• Journal of the Korea Concrete Institute
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• v.24 no.4
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• pp.399-406
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• 2012

Beam-column joints are generally recognized as the critical regions in the moment resisting reinforced concrete (RC) frames subjected to both lateral and vertical loads. As a result of severe lateral load such as seismic loading, the joint region is subjected to horizontal and vertical shear forces whose magnitudes are many times higher than in column and adjacent beam. Consequently, much larger bond and shear stresses are required to sustain these magnified forces. The critical deterioration of potential shear strength in the joint area should not occur until ductile capacity of adjacent beams reach the design demand. In this study, a method was provided to predict the deformability of reinforced concrete beam-column joints failing in shear after the plastic hinges developed at both ends of the adjacent beams. In order to verify the deformability estimated by the proposed method, an experimental study consisting of three joint specimens with varying tensile reinforcement ratios was carried out. The result between the observed and predicted behavior of the joints showed reasonably good agreement.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.40 no.4
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• pp.363-370
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• 2020

This paper reports the results of an experimental study using the BOTDR sensor to detect the unbonded location of attached CFRP sheet for structural rehabilitation. A specimens with the unattached CFRP sheet were fabricated for this study, on which BOTDR sensor was attached with a nylon net. During the flexural test of the specimens, the strain of the CFRP sheet was measured using the BOTDR sensor and electric resistance gauges. From the results, it was confirmed that the strain distribution obtained through the BOTDR sensor can be effectively used to visualize and detect the unbonded position of the CFRP sheet. In addition, In addition, the strain measured by the BOTDR sensor was found to be more effective in analyzing the overall structure behavior than the electric resistance strain gauge. The development of a BOTDR sensor with a measuring longth of less than 100 mm will enable accurate detection of the local unbonded position of the CFRP sheet.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.1
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• pp.39-48
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• 2015

Reinforced concrete (RC) structures strengthened with FRP materials would cause the loss of the reinforcing effect and the sudden failure of the structure due to the debonding of FRP. The debonding fracture strength of the FRP-strengthened concrete structures has been evaluated using the same strength method as applied in RC structures based on the debonding strain of FRP. However, the values of the FRP debonding strain are different according to design guidelines. Thus, this study carried out an experimental study on RC beams reinforced with GFRP and evaluated the debonding fracture strength of the strengthened beams from each design guideline. Since the debonding failure occurs prior to reaching the ultimate value of concrete compressive strain, this study accounts for the nonlinear stress distribution of concrete. This study also proposed equations that can evaluate the debonding strength of GFRP-strengthened RC beams with similar safety to the ultimate flexural strength of non-strengthened RC beams.

• Journal of the Korea Concrete Institute
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• v.13 no.3
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• pp.251-260
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• 2001

It is required to evaluate the axial strain of reinforced concrete beams in order to predict the ductility of reinforced concrete beams subjected to reversed cyclic loading. A model was proposed to determine the axial strains In reinforced concrete beams by analysing the behavior of reinforced concrete sections and comparing with published test results. The proposed axial strain model inclusively reflected four kinds of paths : Path 1-steel bar in an elastic stage or a unloading region; Path 2-after flexural yielding; Path 3-a slip region; and Path 4-a reversing loading region. The equations to predict the axial strains of each path were proposed. The proposed equations took into account the effects of the loading program. Comparison of axial strains between experimental results and the results from proposed equations showed to be in a good agreement with experimental results.

• Journal of the Korea Concrete Institute
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• v.22 no.6
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• pp.833-841
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• 2010

In this report, the test results of five reinforced concrete beam-column joint subjected to cyclic load are presented. The main purpose of the research is to investigate the influence of the steel pull-out of the beam-column joints to the shear and ductile capacity of the RC beam-column assembles. In addition, the influence of the amount of beam reinforcement to the joint shear and ductile capacity is evaluated. Test results indicate that the yield penetration of steel bar increases as the joint shear strength ratio, $V_{j1}/V_{jby}$ decreases. And the slippage of the steel bars are varied according to the region of the beam-column joints. The pull-out of the steel bars of five specimens was almost the same regardless of the joint shear strength ratio, $V_{j1}/V_{jby}$. Because it was affected by not only the yield penetration of steel bar but also the axial elongation in the plastic hinge.

