves and other such parameters as strength, energy dissipation, stiffness reduction, equivalent hysteretic damping, and cracking pattern. The results indicated the efficiency of the retrofit system in enhancing the cyclic behavior of the joints, due to the relocation of shear hinge from the joint core and the formation of flexural plastic hinge in the beam.

Shear Capacity N-M Interaction Envelope for RC Beam-Column Joints with Transverse Reinforcement: A Concept Derived from Strength Hierarchy

ABSTRACT Strength hierarchy assessment method is a capacity analysis procedure that can be used to identify the sequence of failures likely to occur within reinforced concrete (RC) frame buildings under lateral actions such as earthquakes or wind loads. Previous publication on this method mainly focused on the application of this method to (a) the vulnerable RC beam-column joints without any joint shear reinforcement where principal tensile stresses were considered critical, (b) modern RC beam-column joints with joint shear reinforcement where extreme principal compression stresses were considered critical. In this paper, joint shear capacity representation for modern RC beam-column joints (with transverse reinforcements in the joint) is generalized to include both critical components: principal tensile and principal compression stresses. Using strength hierarchy assessment, the investigation showed that it is possible to express the joint shear capacity as an N-M interaction envelope analogous to the N-M interaction of columns. The resulting joint shear capacity N-M interaction concept is validated using a database of 22 external and 22 internal RC beam-column joint tests with joint shear reinforcement at their joint core which resulted in joint shear failure in their tests. Considering the importance of axial load levels on the expected performance of RC beam-column joints, the proposed concept can be used for the general assessment of the joint shear capacity or for beam-column joint modeling purposes, which can be practically used by the design engineers.

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

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

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

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