• Steel and Composite Structures
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• 제27권1호
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• pp.49-74
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• 2018

Generally, beam-column joints are taken into account as rigid in assessment of seismic performance of reinforced concrete (RC) structures. Experimental and numerical studies have proved that ignoring nonlinearities in the joint core might crucially affect seismic performance of RC structures. On the other hand, to improve seismic behaviour of such structures, several strengthening techniques of beam-column joints have been studied and adopted in practical applications. Among these strengthening techniques, the application of FRP materials has extensively increased, especially in case of exterior RC beam-column joints. In current paper, to simulate the inelastic response in the core of RC beam-column joints strengthened by FRP sheets, a practical joint model has been proposed so that the effect of FRP sheets on characteristics of an RC joint were considered in principal tensile stress-joint rotation relations. To determine these relations, a combination of experimental results and a mechanically-based model has been developed. To verify the proposed model, it was applied to experimental specimens available in the literature. Results revealed that the model could predict inelastic response of as-built and FRP strengthened joints with reasonable precision. The simple analytic procedure and the use of experimentally computed parameters would make the model sufficiently suitable for practical applications.

• 콘크리트학회논문집
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• 제23권3호
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• pp.385-392
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• 2011

이 연구에서는 기존 철근콘크리트 건물의 보-기둥 접합부 및 내진 성능의 개선을 위해 보-기둥 접합부 영역을 기존의 강판 및 FRP보강재(탄소섬유 쉬트, 매입형 탄소섬유봉)를 사용하여 보강한 후 내진 성능을 평가 하였다. 총 6개의 실험체를 제작하고 실험을 수행하여 내진 성능을 평가하였으며, 이 연구의 실험 결과를 근거로 다음과 같은 결론을 얻었다. 기존 철근콘크리트 보-기둥 접합부의 접합부 영역(LBCJ 시리즈)를 보강한 결과 초기 재하시 접합부 영역의 균열 억제 효과와 재하 전 과정을 통하여 보강재의 구속 효과로 인하여 균열 억제 효과가 커서 안정적인 파괴 형태 및 내력 향상 효과를 나타내었다. 기존 철근콘크리트 보-기둥 접합부의 내진 성능을 개선하기 위하여 철근콘크리트 보-기둥 접합부 FRP보강 기술 적용 실험체 LBCJ 시리즈는 표준실험체 LBCJC와 비교하여 최대 내력은 26~50% 증가하였다. 그리고 에너지 소산 능력은 변위 연성 4에서 13.0~14.4% 증가하였다.

• Structural Engineering and Mechanics
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• 제27권4호
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• pp.439-456
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• 2007

Reinforced concrete (RC) joint shear strength models are constructed using an experimental database in conjunction with a Bayesian parameter estimation method. The experimental database consists of RC beam-column connection test subassemblies that maintained proper confinement within the joint panel. All included test subassemblies were subjected to quasi-static cyclic lateral loading and eventually experienced joint shear failure (either in conjunction with or without yielding of beam reinforcement); subassemblies with out-of-plane members and/or eccentricity between the beam(s) and the column are not included in this study. Three types of joint shear strength models are developed. The first model considers all possible influence parameters on joint shear strength. The second model contains those parameters left after a step-wise process that systematically identifies and removes the least important parameters affecting RC joint shear strength. The third model simplifies the second model for convenient application in practical design. All three models are unbiased and show similar levels of scatter. Finally, the improved performance of the simplified model for design is identified by comparison with the current ACI 352R-02 RC joint shear strength model.

• Structural Engineering and Mechanics
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• 제7권4호
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• pp.413-432
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• 1999

A macro-element model is developed to account for shear deformation and bond slip of reinforcement bars in the beam-column joint region of reinforced concrete structures. The joint region is idealized by two springs in series, one representing shear deformation and the other representing bond slip. The softened truss model theory is adopted to establish the shear force-shear deformation relationship and to determine the shear capacity of the joint. A detailed model for the bond slip of the reinforcing bars at the beam-column interface is presented. The proposed macro-element model of the joint is validated using available experimental data on beam-column connections representing exterior joints in ductile and nonductile frames.

• Earthquakes and Structures
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• 제7권5호
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• pp.861-875
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• 2014

This paper studies the response of seismic behavior of reinforced concrete exterior beam-column joints under reversal loading with different anchorages and joint core details. The joint core was detailed without much confinement (group-I) and/or with proposed X-cross bars in the core (group-II). The beam longitudinal reinforcement's anchorages were designed as per ACI 352 (headed bars), ACI 318 (conventional $90^{\circ}$ bent hooks) and IS 456 ($90^{\circ}$ bent hooks with extended tails). The nonlinear finite element analysis response of the beam-column joints was studied, along with initial and progressive cracks up to failure. The experimental and analytical results were compared and presented in this paper to make more scientific conclusions.