• Journal of the Korea Concrete Institute
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• v.18 no.3 s.93
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• pp.379-388
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• 2006

This paper presents a model for evaluating the contribution by arch action to shear resistance in shear-critical reinforced concrete beams. Based on the relationship between shear and bending moment in beams subjected to combined shear and bending, the behavior of a beam is explicitly divided into two base components of the flexural action and the tied arch action. The compatibility condition of the shear deformation that deviates from Bernoulli bending plane is formulated utilizing the smeared truss idealization with an inclined compression chord. The Modified Compression Filed Theory is employed to calculate the shear deformation of the web, and the relative axial displacements of the compression and the tension chord by the shear flow are also calculated. From this shear compatibility condition in a beam, the shear contribution by the arch action is numerically decoupled. Then the validity of the model is examined by applying the model to some selected test beams in literatures. The results may confirm the rationale of the proposed behavioral model.

• Journal of the Korea Concrete Institute
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• v.13 no.2
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• pp.130-138
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• 2001

This paper presents on the shear behavior prediction of reinforced concrete beams using Transformation Angle Truss Model (TATM). The TATM can evaluate the stress-strain relationships for cracked concrete by transforming stresses and strains for principal plane into those over the crack surfaces. This proposed analytical method simplifies the Fixed Angle Softened Truss Model (FA-STM) and removes the limitation of applicability of the FA-STM. The shear.strength and strain of reinforced concrete beams are predicted by using the TATM. For the verification of proposed method, experimental results of reinforced concrete beams were compared with theoretical results by the TATM, FA-STM and Rotating Angle Softened Truss Model (RA-STM).

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.5
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• pp.911-920
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• 1989

It this study, beam-type bend specimen is used to evaluate the interlaminar fracture toughness of laminated composite under mixed-mode deformations. The specimen is loaded under three-point bending and hence produced mixed-mode deformations in the vicinity of the crack tip according to the variation of the thickness ratio on delamination plane. Total energy release rate is obtained by elementary beam theory considering the effect of shear deformation. The partitioning of total value into mode-I and mode-II components is also performed. The mixed-mode interlaminar fracture toughness is evaluated by experiments on specimens with several thickness ratios of delamination plane. As the part of delamination plane is thicker, the effect of shear deformation on total energy release rate is increased. Beam-type bend specimen men may be applied to obtain informations on the mixed-mode interlaminar fracture behavior of laminated composites.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.6
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• pp.193-203
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• 2022

In this study, in order to compare the seismic performance of steel structure beam-column connection details and non-scallop connection details mainly used in Korea, a full-scale static cyclic loading test and FEM analysis were conducted through the same modeling as the experiment. For quantitative numerical comparison, the strain concentration ratio and moment transfer efficiency used in previous studies were cited. As the welding area of the beam web decreased, the deformation rate of the beam flange increased, and the plastic deformation capacity according to the rotation angle decreased or brittle fracture occurred. Comparing the analysis results with the experimental results, the possibility of brittle fracture tended to increase when the web welding ratio for the total cross-sectional area of H-shaped fell below 60%.

• Proceedings of the Korean Fiber Society Conference
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• 2002.04a
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• pp.57-61
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• 2002

점탄성학은 고분자물과 같이 기계적 성질이 시간에 따라 변하는 물질의 응력과 변형해석에 관한 학문이다. 이에 대한 이전의 문헌들은 균일변형시의 조성식에 대한 주제를 주로 다룬 반면, 경계조건 문제(boundary value problem)로서의 불균일 변형해석에 대한 논의가 부족한 편이다. 본 논문에서는 불균일 변형해석에 유용한 상응원리 (correspondence theorem)[1]을 보이론(beam theory)에 적용하는 경우, 적용가능조건을 유도하는 한편 상응원리를 적용 예를 들어 설명하였다. (중략)