Exterior Beam-column Joints Research Articles

Performance Evaluation of Exterior Beam–Column Joint with Core Reinforcement Technique Subjected to Reverse Cyclic Loading

The present work aims to study the performance of exterior beam–column joint with core reinforcement technique subjected to reverse cyclic loading. In this experimental study, three sets of one-third scaled exterior beam–column joint specimens using M30 grade concrete were cast and tested. The first set of specimens were detailed as ordinary moment resisting frame (IS:456 and SP:34) and designated as joint BCJ1. The second sets of specimens were detailed as special moment resisting frame (IS:13920) and designated as joint BCJ2. In the third set, the reinforcement detailing followed in joint BCJ1 was integrated with a new type of reinforcement (called “core reinforcement”) proposed in this study and designated as joint BCJ3. Based on the experimental result, the joint BCJ3 gave the better performance considering the strength in terms of load-carrying capacity, energy dissipation capacity, stiffness and ductility factor. The results of reverse cyclic loading tests performed in the exterior beam–column joint models indicate that the additional core reinforcement in the beam–column joint region provide adequate ductility. The stiffness of the joint with additional core reinforcement in the beam–column joint region did not undergo much reduction when compared to other types of joints. In addition, the usage of core reinforcement in the joint region can reduce its installation and difficulties in placing and compacting the concrete. This combination of core reinforcement technique in the beam–column joint region may contribute to reduction in destruction due to earthquakes.

Seismic performance of reinforced concrete building exterior joints with substandard details

Beam-column joints are important components of the seismic-force-resisting system in reinforced concrete (RC) frame buildings. A majority of older buildings have serious structural deficiencies and are substandard according to current seismic design criteria. Failure of beam-column joints with substandard details has caused building collapse during strong earthquakes. This paper evaluates the seismic performance of exterior beam-column joints with three different details of beam reinforcement; no transverse reinforcement was used in the beam-column joints. A total of six RC exterior joints with substandard details were tested under quasi-static cyclic loads and their performance was examined in terms of plastic rotation, joint shear strength and strain, and residual strength. Two levels of column axial compression were investigated and the influence of the axial load level on the performance of the joints is evaluated; in addition, the bond-slip behavior of the bottom beam bars is discussed. Joint shear failure and bond-slip failure were observed. The joint shear strength of the tested subassemblies exceeded the performance criteria stated in ASCE 41 for all test units with joint shear failure; however, joint shear strength was found to be lower than the requirements for Type 2 joints per ACI 352.

Influence of Fiber Reinforced Concrete on Plastic Behavior on Exterior Beam Column Joint under Cyclic Loading

The plastic behavior of exterior beam-column joint with different fiber reinforced concrete (FRC) is explored experimentally under cyclic loading. Steel fiber and polypropylene fibers are used in fiber reinforced concrete and engineered cementitious composites respectively. A total of four specimens were prepared, among the four two specimens are conventional and remaining two are with different FRC. The hysteresis loop, stiffness degradation, energy dissipation and damage index are the considered parameters to quantify the plastic response of employed technique. The quantification of results shows enhanced load carrying capacity and energy dissipation capacity with lesser rate of stiffness degradation. The post failure analysis authenticates that the use of fiber improves the damage tolerance behavior and ductility enhancement without sudden loss in strength.

Experimental Study on Structural Performance of RC Exterior Beam-Column Joints Retrofitted by Steel Jacketing and Haunch Element under Cyclic Loading Simulating Earthquake Excitation

Several retrofitting methods for reinforced concrete (RC) beam-column joints in old buildings without seismic details were developed. Four half-scale RC exterior beam-column joints were fabricated and tested under cyclic loading simulating earthquake excitation. The control specimen was designed to fail in joint shear. Two practical retrofitting strategies were applied to the control specimen which consider the architectural characteristic in real buildings, including steel jacketing and haunch retrofit solution. The structural performance of the test specimens was investigated in terms of various factors including damage and failure, load-drift relationship, ductility, dissipated energy, and strain profiles of longitudinal reinforcement. Experimental results confirmed that the proposed retrofit methods were shown to enhance the seismic capacity of the joints in terms of the strength, deformation capacity, and energy dissipation capacity while the shear deformation in the panel zone significantly reduced in comparison with the control specimen.