• Earthquakes and Structures
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• 제17권4호
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• pp.337-354
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• 2019

This paper presents the results of experimental and numerical studies conducted to investigate the behavior of exterior reinforced concrete beam column joints (BCJ) strengthened by using carbon fiber reinforced polymer (CFRP) sheets. Twelve reinforced concrete beam-column joints (BCJ) were tested in an experimental program by simulating the joints in seismically deficient old buildings. One group of BCJs was designed to fail in flexure at the BCJ interface, and the second group was designed to ensure joint shear failure. One specimen in each set was -retrofitted with CFRP sheet wrapped diagonally around the joint. The specimens were subjected to both monotonic and cyclic loading up to failure. 3D finite element simulation of the BCJs tested in the experimental program was carried out using the software ABAQUS, adopting the damage plasticity model (CDP) for concrete. The experimental results showed that retrofitting of the shear deficient, BCJs by CFRP sheets enhanced the strength and ductility and the failure mode changed from shear failure in the joints to the desired flexural failure in the beam segment. The FE simulation of BCJs showed a good agreement with the experimental results, which indicated that the CDP model could be used to model the problems of the monotonic and cyclic loading of beam-column reinforced concrete joints.

• Structural Engineering and Mechanics
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• 제27권2호
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• pp.223-241
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• 2007

Seven full-scale exterior beam-column joints were produced and tested under reversible cyclic loads to determine. Two of these seven specimens were produced using ordinary reinforced concrete (RC). Steel Fiber Reinforced Concrete (SFRC) was placed in three different regions of the beams of the rest five specimens to determine the extent of the region where SFRC is the most effective. The extent of the region of SFRC was kept constant at the columns of all five specimens. Three of these five specimens which had one stirrup in the joint, were tested to evaluate the effect of the stirrup on the behavior of the beam-column joint together with SFRC. In production of the specimens with SFRC, all special requirements of the Turkish Earthquake Code related to the spacing of hoops were disregarded. Previous researches reported in the literature indicate that the fiber type, the volume content, and the aspect ratio of steel fibers affect the behavior of beam-column joints produced with SFRC. The results of the present investigation show that the behavior of exterior beam-column joints depends on the extent of the region where SFRC is used and the usage of stirrup in the joint, in addition to the parameters listed in the literature.

• 한국지진공학회논문집
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• 제8권2호
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• pp.73-81
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• 2004

본 연구에서는 기존 철근콘크리트건물 보-기둥 접합부의 내진 성능을 개선하기 위하여 탄소섬유를 사용하여 구조물을 보강한 후 실험을 수행하였다. 이를 위하여 6개의 철근콘크리트 보-기둥 접합부를 제작하였으며, 지진하중과 같은 반복하중이 작용할 때 보강재료 및 보강영역 등을 변수로 하여 실험을 수행하여 각 보강변수에 따른 보강효과를 평가하였다. 본 실험을 통하여 구조물의 내진 성능 및 연성능력을 증진시킬 목적으로 새로운 보강재료(탄소섬유판, 탄소섬유봉, 탄소섬유쉬트)로 설계된 보강 실험체(RPC-CP2, RPC-CR, RJC-CP, RJC-CR)들은 내력증진은 물론이고 안정적인 이력거동을 확보할 수 있었다.

• Structural Engineering and Mechanics
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• 제76권3호
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• pp.337-354
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• 2020

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.

• Earthquakes and Structures
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• 제11권5호
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• pp.905-924
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• 2016

Several two-dimensional analytical beam column joint models with varying complexities have been proposed in quantifying joint flexibility during seismic vulnerability assessment of non-ductile reinforced concrete (RC) frames. Notable models are the single component rotational spring element and the super element joint model that can effectively capture the governing inelastic mechanisms under severe ground motions. Even though both models have been extensively calibrated and verified using quasi-static test of joint sub-assemblages, a comparative study of the inelastic seismic responses under nonlinear time history analysis (NTHA) of RC frames has not been thoroughly evaluated. This study employs three hypothetical case study RC frames subjected to increasing ground motion intensities to study their inherent variations. Results indicate that the super element joint model overestimates the transient drift ratio at the first story and becomes highly un-conservative by under-predicting the drift ratios at the roof level when compared to the single-component model and the conventional rigid joint assumption. In addition, between these story levels, a decline in the drift ratios is observed as the story level increased. However, from this limited study, there is no consistent evidence to suggest that care should be taken in selecting either a single or multi component joint model for seismic risk assessment of buildings when a global demand measure such as maximum inter-storey drift is employed in the seismic assessment framework.