Exterior Reinforced Concrete Beam-Column Joints Research Articles

Improved strut-and-tie method for 2D RC beam-column joints under monotonic loading

In the previous analytical studies on 2D reinforced concrete (RC) beam-column joints, the modified compression field theory (MCFT) and the strut-and-tie method (STM) are usually employed. In this paper, the limitations of these analytical models for RC joint applications are reviewed. Essentially for predictions of RC joint shear behaviour, the MCFT is not applicable, while the STM can only predict the ultimate shear strength. To eliminate these limitations, an improved STM is derived and applied to some commonly encountered 2D joints, viz., interior and exterior joints, subjected to monotonic loading. Compared with the other STMs, the most attracting novelty of the proposed improved STM is that all critical stages of the shear stress-strain relationships for RC joints can be predicted, which cover the stages characterized by concrete cracking, transverse reinforcement yielding and concrete strut crushing. For validation and demonstration of superiority, the shear stress-strain relationships of interior and exterior RC beam-column joints from published experimental studies are employed and compared with the predictions by the proposed improved STM and other widely-used analytical models, such as the MCFT and STM.

Seismic Behaviour of Exterior Reinforced Concrete Beam-Column Joints in High Performance Concrete Using Metakaolin and Partial Replacement with Quarry Dust

Recent earthquakes have demonstrated that most of the reinforced concrete structures were severely damaged; the beam-column joints, being the lateral and vertical load resisting members in reinforced concrete structures, are particularly vulnerable to failures during earthquakes. The existing reinforced concrete beam-column joints are not designed as per code IS13920:1993. Investigation of high performance concrete (HPC) joints with conventional concrete (CC) joints (exterior beam-column) was performed by comparing various reinforcement detailing schemes. Ten specimens were considered in this investigation and the results were compared: four specimens with CC (with and without seismic detailing), four specimens with HPC (with and without seismic detailing), and two specimens with HPC at confinement joint. The test was conducted for lateral load displacement, hysteresis loop, load ratio, percent of initial stiffness versus displacement curve, total energy dissipation, strain in beam main bars, and crack pattern. The results reveal that HPC with seismic detailing will be better compared with other reinforcements details under cyclic loading and reverse cyclic loading.

Experimental Investigation of Exterior RC Beam-Column Joints Retrofitted with FRP Systems

Premature brittle failures because of seismic actions strongly affect the behavior of existing reinforced concrete (RC) structural systems. They commonly involve exterior beam-column joints of structures designed without transverse reinforcement. This paper investigates the behavior of unconfined joints that do not conform to current seismic codes and the effectiveness of externally bonded fiber-reinforced polymers (FRPs) as a strengthening technique. It presents an experimental program carried out on six full-scale RC corner joints under constant axial load and transverse cyclic loading in the as-built and FRP-strengthened configuration. After describing the specimen design strategy and test setup, seismic performance is compared. Particular attention is paid to comparing the experimental capacity of as-built joints and the capacity, which can be predicted on the basis of models available in the literature. Finally, a discussion on the effectiveness of different FRP-strengthening layouts is reported.

Seismic Performance of Lightly Reinforced Concrete Exterior Beam-Column Joints

This paper presents the experimental results of four lightly Reinforced Concrete (RC) exterior beam-column joints with and without beam stubs under cyclic loading with constant column axial force applied at the top of the column. The parameter investigated was the type of reinforcement used in the beam, i.e. plain and deformed bars. Test results showed that when the hooks anchored down in the column increased the tensile stress in the diagonal concrete strut in the joint core, this led to diagonal crack of the concrete and a decrease in the joint shear strength. The seismic performance of the exterior RC joints without beam stub was also observed to be much improved when the hook tail of beam reinforcements was bent inside the joint core. The strut-and-tie model based on the recorded strain in the joint transverse reinforcement could be used to determine the force flow in the joint core.

Numerical Investigations on the Seismic Behavior of FRP and TRM Upgraded RC Exterior Beam-Column Joints

AbstractIn this paper, a detailed procedure for nonlinear finite-element analysis of fiber reinforced polymer (FRP) and textile reinforced mortar (TRM) upgraded reinforced concrete (RC) beam-column exterior joints is presented for predicting their seismic performance under simulated earthquake loading. The finite-element (FE) model was developed using a smeared cracking approach for concrete and three-dimensional layered elements for the FRP and TRM-composites. The results obtained from FE analysis were compared with the test results. The tests were conducted on four as-built exterior beam-column joint specimens under simulated seismic loads. Out of these four specimens, one specimen was tested as a control specimen and the other three were tested after strengthening with TRM, carbon FRP, and glass FRP sheets, respectively. The FE results were compared with the test results through load-displacement behavior, ultimate loads, and crack pattern. Comparison of FE results with the experimentally observed resp...

