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강섬유 혼입량 증가에 따른 고강도 콘크리트 재료특성의 변화
김윤일,박동순,서치호 대한건축학회 2005 大韓建築學會論文集 : 構造系 Vol.21 No.2
In this paper, concrete material tests were carried out to investigate variations of workability, compressive and splitting tensile strength, and flexural strength and toughness characteristics of steel-fiber reinforced high-strength concrete according to increase of fiber volume. Test specimens were arranged with six levels of concrete compressive strength, 30㎫, 50㎫, 60㎫, 70㎫, 8㎫, 90㎫ and fiber volume ratios, 0.0%, 0.5%, 1.0%, 1.5%, 2.0%. The test results showed that effects of steel fibers in improvement of concrete splitting tensile and flexural strength were more distinguished in high-strength concrete than general strength concrete.
地震荷重을 받는 鐵筋콘크리트 骨造의 塑性힌지部移動 및 擴張에 관한 實驗的 硏究
金潤一 관동대학교 1991 關大論文集 Vol.19 No.2
Recent several investigations have suggested relocating beam plastic hinging zone to prevent the damage in the beam-column joint caused by the penetration of beam reinforcement yielding. But this design concept has some problems: 1) The use of the relocated plastic hinge design imposes a higher rotational ductility demand on moving plastic hinge section to achieve the required displacement ductility factor, especially in a beam with relatively small span-to-depth ratio. Moreover, there is a significant increase in the number of inelastic deformation reversals combined with a high rotational ductility demand. 2) When beam plastic hinge is relocated by the intermediate longitudinal reinforcements and supplemental top and bottom flexural reinforcements properly cut off or anchored into the beam, the energy dissipation capacity of a beam-column subassemblage is little enhanced even though these supplemental reinforcements are used. Therefore, it is considered that the relocated plastic hinge design concept should be modified in a beam subjected to high ultimate shear stress, as priority being given to enhancing enegry dissipation capacity of the beam and reducing curvature ductility demand increased by relocating beam plastic hinging zone, rather than ensuring elastic beam-column joint response even at a high displacement ductility factor. The primary objective of this investigation was to develop a modified design concept which could enhance the hysteretic behavior of a frame and simultaneously reduce the damage of the beam-column joint, particularly in the reinforced concrete frame that has beams subjected to high ultimate shear stresses or with small span-tn-depth ratios. In this study, 9 full-size exterior beam-column subassemblages were tested under cyclic loads. Based on the test results, the following conclusions were drawn: 1) Intermediate layers of longitudinal reinforcement over a specific length in a beam can be used to relocate the beam plastic hinging zone some distance away from the column face for avoiding the damage in the beam-column joint resulted from the penetration of beam reinforcement yielding, but it is considered that in a beam subjected to high ultimate shear stress, more supplemental shear reinforcements are required at the relocated plastic hinging zone to enhance the energy dissipation capacity of the beam. 2) In a beam subjected to high ultimate shear stress(about more than 3.5 f'c psi, 0.93 f'c kg/㎠), or with small span-to-depth ratio relatively(about less than 7), modified design concept, using some flexural bent reinforcement crossed diagonally at one beam depth away from the column face, can be used to enlarge the relocated plastic hinging zone for improving hysteretic behavior of the beam and reducing rotional demand increased due to relocating plastic hinging zone. 3) When plastic hinging zone is intended to be relocated away from the column face by using some flexural bent bars(X shape), it is considered that nominal moment capacity of a beam should be above 1.2 times anticipated acting moment at the column rice, and the angle of bent bars would be suitable for the range of 45°-60°.