Strengthening of negative moment region of reinforced concrete beams usingcarbon fiber-reinforced polymer strips

The present investigation deals with the experimental evaluation of the per formance of carbon-fiber-reinforced polymer (CFRP) strips used for flexural strengthening in the negative moment legion of a full-scale reinforced con crete beam. The flexural strengthening of two categories of beams (I and II ) was considered Category I beams,were designed to fail in shear (due to la ck of proper shear reinforcement), while Category II beams were designed to fail in flexure. A total of five full-scale concrete beams of each categor y were constructed, instrumented, and tested The responses of the beams in terms of deflections, strains, and modes of failure were examined. It was o bserved that Category I beams failed by diagonal cracking with local debond ing at the top of the beams, while the Category II beams failed by the onse t of delamination at the interface of the CFRP strips and the concrete surf ace, both with and without concrete-cover failure (shear/tension delaminati on). It was also noted that the CFRP strips were not stressed to their maxi mum capacity when the beams failed, which led to ductile failures of all th e beams. The maximum stress experienced by the CFRP strips was 28.5% of the ir ultimate strength in the case of Category I beams, and 52% for Category II beams. The maximum increase in load-carrying capacity of the beam due to strengthening was observed to be 29% for Category I beams, and 40% for Cat egory II beams with respect to corresponding control beams.