Shear strengthening of T cross section reinforced concrete beams by near-surface mounted technique

With the purpose of evaluating the influence of both the percentage and inclination of the carbon fiber-reinforced polymer (CFRP) laminates on the effectiveness of the near-surface mounted technique for the shear strengthening of reinforced concrete T beams, an experimental program was carried out, using three percentages of laminates and, for each one, three inclinations: 90, 60, and 45 degrees. The CFRP-strengthened beams had a steel stirrup reinforcement ratio (rho(sw)) of 0.1%. The highest CFRP percentage was designed to provide a maximum load similar to the one of a reference beam reinforced with rho(sw) equal to 0.24%. Although these beams have had a similar maximum load, the beams with CFRP presented higher stiffness. Laminates at 60 degrees was the most effective shear strengthening configuration, having provided a maximum increase in the load capacity of 33%. The contribution of the CFRP strengthening systems was limited by the concrete tensile strength. Below certain spacing between laminates, a group effect occurs due to the interference between consecutive concrete failure surfaces, leading to the detachment of "two lateral walls" from the underlying beam core.