RC Beam-column Connections Research Articles

Assessment of the impact of column-to-beam strength ratio on seismic response of RC beam-column connections

Beam-column joints play an important role in the overall resistance of reinforced concrete frames during seismic events. The Earthquakes of Al Asnam on October 10, 1980, and Boumerdes on May 21, 2003 in Algeria, have highlighted the failure of beam-column joints as a cause of building collapse. 3D nonlinear finite element analysis with ANSYS software has been used in order to examine exterior RC beam-column joints under monotonic loading. The research has investigated the influence of the value of the column-to-beam strength ratio (CBSR) of these joints on shear strength and seismic performance of concrete structures by changing the height and longitudinal reinforcement of the beam while keeping column dimensions constant. It has been shown that the beam-column depth ratio and the beam longitudinal reinforcement ratio have a significant effect on the shear capacity and seismic behaviour of exterior beam-column joints. An appropriate value of the flexural strength ratio between the column and beam is crucial in order to establish a "strong column-weak beam" mechanism in reinforced concrete frames, because inadequate values can lead to premature failure or reduced shear capacity at the junction. The Algerian seismic code – RPA99/version2003 suggests a minimum value of column-to-beam strength ratio equal to 1.25 at joints for seismic design when building codes in other countries call for higher ratios. Nevertheless, this approach might not accurately represent the actual behaviour and could constrain the optimal performance of structures.

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.

Strengthening of partially ductile RC beam–column connections

Strengthening of partially ductile RC beam–column connections

Experimental Investigation of Cyclic Performance of Slotted RC Beam-Column Connection

Experimental Investigation of Cyclic Performance of Slotted RC Beam-Column Connection

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.

Finite Element Analysis of Reinforced Concrete Interior Beam Column Connection Subjected to Lateral Loading

The 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 interior 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 interior 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.

Experimental assessment of RC beam-column connections with internal and external strengthening techniques

In the last few decades, earthquakes have struck different parts of the world. Recent earthquakes have demonstrated that most of the reinforced concrete structures specially the beam-column joints are vulnerable during earthquakes. The basic requirement of design is that the joint must be stronger than the adjoining hinging members, usually the beams or columns. The existing reinforced concrete beam-column joints which are designed as per code IS 456:2000. Hence the beam-column joints that are not designed as per the ductility code may not perform well when subjected to seismic forces. They must be strengthened in order to improve their performance during earthquakes. Until 1990, concrete jacketing and steel jacketing were the two common methods adopted for strengthening the deficient reinforced concrete beam-column joints. A new technique for strengthening the reinforced concrete structural members is through confinement with an external fiber reinforced polymer sheets. Ansys software are used to model the beam column joint and demonstrate its load carrying capacity. The effectiveness of the strengthening has to be evaluated experimentally. An attempt has been made to carry out an experimental investigation to compare the performance of beam-column joints that are designed as per code IS 456:2000. An experimental investigation has been carried out under static load and reversal load to find the load carrying capacity of reinforced concrete beam-column joint specimens that are detailed as per code IS 456:2000 and retrofitted with Glass Fiber Reinforcement Polymer (GFRP) sheets.

Rehabilitation of exterior RC beam-column connections using epoxy resin injection and galvanized steel wire mesh

The efficacy of a galvanized steel wire mesh (GSWM) as an alternative material for the rehabilitation of RC beamcolumn connections damaged due to reversed cyclic loading was investigated. The repair mainly uses epoxy resin infused under pressure into the damaged zone and then confined using three types of locally available GSWM mesh. The mesh types used herein are (a) Weave type square mesh with 2mm grid opening (GWSM-1) (b) Twisted wire mesh with hexagonal opening of 15 mm (GSWM-2) and (c) welded wire mesh with square opening of 25 mm (GSWM-3). A reduced scale RC beam-column connection detailed as per ductile detailing codes of Indian Standard was considered for the experimental investigation. The rehabilitated specimens were also subjected to similar cyclic displacement. Important parameters related to seismic capacity such as strength, stiffness degradation, energy dissipation, and ductility were evaluated. The rehabilitated connections exhibited equal or better performance and hence the adopted rehabilitation strategies could be considered as satisfactory. Confinement of damaged region using GSWM-1 significantly enhanced the seismic capacity of the connections.

Rehabilitation and strengthening of exterior RC beam-column connections using epoxy resin injection and FRP sheet wrapping: Experimental study

The efficacy of a technique for the rehabilitation and strengthening of RC beam-column connections damaged due to cyclic loading was investigated. The repair mainly uses epoxy resin infused under pressure into the damaged region to retrieved back the lost capacity and then strengthening using fiber reinforced polymer (FRP) sheets for capacity enhancement. Three common types of reduced scale RC exterior beam-column connections namely (a) beam-column connection with beam weak in flexure (BWF) (b) beam-column connections with beam weak in shear (BWS) and (c) beam-column connections with column weak in shear (CWS) subjected to reversed cyclic loading were considered for the experimental investigation. The rehabilitated and strengthened specimens were also subjected to similar cyclic displacement. Important parameters related to seismic capacity such as strength, stiffness degradation, energy dissipation, and ductility were evaluated. The rehabilitated connections exhibited equal or better performance and hence the adopted rehabilitation strategies could be considered as satisfactory. Confinement of damaged region using FRP sheet significantly enhanced the seismic capacity of the connections.

