• 대한건축학회논문집:구조계
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• 제34권11호
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• pp.19-26
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• 2018

This paper presents the shear strengthening effect of externally post-tensioning (EPT) method using high-strength steel rod in pre-cracked reinforced concrete (RC) beams. Three- and four-point bending tests were performed on a total of 8 specimens by adjusting the strengthening depths in the deviator position of EPT. The effective strengthening depths were 435, 535, and 610 mm. The pre-loading up to about 2/3 of ultimate load capacity measured in unstrengthened RC beam were applied in the beam to be post-tensioned. The EPT method was then applied to the pre-damaged RC beams and re-loading was added until the end of the test. EPT restored deflections of 3 mm or more, which account for about 40% of deflection when the pre-loading was applied. The shear strengthening increases more than 3 times and 36~107% in terms of the stiffness and load-carrying capacity compared to unstrengthening RC beams. The increased load-carrying capacities of the post-tensioned beam with strengthening depths of 435 and 535 mm are almost the same as 36~61%, and those of 610 mm are 84~107%, which shows the greatest shear strengthening effect.

• 대한건축학회논문집:구조계
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• 제35권10호
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• pp.181-190
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• 2019

In this study, four reinforced concrete coupling beams were subjected to cyclic lateral loading test to evaluate the structural performance of coupling beam according to volume fraction of steel fiber. For this purpose, the volume fraction of steel fiber(0%, 1%, 2%) and transverse reinforcement spacing were determined as the main parameter. According to the test results, the maximum strength of D-40C-s100-0 was 1.15, 1.13, 1.05 times higher than D-40C-s300-0, D-40C-s300-1, D-40C-s300-2, respectively. The maximum strength of coupling beams with mitigated rebar details increases as the volume fraction of steel fiber increases. Although steel fiber 2% reinforced specimen(D-40C-s300-2) did not satisfy the amount of transverse reinforcement required for seismic design of coupling beam, the overall performance including to maximum strength, ductility and energy dissipation capacity was similar to the control specimen(D-40C-s100-0). As a result, the use of steel fiber with 2% reinforcement can partially replace the transverse reinforcement in diagonally reinforced concrete coupling beam.

• 한국공간구조학회논문집
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• 제21권1호
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• pp.71-78
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• 2021

The U-flanged truss hybrid beam is a new composite beam made by pouring concrete into the U-flanged truss beam. In this study, an experimental study was performed to verify the shear capacity of U-flanged truss hybrid beams with the newly developed end reinforcement details. For all specimens, the maximum shear strength was determined by shear failure of concrete in the loading point The detail reinforced with stirrups at the end zone can exhibit the greatest shear strength, but the method of reinforcing the end zone using vertical steel plates, which is a relatively easy method to manufacture, is considered to be the most effective detail in terms of shear strength and ductility. Also, in the case of U-flanged truss hybrid beams reinforced with vertical steel plates at the end zone, the shear strength can be evaluated on the safety side by using the Korea Design Standard formula.

• Steel and Composite Structures
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• 제45권1호
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• pp.101-118
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• 2022

The seismic performance of the reinforced concrete (RC) special-shaped column to steel beam connections with steel jacket used in the RC column to steel beam fabricated frame structures was investigated in this study. The three full-scale specimens were subjected to cyclic loading. The failure mode, ultimate bearing capacity, shear strength capacity, stiffness degradation, energy dissipation capacity, and strain distribution of the specimens were studied by varying the steel jacket thickness parameters. Test results indicate that the RC special-shaped column to steel beam connection with steel jacket is reliable and has excellent seismic performance. The hysteresis curve is full and has excellent energy dissipation capacity. The thickness of the steel jacket is an important parameter affecting the seismic performance of the proposed connections, and the shear strength capacity, ductility, and initial stiffness of the specimens improve with the increase in the thickness of the steel jacket. The calculation formula for the shear strength capacity of RC special-shaped column to steel beam connections with steel jacket is proposed on the basis of the experimental results and numerical simulation analysis. The theoretical values of the formula are in good agreement with the experimental values.

• 한국강구조학회 논문집
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• 제29권2호
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• pp.135-145
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• 2017

본 연구는 춤이 큰 하이브리드 합성보의 1차 휨 성능 평가 후, 2차 연구로써 춤이 큰 하이브리드 합성보와 기둥 접합부의 내진성능평가 실험이다. 실험 변수는 보 춤, 부모멘트 철근 수, 브라켓과 보 이음부의 볼트 수 등으로 3개의 실험체를 제작하였다. 접합부 상세는 기둥에 브라켓을 접합 후, 브라켓에 하이브리드 보를 이음하였다. 브라켓과 보 이음은 하부와 웨브는 볼트접합, 상부는 용접접합하였다. 실험결과 내력은 정 부모멘트 모두 소성모멘트($M_p$) 이상을 확보하였으며, 변형능력은 3% 이상의 층간변위각을 확보하여 합성중간모멘트골조의 요구조건을 만족하는 것으로 나타났다. 그러므로 춤이 큰 하이브리드 합성보에 철골철근콘크리트 기둥을 적용하는 경우 본 연구결과의 접합부상세를 적용하면, 중간모멘트골조의 내진성능을 확보할 수 있다고 판단된다.

