겹침이음된 초고강도콘크리트 보의 휨강도에 횡방향보강 요소가 미치는 영향

배백일,최현기 한국구조물진단유지관리공학회 2022 한국구조물진단유지관리공학회 논문집 Vol.26 No.5

In this study, lap spliced ultra-high strength reinforced concrete beams were tested and the code criteria for calculating the lap splice length which was affected by the transverse reinforcement and concrete covering performance were reviewed. The main variables for test were set as fiber volume fraction and transverse reinforcing bar arrangement to improve the confining performance of the concrete cover. The change of the confining performance of concrete cover according to the increase in the fiber mixing amount at 1% and 2% volume ratio was examined, and D10 stirrups with a spacing of 100 mm were placed in the lap spliced region. As a result of the test, the specimens confined by the stirrups showed a sudden drop of load bearing capacity with horizontal cracking at the position of tensile longitudinal reinforcement. However, horizontal cracks were not appeared at the location of longitudinal reinforcement for the specimens with steel fiber. And these specimens showed gradual decrease of load bearing capacity after experiencing peak load. In particular, it was found that the strain at the position of the tensile longitudinal reinforcements of the specimens to which the mixing ratio of 2% was applied exceeds the yield strain. As a result of measuring the strain on the concrete surface, it was found that the fiber was more effective in preventing damage to the concrete surface than the stirrups for short lap spliced region. 본 연구에서는 초고강도 콘크리트에 적용된 겹침 이음의 안전성을 평가하기 위해 초고강도콘크리트 보의 휨성능을 평가하였다. 설계기준에서 정하고 있는 정착 길이 및 겹침이음 길이 산정식에서 겹침이음 길이에 영향을 미치는 횡보강근과 콘크리트 피복 성능의 검토가 수행되었다. 주요 변수는 콘크리트 피복의 구속 성능 증진을 위한 섬유의 혼입과 횡방향철근 배치로 설정하였다. 강섬유가 혼입되었으며 1% 및 2% 부피비로 섬유의 혼입량 증가에 따른 콘크리트 피복 성능의 변화를 검토하였으며, 이음 구간 내에 간격 100mm의 D10 스터럽이 배치되도록 하였다. 실험 결과, 스터럽으로 구속된 실험체는 주인장철근 방향으로의 수평균열 진전과 함께 급격한 하중저하 현상이 나타났으며, 강섬유로 보강된 실험체의 경우 주인장철근 방향의 균열 확대가 억제되고 급작스러운 하중지지능력의 상실을 경험하지 않는 것으로 나타났다. 특히, 2% 의 혼입률이 적용된 실험체의 주인장철근 위치의 변형률은 항복 변형률을 초과하는 것으로 나타났다. 콘크리트 표면에 대한 변형률 측정 결과 철근보다는 섬유가 더 콘크리트 표면의 손상을 방지하는 데에 효과적인 것으로 나타났다.

초고강도 섬유보강 콘크리트 부재의 휨강도 산정

배백일,손종민,최창식,최현기,Bae, Baek-Il,Son, Jong-Min,Choi, Chang-Sik,Choi, Hyun-Ki 대한건축학회 2012 대한건축학회논문집 Vol.28 No.5

In this study, experiments on ultra-high-strength steel fiber reinforced concrete beams with 2% volume fraction of steel fiber had been conducted. Test was conducted by two point loading with 2,000kN actuator for slender beam specimen. Shear-span to depth ratio was 6 intending the flexural failure. For the flexural design of ultra-high strength fiber reinforced concrete member an empirical equation had been proposed. Improving accuracy of empirical equation, 9 possible stress distributions for concrete section was compared with test results. For the reliability of empirical equation, these models were compared with experiment results conducted with previous researches. As a results of comparative study, the most exact solution was the model that use the real stress distribution of ultra-high strength fiber reinforced concrete. However, more safer prediction was possible using stress block parameters that was proposed by the study results of ultra-high strength concrete and tensile stress distribution that was considered the debonding properties of fiber.