Experimental assessment of fire-exposed RC beam-column connections with varying reinforcement development lengths subjected to column removal

This paper describes an experimental investigation into the behaviour of RC beam-column connections under a column removal scenario induced by fire. A purpose-built hybrid heating furnace is employed to carry out the fire tests on five RC connections with varying reinforcement development lengths, with and without cooling effects. The thermal response of the RC connection specimens, including the temperature field and the axial force-furnace temperature curves, is firstly described. Subsequently, push-down tests are carried out on the beam-column connections, and the horizontal support reactions are closely monitored using a specially-designed sensor system. Based on the experimental results, the joint vertical load-displacement and bending moment-rotation relationships are presented, together with an account of the failure modes observed. The mechanical behaviour is discussed in detail, including the tying and rotation capacity provided by the connection specimens, with emphasis on the effect of the reinforcement development length as well as the heating regime. The experimental capacity interaction curves are also compared with the theoretical prediction for ambient condition, and employed to carry out a detailed examination of the underlying failure mechanisms. Finally, the findings are used to provide practical recommendations for enhancing the structural robustness of structural configurations of the form considered in this study.

Nonlinear modeling of a RC beam-column connection subjected to cyclic loading

When reinforced concrete structures are subjected to strong seismic forces, their beam-column connections are very susceptible to be damaged during the earthquake event. Consequently, structural designers try to fit an important quantity of steel reinforcement inside the connection, complicating its construction without a clear justification for this. The aim of this work is to evaluate –and demonstrate- numerically how the quantity and the array of the internal steel reinforcement influences on the nonlinear response of the RC beam-column connection. For this, two specimens (extracted from an experimental test of 12 RC beam-column connections reported in literature) were modeled in the Finite Element code FEAP considering different stirrup\'s arrays. The nonlinear response of the RC beam-column connection is evaluated taking into account the nonlinear thermodynamic behavior of each component: a damage model is used for concrete; a classical plasticity model is adopted for steel reinforcement; the steel-concrete bonding is considered perfect without degradation. At the end, the experimental responses obtained in the tests are compared to the numerical results, as well as the distribution of shear stresses and damage inside the concrete core of the beam-column connection, which are analyzed for a low and high state of confinement.

Seismic Retrofit of Defective RC Beam-Column Joints

Strong earthquakes always occur in countries with seismic risk and can potentially cause multiple deaths. This study investigates the seismic vulnerability of RC beam-column connections. Generally, it is impractical to simultaneously set up the molds of the concrete beam, ceiling and column and achieve a uniform concrete and this can cause numerous constructional deficiencies. Usually, these deficiencies can be instrumental in the failure of RC frames. Therefore, this study investigates the performance of a defective RC beam-column connection and provides a method to improve the behavior of the connection. The defective connection studied herein belongs to a high school in the city of Kermanshah, Iran. Many factors that affect the performance of the retrofitting designs are studied. Also, all of the parameters used in the analyses were obtained based upon the actual behavior of the material through core extraction and tensile tests. Finally, an optimal design is proposed.

NONLINEAR FINITE ELEMENT ANALYSIS OF NONSEISMICALLY DETAILED INTERIOR RC BEAM-COLUMN CONNECTION UNDER REVERSED CYCLIC LOAD

This paper presents a nonlinear finite element analysis of non-seismically detailed RC beam column connections under reversed cyclic load. The test of half-scale nonductile reinforced concrete beam-column joints was conducted. The tested specimens represented those of the actual mid-rise reinforced concrete frame buildings designed according to the non-seismic provisions of the ACI building code. The test results show that specimens representing small and medium column tributary area failed in brittle joint shear while specimen representing large column tributary area failed by ductile flexure though no ductile reinforcement details were provided. The nonlinear finite element analysis was applied to simulate the behavior of the specimens. The finite element analysis employs the smeared crack approach for modeling beam, column and joint, and employs the discrete crack approach for modeling the interface between beam and joint face. The nonlinear constitutive models of reinforced concrete elements consist of coupled tension-compression model to model normal force orthogonal and parallel to the crack and shear transfer model to capture the shear sliding mechanism. The FEM shows good comparison with test results in terms of load-displacement relations, hysteretic loops, cracking process and the failure mode of the tested specimens. The finite element analysis clarifies that the joint shear failure was caused by the collapse of principal diagonal concrete strut.

