炭素 FRP로 補强된 R.C 보의 휨 擧動

Abstract

Carbon FRP sheets or plates as advanced composites seem to gradually play a significant role in future construction applications, especially in the strengthening and rehabilitation of existing bridges. Such techniques as external prestressing and epoxy-bonded steel plate have been used successfully to increase the strength of girders in existing bridges and buildings. Because of the advantages of composite materials such as immunity to corrosion, a low volume to weight ratio, and unlimited delivery length thus eliminating the need for joints, Carbon FRP sheets and plates as high strength composites are an efficient substitute for the steel plating method. This paper presents the flexural behavior and strengthening effect of reinforced concrete beams strengthened using glued-on carbon fiber reinforced plastic(CFRP) sheet or plate. Parameters involved in this experimental study are the number of CFRP sheet or the bond length of plate and whether there is web anchorage or not. In general, normally sheet-strengthened beams with no web anchorage were failed by delamination shear failure within concrete. The delamination occurred suddenly and the concrete cover cracked vertically and diagonally by flexure and shear was spalled off due to the released energy. The sheet-strengthened beams were stiffer than the reference beam before and after steel yielding. On the other hand, sheet-strengthened beams with web anchorage were finally failed by CFRP sheet rupture after reaching their maximum ultimate loads. The ultimate load considerably increased with an increase of strengthening level. However, the ultimate deflection curvilinearly decreased. The sheet-strengthened beams with web anchorage had slightly increased ultimate loads and high ductility in their ultimate deflection. Therefore, the increment of the load obtained by strengthening was curvilinearly proportional to the strengthening level. The shape of strain distribution of CFRP sheet was very similar to that of bending moment diagram. Based on the assumption of constant shear stress in the analysis of delamination shear stress of concrete, the average shear stress of concrete at interface ranges between and (in ) depending on strengthening level. The plate-strengthened beams with no web anchorage were generally failed by concrete cover failure along the longitudinal reinforcement. On the other hand, plate-strengthened beams with web anchorage were finally failed by delamination shear failure within concrete after breaking of CFRP sheet wrapping around web. The ultimate load and deflection of plate-strengthened beams increased with an increased bond length of CFRP plate. Also, the ultimate load and deflection increased with an increased anchorage length of CFRP sheet. Particularly, the plate-strengthened beams with web anchorage maintained high ultimate load resisting capacity until very large deflection. The shape of strain distribution of CFRP plate along beam was very similar to that of bending moment diagram. Therefore, an assumption of constant shear stress in shear span could be possible in the analysis of delamination shear stress of concrete. In the case of full bond length, the ultimate resisting shear stress provided by concrete and CFRP sheet increased with an increase of web anchorage length from to (in ). In the resisting shear force, about shear force was provided by FRP anchorage sheet.