전단철근으로 보강되지 않은 강섬유보강 초고강도콘크리트의 전단강도에 대한 실험적 연구

배백일,최현기,최창식 대한건축학회 2017 대한건축학회논문집 Vol.33 No.3

In this study, fiber reinforced ultra high strength concrete beams were tested defining the shear behavior of fiber reinforced ultra high strength concrete and evaluating the previously suggested equations for shear strength of concrete members. The main variables of test are compressive strength of concrete(100, 200 MPa), volume fraction of steel fiber(0, 2%), shear-span to depth ratio(3.4, 2.0). According to the test results, specimens without fiber experienced the abrupt shear failure. In the case of fiber reinforced specimen with shear span ratio of 3.4, failure mode of test specimen is changed into flexural failure. And specimen with shear span ratio 2.0 experienced shear-compression failure mode. However, shear strength increase caused by the increase of compressive strength of concrete is not higher than effect of steel fiber inclusion. In order to make safe design of fiber reinforced ultra high strength concrete under shear, shear strength estimation equations are evaluated. Comparing estimated value with test results, shear strength contribution of matrix is over-estimated and shear strength contribution of steel fiber is under-estimated. Among all equations, equation of AFGC-Setra is most accurate.

초고성능 콘크리트의 압축시 응력-변형률 관계의 특성 분석에 관한 실험적 연구

배백일(Bae, Baek Il),최창식(Choi, Chang Sik),최현기(Choi, Hyun Ki) 한국콘크리트학회 2016 한국콘크리트학회 학술대회 논문집 Vol.28 No.1

초고성능 콘크리트 부재의 연성에 인장강도의 증진이 미치는 영향

배백일(Bae, Baek-Il),최창식(Choi, Chang-Sik),최현기(Choi, Hyun-Ki) 대한건축학회 2014 대한건축학회 학술발표대회 논문집 Vol.34 No.2

초고성능 콘크리트의 압축강도에 기반한 기계적 특성 정의

배백일,최창식,최현기 한국방재학회 2015 한국방재학회 학술발표대회논문집 Vol.14 No.-

최근 초고성능 콘크리트가 RPC의 개념을 상용화하면서 개발되어 사용되고 있다. RPC에 강섬유를 혼입하여 100 MPa 이상의 높은 압축강도를 발현하게 됨에 따라, 급작스러운 취성파괴를 방지할 수 있었으며 높은 수준의 인장강도를 보유할 수 있게 되었다. 그러나, 높은 강도 수준은 현행 설계기준의 적용 시 신뢰성의 확보가 어렵게 됨에 따라 재료의 성능에 기반한 상세설계가 필요하게 된다. 따라서 설계에 적용할 초고성능 콘크리트의 응력-변형률 관계를 정의하기 위한 지표의 추정이 중요하게 된다. 따라서 본 연구에서는 80MPa~200MPa 수준의 압축강도를 보유한 초고성능 콘크리트의 재료 시험을 수행하여 초고성능 콘크리트의 기계적 성능을 검토하였다. 시험 결과 초고성능 콘크리트 또한 보통강도 또는 고강도 콘크리트 영역에서 나타나는 압축강도와 기계적특성 사이의 관계가 불안전측의 추정을 하게 되는 것을 확인할 수 있었다. 이에 기존 연구로부터 수집된, 쪼갬인장강도 원주형 공시체 시험 결과와 프리즘 공시체의 시험결과를 활용하여 기존의 추정식들을 평가하였다. 통계적 평가 결과 시험결과에서 나타난 바와 같이 콘크리트의 압축강도 상승과 함께 낮은 수준의 정확도가 나타나는 것을 확인할 수 있었다. 이에 본 연구에서는 수행된 시험 결과와 수집된 시험 결과들을 사용하여 넓은 압축강도 범위에서 사용 가능한 기계적 성질의 추정식을 도출하였다.

