Innovative Repair Technique for RC Beams Predamaged in Shear

Abstract

The one major practical difficulty associated with reinforced concrete (RC) structures strengthened with externally bonded (EB) carbon-fiber-reinforced polymer (CFRP) sheets is that they must be bonded to a hard uncracked concrete surface, which need may not be met in many cases. This paper assesses the usage of a temporary compressive force that was applied parallel to the beam depth in the cracking-shear zone in order to close all the existing shear cracks prior to the application of the CFRP-strengthening sheets. This force was kept constant till full curing of the CFRP epoxy adhesive, and after the epoxy had cured, it was completely removed. The advantages that result from the shear strengthening of RC beams using the new proposed technique are that closing of all existing cracks and removing the temporary compressive force generates tension force in the CFRP-strengthening strips, which in turn delays the formation and propagation of the shear cracks and develops a compressive force in the internal stirrups, which in turn increases their efficiency. These advantages were verified by testing of seven RC beams designed to fail in shear. Two beams were strengthened using the proposed technique, two beams were repaired by epoxy injection before being strengthened using CFRP, one beam was strengthened using CFRP applied directly over the cracked concrete surface, one beam was strengthened without preloading, and one beam was tested without strengthening and served as a control. Finally, the authors present and comment upon a comparison between the present experimental results and the predictions using the available formulations recommended by some international guidelines.