단면증대 무근 콘크리트 기둥의 성능평가

Abstract

Recently, the needs for structural remodeling, which include the change and move of structural elements, have increased in Korea. This induce the increasing axial capacities of vertical elements like column and wall. A method for increasing axial capacity is very limited, and RC jacketing method is used widely in Korea. One of the biggest problems of this kind of elements are cracking of repair material, and repair material debonding from the concrete substrate. There are few researches about mechanisms and characteristics bond between existing concrete and repair materials. This mainly due to the lack of understanding and guide lines of the surface roughness of substrate. This study quantified the surface roughness of the chipped specimen by using self-made measurement jig for measuring surface profile, and compression test for non-reinforced concrete columns. Experimental values are the ratio of the area between retrofitted column and existing column, and the preparation of surface roughness. The ratios (area of retrofitted column / area of existing column) are 2.25 and 4, and the surfaces are chipped (hand-chipped and electric – hammer - chipped) and non-chipped. The conclusion is as follows. (1) The analysis of the surface roughness profile through the instrument shows that the Arithmetic mean deviation, maximum height and relative height are almost similar but there exists poor correlation between the profile length and the average mean period of profile roughness. (2) The comparison of the maximum load shows that the axial performance decreased by 15% maximum compared to the expected maximum load under the RC jacketing method and the maximum strength of chipped specimens increased by about 4% compared to the case non-chipped specimens. (3) The comparison of the correlation between 5 surface roughness indexes (Arithmetic mean deviation, maximum height, relative height of profile length and mean period of profile roughness) and the maximum strength through the linear trend analysis shows that the profile length and the maximum strength is 0.26, much larger than the other surface roughness index (0.057 - 0.138), meaning that the profile length holds the largest correlation with the roughness ability of the member under the axial load. (4) The horizontal expansion appeared based on the Poisson ratio by the elastic movement up to 40% of the maximum load. Then, it depended on the internal damage and cracks of the specimen and the distortion rate by the vertical expansion dramatically increased around 80% of the maximum load.