The Hysteretic Behavior of Partially Pre-Stressed Beam-Column Joint Sub-assemblages Made of Reactive Powder Concrete

Reactive powder concrete (RPC) is an alternative to normal concrete (NC) allowing for significantly higher strength of partially pre-stressed concrete structures. In the Indonesian national standard SNI 03-2847-2013 (2013) and the American standard ACI 318-14 (2014), the partial pre-stressed ratio (PPR) is limited to a maximum of 25.0 percent to ensure that pre-stressed concrete structures remain ductile and capable to dissipate seismic energy sufficiently. The objective of this experimental study was to investigate the hysteretic performance of partially pre-stressed-RPC (PP-RPC) for both interior and exterior beam-column joint sub-assemblages. Four specimens with different levels of PPR were tested with a combination of constant axial compression and cyclic lateral loads. The PPR used for the first and the second two specimens were 22.8% and 33.8%, respectively. The strength of the RPC was 101.60 MPa for all specimens. The results showed that increasing the PPR of PP-RPC improves its hysteretic performance. The best performing specimen, with a PPR of 33.8%, had a ductility that was 1.97 times that of the specimen with a PPR of 22.8%.

Headed bars in simulated exterior beam-column joints of Ultra-high-performance fiber-reinforced concrete

Headed bars in simulated exterior beam-column joints of Ultra-high-performance fiber-reinforced concrete

Stud reinforcement in beam-column joints under seismic loads

Current codes recommend large amounts of shear reinforcement for reinforced concrete beam-column joints that causes significant bar congestion. Increase in congestion of shear reinforcement in joint core (connection zone), leads to increase accomplishment problems. The congestion may also lead to diameter limitations on the beam bars relative to the joint dimensions. Using double headed studs instead of conventional closed hoops in reinforced concrete beam-column joints reduces congestion and ensures easier assembly of the reinforcing cage. The purpose of this research is evaluating the efficiency of the proposed reinforcement. In this way, 10 groups of exterior beam-column joints are modeled. Each group includes 7 specimens by different reinforcing details in their joint core. All specimens are modeled by using of ABAQUS and analyzed subjected to cyclic loading. After verification of analytical modeling with an experimental specimen, 3D nonlinear specimens are modeled and analyzed. Then, the effect of amount and arrangement of headed studs on ductility, performance, ultimate strength and energy absorption has been studied. Based on the results, all joints reinforced with double headed studs represent better performance compared with the joints without shear transverse reinforcement in joints core. The behavior of the former is close to joints reinforced with closed hoops and cross ties according to the seismic design codes. By adjusting the arrangement of double-headed studs, the decrease in ductility, performance, ultimate moment resistant and energy absorption reduce to 2.61%, 0.90%, 0.90% and 1.66% respectively compared with the joints reinforced by closed hoops on the average. Since the use of headed studs reduces accomplishment problems, these amounts are negligible. Therefore, use of double-headed studs has proved to be a viable option for reinforcing exterior beam-column joints.

Seismic Performance Evaluation and Strengthening of RC Frames with Substandard Beam-Column Joint: Lessons Learned from the 2013 Bohol Earthquake

On October 15, 2013, a magnitude 7.1 earthquake severely damaged buildings on Bohol Island, the Philippines. This paper briefly reports on the typical damage to reinforced concrete (RC) buildings observed in the authors’ post-earthquake investigation. The current study focuses on the seismic performance of an earthquake-damaged building with exterior beam-column joint failure. Cyclic loading tests were conducted to propose a practical seismic strengthening method by installing RC wing walls for substandard moment-resisting frames with brittle beam-column joints. A scaled model representing the earthquake-damaged frame reproduced the damage to the exterior beam-column joint, which could not be evaluated using Japanese seismic evaluation methods because of an overestimation of the joint performance. Another specimen strengthened by the proposed method was successfully upgraded, forming a ductile beam yielding mechanism. The ultimate strength of the upgraded specimen estimated by the Japanese methods agreed well with the experimental results. The strengthening mechanism by wing walls was elucidated, knowledge of which will be useful for future applications to substandard buildings in developing countries.

EFFECT OF USING HIGHLY CONFINED SHORT LAP-SPLICE REINFORCEMENT ON SEISMIC PERFORMANCE OF EXTERIOR BEAM-COLUMN JOINT

The present paper aims to examine the behavior of exterior beam-column joints with different reinforcement details of their columns: continuous and lap splice longitudinal bars were adopted as design parameter. The experimental program was carried out at the Concrete Research Laboratory at Housing and Building Research Center in Egypt; included three exterior reinforced beam column joints that were tested under the effect of quasi-static cyclic loading. One sample was designed according to the provisions of the current seismic design codes and served as a control sample. Columns of the other two samples were detailed with well confined shorter lap spliced longitudinal reinforcement. The overall behavior of the beam-column joints and conclusions are discussed in this paper.

