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보강섬유 종류에 따른 변형경화형 시멘트 복합체의 거동특성
윤현도(Yun Hyun-Do),김용철(Kim Yong-Cheol),김선우(Kim Sun-Woo) 대한건축학회 2008 大韓建築學會論文集 : 構造系 Vol.24 No.5
Fiber is an important ingredient in strain-hardening cementitious composite (SHCC), which can control fracture of cementitious composite by bridging action. The properties of reinforcing fiber, as tensile strength, aspect ratio and elastic modulus, have great effect on the fracture behavior of SHCC. Therefore, a variety of experiments have being performed to access the performance of SHCC recently. The research emphasis is on the mechanical properties of SHCC made in Polyvinyl alcohol (PVA), Polyethylene (PE) fibers and steel cord (SC), and how this affects the composite property, and ultimately its strain-hardening performance. Also, effect of hybrid type and water-cement ratio on the behavior of SHCC was evaluated in this paper. For these purposes, compressive, four-point bending, and direct tensile tests on SHCC are carried out. As the results of the test, SHCC with water-cement ratio of 0.40 exhibited higher compressive strength, and lower flexural and tensile performance. When water-cement ratio is 0.45, SHCC with only synthetic fibers showed about 2% higher tensile strain. To improve performance of SHCC structural member, however, fiber reinforcing index and fiber strain factor must be improved. Therefore, it is thought that development of hybrid fiber system was needed for workability and economy.
윤현도(Yun Hyun-Do),김선우(Kim Sun-Woo),이민정(Lee Min-Jung) 대한건축학회 2007 대한건축학회 학술발표대회 논문집 - 계획계/구조계 Vol.27 No.1
The cracking behavior and tension stiffening characteristics of normal concrete, strain-hardening cement composites (SHCCs) tension ties under short term imposed load was investigated experimentally. The purpose of this research was to investigate the influence of cement composite damage tolerance on the tension stiffening performance and cracking process of reinforced SHCC tension ties. The effect of loading scheme (monotonic and repeated loading) was also investigated. Testing was carried out on six axially loaded tension tie specimens. Each specimen had a square cross-section dimension of 110 × 110㎜ and length of 500㎜. Improved tension stiffening performance in SHCC contributes to reduced crack widths, i.e., multiple cracking.
CFRP 판으로 전단 보강된 이후 동결융해에 노출된 철근콘크리트 보의 거동 및 음향방출 특성
윤현도(Yun Hyun-Do),김선우(Kim Sun-Woo),이영오(Lee Young-Oh),전수만(Jeon Soo-Man),서수연(Seo Soo-Yeon),최기봉(Choi Ki-Bong) 대한건축학회 2008 大韓建築學會論文集 : 構造系 Vol.24 No.9
External plating of reinforced concrete (RC) structures with carbon fiber-reinforced polymer (CFRP) plate, sheets, or both, is now a widely recognized as repair and retrofit technique. CFRP sheets and plates are being used to strengthen outside concrete structures. The CFRP reinforcements are bonded to beams and slabs using structural adhesives. Adhesive strength can be affected by environmental exposure. During freezing-and-thawing cycling, temperature-induced stresses in the adhesive layer, due to differential thermal expansion between the CFRP and the substrate concrete, may lead to bond damage and contribute to or cause premature CFRP composite separation. This paper presents the results of experimental program undertaken to investigate the effects of freeze-thaw cycling (from -18 to 4℃) on the behavior and failure characteristics of RC beams strengthened in shear with CFRP plate using acoustic emission (AE) technique. The beams were plated with CFRP plate (S system, thickness of 1.2 ㎜, tensile strength of 2,800 MPa) then were subjected to between 0 and 400 freezing-and-thawing cycles. Based on the results presented, freezing-and-thawing cycling between 0 and 120 cycles does not appear to significantly affect the overall load deflection behavior, the crack development, and strain distributions of RC beams strengthened in shear with CFRP plate. But CFRP-strengthened concrete beams exposed to more than 240 freezing-and-thawing cycles exhibited 10% reduction in strength compared to CFRP-strengthened RC beam without being exposed to freezing-and-thawing. The AE-b value derived from the frequency-amplitude distribution of AE signals, was compared with the development of fracture process of CFRP-strengthened RC beams.