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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.
이음된 초고강도 강섬유보강콘크리트 보의 휨강도에 관한 실험적 연구
배백일 ( Baek-il Bae ),손동희 ( Dong-hee Son ),최현기 ( Hyun-ki Choi ),정형석 ( Hyung-suk Jung ),최창식 ( Chang-sik Choi ) 한국구조물진단유지관리공학회 2021 한국구조물진단유지관리공학회 논문집 Vol.25 No.6
본 연구에서는 이음된 초고강도 강섬유보강콘크리트 부재의 휨거동을 검토하고, 현행설계기준의 초고강도 강섬유보강콘크리트 구조물의 이음 설계에 대한 안전성을 평가하기 위해 총 6개의 보에 대한 가력 실험을 수행하였다. 주요 변수는 섬유의 혼입여부와 이음 길이로 설정하였다. 혼입된 섬유는 강섬유로 2%의 부피비로 결정하였으며, 이음길이는 8db와 16db로 결정하여 실험체를 제작하였다. 실험 결과 섬유로 보강되지 않은 실험체들은 이음부에서 급격한 하중지지능력을 상실하고 철근의 항복을 경험하지 못하였으나, 섬유로 보강된 경우 16db의 이음길이가 확보되면 주인장철근의 항복을 경험할 수 있으며, 적절한 휨강도를 발현할 수 있는 것으로 나타났다. 본 연구의 실험결과를 바탕으로 현행설계기준 및 초고강도콘크리트 구조설계지침의 이음길이 산정식들을 검토한 결과 모두 보수적인 평가를 하고 있는 것으로 나타났다. This study examines the bending behavior of lap-spliced ultra-high-strength fiber-reinforced concrete members and evaluates the safety of the design codes for ultra-high-strength fiber-reinforced concrete structures. An experiment on a total of six beams was performed. The main variables were the fiber-inclusion and the lap-spliced length at the center of the beams. The steel fibers in a volume fraction of 2% were used, and the lap-splice lengths were determined to be 8db and 16db. As a result of the test, the specimens not reinforced with fiber lost abrupt load-bearing capacity at the lap region and did not experience yielding of the reinforcing bar. In the case of fiber-reinforced concrete, if a lap-splice length of 16db is secured, the yielding of the main reinforcing bar can be experienced, and appropriate flexural strength can be expressed. Based on the experimental results of this study, as a result of reviewing the lap-splice length calculation formulas of the current design standards and the ultra-high-strength concrete structural design recommendations, it was found that all of them were evaluated conservatively.
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.