• 콘크리트학회논문집
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• 제29권2호
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• pp.201-208
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• 2017

외부 보-기둥 접합부에서는 철근정착을 위해 갈고리철근 사용하고 있으며, 철근과밀배근 해소와 시공작업의 어려움으로 확대머리철근의 사용이 증가하고 있다. SD600 51 mm 확대머리철근을 사용할 경우 ACI318-14 및 KCI2012기준에서 사용을 제한하고 있다. 이번 연구에서는 외부 보-기둥 접합부 내에 고강도 대구경 철근의 확대머리 철근의 사용이 가능하도록 실험 60 MPa, 80 MPa 콘크리트강도로 제작된 실험체의 정착상세별 구조성능을 평가하였다. 모든 실험체에서는 보의 휨항복파괴가 발생하였으며, 실험체의 모멘트-변위 곡선에서 비슷한 양상을 보였다. 다른 실험체보다 갈고리가 한쪽방향으로 배근한 실험체에서는 갈고리철근 배근방향에 의해 전단저항능력이 달라지므로 3.5%변위비 이후에 부착응력 감소가 더 크게 나타났으며, 전단변형능력도 더 크게 나타났다. 실험체의 내진성능을 확인하기 위하여 ACI374.1-05기준과 비교하였으며, 실험결과 충분한 내진성능을 확보하였다. 이를 통하여 외부 보-기둥 접합부에서 SD600, 51 mm 확대머리철근의 사용이 가능한 것으로 판단된다.

• Computers and Concrete
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• 제19권4호
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• pp.405-411
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• 2017

Carbon Fiber Reinforced Plastic (CFRP) has commonly been used to strengthen existing RC structures. Wrapping the whole component with CFRP is an effective method and simple to execute. Besides, specific configuration of CFRP sheets (L, X and T shape) has also been considered in some experiments to examine CFRP effects in advance. This study aimed to provide an optimal CFRP configuration to effectively retrofit the beam-column connection using continuous material topology optimization procedure. In addition, Moved and Regularized Heaviside Functions and penalization factors were also considered. Furthermore, a multi-material procedure was also used to compare with the results from the single material procedure.

• 한국지진공학회논문집
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• 제24권4호
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• pp.189-196
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• 2020

In this study, two full-scale gravity load-designed reinforced concrete corner beam-column joints were tested by being subjected to uniand bi-directional cyclic lateral loading. The test variable was loading type: uni- or bi-directional loading. To investigate the effect of the loading type on the cyclic behavior of joint specimens, damage progression, force-deformation relation, contribution of joint deformation to total drift, joint stress-strain response, and cumulative energy dissipation were investigated. The test data suggest that bidirectional loading can amplify damage accumulation in the joint region.

• 한국지진공학회논문집
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• 제20권2호
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• pp.91-101
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• 2016

This study is the compared seismic performance that are difference between the performance of structures on various site classes and beam-column connection. this analysis model was designed the previous earthquake load. To compare the performance levels of the structure was subjected to nonlinear static and nonlinear dynamic analysis. Nonlinear analysis was used to The Perform 3D program. Nonlinear static analysis was compared with the performance point and Nonlinear dynamic analysis was compared the drift ratio(%). Analysis results, the soft site class of the displacement was more increase than rock site classes of the displacement. Also The smaller the displacement was increased beam-column connection stiffness.

• 한국지진공학회논문집
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• 제20권6호
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• pp.361-368
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• 2016

Coupling beams serve as primary source of energy dissipation in coupled shear wall systems during large earthquakes. However, the overestimation of the shear strength of diagonally reinforced coupling beams may be adverse effect on the seismic performance of coupled shear wall systems. In order to force coupling beams to properly work during earthquakes, coupling beams should be designed with accurate shear strength equations. The objective of this study is to propose the accurate shear strength equation for slender diagonally reinforced coupling beams. For this purpose, experimental tests were conducted using three diagonally reinforced coupling specimens with different amount of transverse reinforcement under reversed cyclic loads to evaluate the hysteretic behavior of the specimens. The test results show that transverse reinforcement of slender diagonally reinforced coupling beam affects the maximum strength and drift ratio.