Experimental and numerical studies for EFECT of taper layered CFRPs on strenthening RC beams

This paper focuses on evaluation of strengthening effect of taper layered CFRPs (Carbon Fiber Reinforced Polymers) used to strengthen RC (Reinforced Concrete) beams. Toward this goal, experimental studies are performed on RC beams strengthened with various layers and types of CFRP sheets. Also, moment capacities are investigated using equations suggested from existing design manuals such as ACI and ISIS, and the numerical results are compared with the experimental results. For the experiments, CFRPs are externally attached to the bottom surface of RC beams which sizes are 200mm×250mm×3200mm (width×height×length). Variables of this study are the number of CFRP layers and length of each layer, so two, three, or four layers of CFRPs are used for strengthening and different lengths of CFRP layers are prepared. As A type, RC beams are strengthened with same length of CFRPs, while RC beams for B type are strengthened with CFRPs which length of each layer becomes shorter as attached later. From four point loading tests, load-deflection relations of the beams and strain distributions of CFRPs are obtained. Experimental results shows that the RC beams with taper layered CFRPs show the better strengthening effect than the uniformly ended CFRPs, especially when the beams are strengthened with three or more layers of CFRPs. The reason is because taper layered CFRPs reduce stress concentration at the end of CFRPs layers and delay failure due to dobending of CFRPs. From numerical studies, it is found that the existing numerical models do not consider the strengthening effect due to taper layered CFRPs, and are not able to distinguish moment capacity of RC beams with taper layered CFRPs from RC beams with uniformly ended CFRPs.