Parametrical study of the behavior of exterior unreinforced concrete beam-column joints through numerical modeling

Exterior beam-column joints are structural elements that ensure connection between beams and columns. The joint strength is generally assumed to be governed by the structural element of lowest load capacity (beam or column), however, the joint may be the weakest link. The joint shear behavior is still not well understood due to the influence of several variables, such as geometry of the connection, stress level in the column, concrete strength and longitudinal beam reinforcement. A parametrical study based only on experiments would be impracticable and not necessarily exposes the failure mechanisms. This paper reports on a set of numerical simulations conducted in DIANA<TEX>$^{(R)}$</TEX> software for the investigation of the shear strength of exterior joints. The geometry of the joints and stress level on the column are the variables evaluated. Results have led to empirical expressions that provide the shear strength of unreinforced exterior beam-column joints.

NUMERICALLY SIMULATING THE EFFECT OF REBAR DISTRIBUTION ON THE CONCRETE FLEXURAL STRENGTH

Abstract This paper presents a developed three dimensional (3D) finite element (FE) model, using ABAQUS software, to explore the effect of the reinforcing rebar distribution on the flexural strength for exterior beam-column joints. The results of the experimental tests conducted by Rekha S. P. et al. [1], are used to validate the results of the developed FE model. Three exterior beam-column joint specimens, have been experimentally investigated under the effect of static loading by Rekha S. P. et al. [1]. Each of the tested specimen has the same reinforcement ratio but with varying bar diameters to allow for variable distribution of reinforcing rebar. Three more beam-column joint specimens have been prepared exactly as the first three specimens but with beam of closer stirrups spacing. The six specimens have been statically loaded reaching the failure load and hence the flexural strength was determined for each. Six FE models of exterior beam-column joint are created simulating the former experimentally tested concrete joints. The developed geometrically and material nonlinear 3D model is able to trace the load-displacement path for all the tested concrete joints with adequate accuracy.

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.

Experimental tests of unreinforced exterior beam–column joints with plain bars

Reinforced concrete buildings designed according to obsolete seismic codes or for gravity loads only are widespread in Italian and Mediterranean building stock. Past earthquakes showed that, for these buildings, shear failure in beam–column joints can lead to structural collapse mainly due to the inadequate joint confinement. The construction details used in these structural elements are commonly recognized as the likely cause of non-ductile structural failure modes under seismic actions, due to the lack of capacity design principles.A significant amount of research on seismic performance of unreinforced beam–column joints has been carried out in last years, but a very few portion of them handled with specimens unreinforced in the joint region and with plain hook-ended longitudinal bars. A higher number of tests is needed to deeper understand joint seismic response in order to validate the (few) existing models or calibrate new ones.This study aims at improving the understanding of seismic performance of exterior non-conforming joints in existing RC buildings. Two experimental tests on joints without transverse reinforcement are designed and carried out. The specimens are different for beam longitudinal reinforcement ratio and they are both reinforced with plain longitudinal bars. Two different kinds of joint failure are expected, with or without yielding of the adjacent beam. Design criteria, adopted setup and main experimental results are described. Strain gauges located on beam bars and displacement transducers on the joint panel allow the complete definition of both the deformability contributions of fixed-end-rotation and shear strain of joint panel. Finally, a comparison between joint shear strength models existing in literature or codes and experimental results (considering a wider experimental database) is carried out.

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.

Experimental investigation on the seismic anchorage behavior of headed bars based on full-size specimens of exterior and interior beam–column joints

The design of headed bars in interior and exterior beam–column joints to ensure satisfactory seismic anchorage performance has recently become a very important issue. This work investigates the seismic anchorage behavior of headed bars using 12 groups of full-size specimens of exterior and interior beam–column joints and suggests design requirements for headed bars in such joints. On the basis of the experimental investigation, this work comprehended the seismic anchorage behavior of headed bars using full-size specimens of exterior and interior beam–column joints and suggested design requirements for headed bars in such joints. Additionally, the application of headed bars with spliced and butted types on interior beam–column joints is also proved in this work. Therefore, based on the experimental results, the minimal required net spacing of headed bars can be set at 2.2 db, instead of 4.0 db, for seismic designs, and the minimal required anchorage length in ACI 318-11 for non-seismic design members can be used in seismic members.