휨-압축을 동시에 받는 섬유보강 분체 콘크리트 압축재의 강도에 대한 연구

배백일(Bae, Baek Il),최현기(Choi, Hyun Ki),최창식(Choi, Chang Sik) 한국콘크리트학회 2011 한국콘크리트학회 학술대회 논문집 Vol.2011 No.5

섬유복합 시트를 통한 조적 벽체의 보강 효과

배백일 ( Bae Bask-il ),박병규 ( Park Byung-kyul ),최현기 ( Choi Hyun-ki ),최창식 ( Choi Chang-sik ) 한국구조물진단유지관리공학회 2010 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.14 No.1

In case of construction of mass concrete structure, there are a lot of possibilities that temperature cracks due to occurred constraint. The hydration heat that was produced in the process of concrete hardening resulted in occurrence of temperature stress on a structure and in some cases. It could cause cracks on a structure and frequently has significant effect on usage and waterproof duration. The occurrence aspect of these temperature cracks can change from how a structure construct. The object of this study is to decide the most suitable thickness which can make a crack be minimized. In this study, therefore, results of hydration heat analysis to a mass concrete structure is compared. Unreinforced masonry buildings have significant portion of existing and historical buildings around the world. Recent earthquakes have shown the needs of seismic retrofitting for these types of buildings. There are many types of retrofitting materials for URM(unreinforced masonry buildings) such as shotcrete, ECC and FRPs. Many engineers use mahy types of fiber reinforced polymers because this types of material enhance the shear strength of wall without expansion of wall sectional area and additional weight of total structure. However, the complexity of mechanical behavior of masonry shear wall and the lack of experimental data of masonry wall which was retrofitted by FRPs may cause the problem that engineers hard to determine the retrofitting level. Determining and providing the information for retrofitting effect of FRPs for masonry shear wall, this paper investigate in-plane shear behavior of URM and retrofitted masonry shear walls using two types of different FRP materials. Specimens were designed to idealize the wall of low rise apartment which was built in 1970s Korea with no seismic reinforcements and have 1 aspect ratio. Three materials were carbon FRP and Hybrid sheet which have different elastic modulus and ultimate strain. Consequently, this study will evaluate the structural capacity of masonry shear wall and retrofitting effect of FRP sheet for in plane shear behavior comparing with evaluation method for reinforced concrete beam which was retrofitted by FRPs.

ECC로 보강한 조적벽체의 전단성능에 관한 실험적 연구

배백일(Bae Baek-Il),박병규(Park Byung-Kyu),최현기(Choi Hyun-Ki),최창식(Choi Chang-Sik) 대한건축학회 2009 대한건축학회 학술발표대회 논문집 - 계획계/구조계 Vol.29 No.1(구조계)

In order to performing remodeling or change the usage of building, URM walls which used commonly in apartment as non-structural element need to have reliable performance of buildings because removal of this types of wall could make more wastes in construction site and removal procedure may cause delay of construction. Using normal shotcrete, as retrofitting method, cannot improve ductility and may cause brittle failure of structure. However, recent study for new materials, such as ECC or UHPC, can solve these problems increasing ductility and toughness of retrofitting materials. In this study, we used sprayed ECCs for retrofitting URM wall. ECCs can be designed to work in conjunction with existing walls to increase both strength and ductility for in-plane behavior of the URM wall. And this may change non-structural masonry wall to structural wall. To ensure that this technique will perform its intended purpose, in-plane lateral loading test was performed. The results of lateral load test of two retrofitted URM compared to non-retrofitted one. Retrofitted walls are consisted of just sprayed and anchored to wall base, RTM-ECC and have wiremesh, same detail of others, RTM-ECC-WM. Retrofitted specimens show significant increase of strength, ductility and energy dissipation capacity compared to URM. RTM-ECC show stiff strength degradation however, RTM-ECC-WM show slow degradation of strength because of the load transferring effect of wiremesh.

개구부 형태에 따른 전단벽의 거동특성

배백일(Bae, Baek Il),이관호(Lee, Kwan Ho),최현기(Choi, Hyun Ki),최윤철(Choi, Yun Choul),최창식(Choi, Chang Sik) 한국콘크리트학회 2007 한국콘크리트학회 학술대회 논문집 Vol.2007 No.11