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

The present investigation deals with the experimental evaluation of the performance of carbon-fiber-reinforced polymer (CFRP) strips used for flexural strengthening in the negative moment legion of a full-scale reinforced concrete 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 lack of proper shear reinforcement), while Category II beams were designed to fail in flexure. A total of five full-scale concrete beams of each category were constructed, instrumented, and tested The responses of the beams in terms of deflections, strains, and modes of failure were examined. It was observed that Category I beams failed by diagonal cracking with local debonding at the top of the beams, while the Category II beams failed by the onset of delamination at the interface of the CFRP strips and the concrete surface, both with and without concrete-cover failure (shear/tension delamination). It was also noted that the CFRP strips were not stressed to their maximum capacity when the beams failed, which led to ductile failures of all the beams. The maximum stress experienced by the CFRP strips was 28.5% of their 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 Category II beams with respect to corresponding control beams.