Effect of loading rates on the behaviour of epoxy-repaired RC beam–column connections

Reduced-scale external RC beam–column specimens with three typical deficiencies as beam weak in flexure (BWF), beam weak in shear (BWS) and column weak in shear (CWS) were tested under cyclic excitations of different frequencies, varying from .025 to 1.0 Hz. These damaged specimens were repaired using epoxy resin injection. Parameters like load carrying capacity, stiffness degradation and energy dissipation were monitored for exploring the effect of rate of loading on all the beam–column connections in a holistic manner. The repaired connections exhibited equal or marginally better performance and hence the adopted repairing strategies could be considered as satisfactory. Test results also showed that faster rate of loading produced fewer and more localised cracks on the specimens than those at the slower rate. Test results further showed that the rate effect is significant in beam–column connection with BWF, while the same is not so significant in BWS and CWS specimens.

Experimental fragility functions for exterior deficient RC beam-column connections before and after rehabilitation

The paper presents the development of experimental fragility functions for exterior RC beam-column connections based on results obtained from extensive testing carried out in the present study. Three typical types of seismically deficient beam-column connections, which are commonly prevalent in Indian sub-continent, were considered. These specimens were tested under cyclic displacement histories with different characteristics to induce different damage states. Rehabilitation specific fragility functions for damaged specimens were developed considering drift angle as a demand parameter. Four probability distributions were fit to the data and suitability of each distribution was evaluated using standard statistical method. Specimens with different damage states were rehabilitated appropriately and rehabilitated specimens were tested under similar displacement histories. Fragility functions for rehabilitated specimens have also been developed following similar procedure. Comparison of fragility functions for both original and rehabilitated specimens for each rehabilitation method showed close agreement, which establishes the effectiveness of the adopted rehabilitation strategies and hence would provide confidence in field application.

PERFORMANCE OF REINFORCED CONCRETE BEAM COLUMN CONNECTIONS EXPOSED TO FIRE UNDER CYCLIC LOADING

ABSTRACTFire could dramatically reduces the characteristic strength of the reinforced concrete elements [1,2]. A lot of efforts has been devoted to study the effect of fire on the reinforced concrete elements during past decades. These previous studies focused on evaluating fire resistance for concrete elements, [3] and provide some recommendations of structural fire-resistance [4] such as cover thickness, reinforcement ratio and coating materials. A lot of research focused on RC columns [5,6,7], beams [8] and slabs [9] which has been exposed to fire, where less efforts aimed to study the effect of fire on RC beam column connections [10,11,12].The main objective of the present work is to study the structural behavior of reinforced concrete beam-column connections exposed to fire under cyclic loading [13,14] and to evaluate the reduction in concrete strength during fire process. To achieve these goals, this research consists of two parts, the first part is experimental program, and the second is the theoretical analysis. The experimental program include 12 one- third scale specimens half of them casted from normal concrete and other half from SCC. The effect of some parameters on the connection's behavior like reinforcement ratio, type of concrete (normal or self-compacted concrete) [15] and exposure fire time were studied. Experimental program extended also to study heat distribution inside RC beam–column connections by measuring temperature at 65 point Distributors at 5 sections all over the RC connection. Theoretical analysis was done by using finite element program (ANSYS12.1) and a comparison between experimental program and theoretical analysis was done SCC showed good properties in hardening state when exposed to high temperature compared with normal concrete [16]. Increasing reinforcement ratio of RC connections increases its fire resistance Good agreement between analytical and experimental work was observed.

Effect of Cyclic Loading Frequency on the Behavior of External RC Beam-Column Connections

Reduced-scale external RC beam-column specimens with three typical deficiencies as beam weak in flexure (BWF), beam weak in shear (BWS) and column weak in shear (CWS) were tested under cyclic excitations of different frequencies, varying from 0.025–2.0 Hz. Parameters like load carrying capacity, stiffness degradation, energy dissipation, principal tensile stress were monitored for exploring the effect of rate of loading on different types of deficient beam-column connections in a holistic manner. Test results showed that the rate effect is significant in beam-column connection with BWF, while the same is not so significant in BWS and CWS specimens.

An experimental study on the effect of PET fibers on the behavior of exterior RC beam-column connection subjected to reversed cyclic loading

An experimental study has been conducted on reduced-scale exterior RC beam-column connections to investigate its behavior due to the addition of Polyethylene terephthalate (PET) fiber-reinforced concrete, i.e., PFRC at the joint region. PET fiber (aspect ratio=25) of 0.5% by weight of concrete used in the PFRC mix was obtained by hand cutting of post-consumer PET bottles. Three reference specimens were cast and subjected to reverse cyclic loading. Additionally, PFRC specimens were also cast and subjected to similar cyclic displacement. Comparing the results, PFRC specimens improved the damage tolerance, load resisting capacity, stiffness degradation, ductility, and energy dissipation of the specimens. Further, PFRC specimens also presented a lower damage indices and higher principal tensile stresses as compared to the reference specimens. The results obtained gave experimental evidence of the suitability of PET fibers as a discrete reinforcement in substitution of steel fiber for structural use.

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.