Effects of Variation of Axial Load and Bidirectional Loading on Seismic Performance of GFRP Retrofitted Reinforced Concrete Exterior Beam-Column Joints

Most of the experimental studies available in literature on the seismic assessment and retrofit of existing, poorly detailed, reinforced concrete (RC) beam-column joints, typical of pre-1970s construction practice, have concentrated on the two-dimensional (2D) response, using unidirectional cyclic loading testing protocol and constant axial load. Even more limited information is available on the performance of exterior (corner) three-dimensional (3D) RC beam-column joints with substandard detailing subjected to bidirectional loading regime. In this study, the results of a comprehensive experimental program is presented, aiming to show the effects of varying axial and bidirectional loading on the seismic performance of deficient exterior RC beam-column joints before and after retrofit. Ten exterior beam-column joint subassemblies are tested, including four as-built specimens and six retrofitted specimens using externally bonded glass fiber-reinforced polymer (GFRP) sheets. Test results are herein presented...

Modelling exterior beam–column joints for seismic analysis of RC frame structures

AbstractIn common practice, the local response of beam–column joints is not considered for the seismic analysis of multistorey reinforced concrete (RC) frame structures, where these critical regions are typically assumed as rigid. Studies that incorporate the local effect of the joints in the seismic analysis of multistorey RC frame structures are limited. Identifying the main disadvantages of the analytical models that have been proposed so far, a behavioural model is developed for the simulation of the local inelastic response of exterior RC beam–column joints in multistorey RC frame structure. Special attention is given to the description of the main characteristics of the actual seismic response of the joints, including strength and stiffness degradation. The proposed model is incorporated as a rotational spring element in a general program for nonlinear static and dynamic analysis of structures, and a procedure for the evaluation of the required model parameters is also presented. The effectiveness of the proposed joint element model is demonstrated through comparisons with experimental data of 12 RC exterior joints reported in the literature. Moreover, using the proposed element, the influence of the local nonlinear response of RC exterior beam–column joints on the ductility requirements of columns and on the failure mode and overall seismic response of a multistorey RC frame structure is investigated. From the results of these analyses, it is concluded that the modelling of exterior RC joints with reduced capacity as rigid joints can lead to unconservative results and therefore to unsafe design. Copyright © 2008 John Wiley & Sons, Ltd.

Local retrofit of exterior RC beam–column joints using thin RC jackets—An experimental study

AbstractThe use of a new type of reinforced concrete (RC) jacket for RC exterior beam–column connections damaged by seismic excitations is addressed and experimentally investigated. The proposed jacket has very small thickness and includes small diameter steel reinforcement. This jacketing applies at the joint region and at a small part of the columns and the beam. The main advantage of the proposed thin and locally applied jacket compared with the commonly used concrete jacket is the fact that its application is not restrained by space limitations, and since it slightly changes the initial size of the elements, the building's dynamics and seismic behaviour remain practically unaffected. For the needs of this study, 10 exterior beam–column joint subassemblages were constructed and subjected to increasing cyclic loading. Later, the damaged specimens were locally retrofitted using the proposed thin RC jackets and they were retested with the same load sequence. Three different specimen configurations with various amounts of shear reinforcement in the joint area were examined and two types of jackets (a) with light and (b) with dense reinforcement were applied. Test results indicated that the seismic performance of the retrofitted specimens was fully restored and in some cases substantially improved with respect to the performance of the same specimens in the initial loading, since they exhibited higher values of load capacity and hysteretic energy dissipation. Discussion for the conditions of the use of the examined jacketing technique either as a repair or as a strengthening method is also included. Copyright © 2007 John Wiley & Sons, Ltd.

Effectiveness of Reinforcement Details in Exterior Reinforced Concrete Beam-Column Joints for Earthquake Resistance

Effectiveness of Reinforcement Details in Exterior Reinforced Concrete Beam-Column Joints for Earthquake Resistance

Cyclic Response of Exterior Reinforced Concrete Beam-Column Joints Reinforced with Headed Bars—Experimental Investigation

Cyclic Response of Exterior Reinforced Concrete Beam-Column Joints Reinforced with Headed Bars—Experimental Investigation

Analytical Model for Predicting Shear Strengths of Exterior Reinforced Concrete Beam-Column Joints for Seismic Resistance

A softened strut-and-tie model has previously been developed for determining the shear strengths of exterior beam-column joints for seismic resistance. This existing model originates from the strut-andtie concept and satisfies equilibrium, compatibility, and the constitutive laws of cracked reinforced concrete. This paper examines the applicability of the previously proposed model to interior beamcolumn joints. The calculated shear capacities of 56 interior joints were compared with the experimental results, and good agreement was obtained.