Experimental assessment of unreinforced exterior beam–column joints with deformed bars

In the performance assessment of typical existing buildings, seismic collapse safety might be significantly affected by non-linear behavior of joints that are involved in the failure mechanism, especially if they are characterized by poor structural detailing such as the lack of an adequate transverse reinforcement in the joint panel.Unfortunately, commonly accepted tools to assess existing joints capacity are not available. Few reliable approaches for modeling all sources of nonlinearity are proposed in literature for poorly designed beam–column joints because of relatively poor information from experimental tests.The present study aims at improving the understanding of seismic performance of exterior joints without transverse reinforcement in existing RC buildings through experimental tests.Two full-scale exterior unreinforced beam–column joint sub-assemblages are tested under cyclic loading. The specimens are reinforced with deformed bars but they are different for beam longitudinal reinforcement ratio. Two different kinds of joint failure are expected, with or without the yielding of the adjacent beam. Strain gauges located on beam bars and displacement transducers on the joint panel allow the complete definition of both the main deformability contributions, namely fixed-end-rotation and shear strain of joint panel, highlighting the differences between failure modes.Design criteria, adopted setup and experimental results are described and discussed. Finally, experimental results are compared with proposals from literature in terms of shear strength.

Structural performance of reinforced concrete exterior beam–column joint subjected to combined shear and torsion

This article presents the results of an experimental study conducted in order to investigate the behavior of Type-I beam–column joints, where the beam was subjected to shear stresses due to combined effect of shear force and torsional moment (beam eccentric loading). Eight beam–column joint specimens were constructed and tested up to failure in order to better understand the complicated behavior due to combined loading transmitted from the beam to the column. The studied parameters were the eccentricity of beam load (torsional-moment-to-shear-force ratio Mt/ Q), the configuration of beam side and compression reinforcing steel, the existence of the joint reinforcing stirrups, and the beam rigidity. Generally, the shear failure at the beam zone or at the joint panel was noticed to be the governing mode of failure for all tested specimens. The test results highlighted the importance of the configuration of both longitudinal side and compression reinforcing steel of the beam, where the inadequate embedded length of both of them into the joint panel including stirrups decreased the beam ultimate capacity but it kept the failure zone away from the joint panel. Finally, a three-dimensional truss model was presented and analyzed. The results of the three-dimensional model showed good agreement with the experimental findings.

Structural behavior of RC engineered cementitious composite (ECC) exterior beam–column joints under reversed cyclic loading

This paper investigates the effects of engineered cementitious composite (ECC) on the behavior of RC exterior beam–column joint under reversed cyclic loading. The main parameters considered include the load–deflection relationship, crack propagation, moment–rotation relationship at the joint, and energy absorption capacity. The experimental work was conducted on a normal concrete and an ECC full scale RC exterior beam–column joint. The specimen was subjected to reverse cyclic loading under controlled deformation at the tip of the beam until failure. At post cracking stages, the ECC joint showed significant improvement in the ultimate shear and moment capacities, as well as in the deformation behavior and damage tolerance, compared with the NC specimen at ultimate and failure stages. Numerous tiny cracks with reduced crack width and spacing forming a dense of network propagated within the joint region.

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.

Finite Element Analysis (FEA) for the Beam-Column Joint Subjected to Cyclic Loading Was Performed Using ANSYS

This paper analyses the seismic performance of exterior beam-column joints strengthened with unconventional reinforcement detailing. The beam-column joint specimens were tested with reverse cyclic loading applied at the beam end. The samples were divided into two groups based on the joint reinforcement detailing. The first group (Group A) of three non-ductility specimens had joint detailing in accordance with the construction code of practice in India IS456-2000, and the second group (Group B) of three ductility specimens had joint reinforcement detailed as per IS13920-1993, with similar axial load cases as the first group. The experimental studies are proven with the analytical studies carried out by finite element models using ANSYS. The results show that the hysteresis simulation is satisfactory for both un-strengthened and ferrocement strengthened specimens. Furthermore, when ferrocement strengthening is employed, the strengthened beam-column joints exhibit better structural performance than the un-strengthened specimens of about 31.56% and 38.98 for DD-T1 and DD-T2 respectively. The analytical shear strength predictions were in line with the test results reported in the literature, thus adding confidence to the validity of the proposed models.