Experimental and theoretical study on flexural behavior of hybrid bonded CFRP RC beams

Fiber reinforced polymer (FRP) composites are widely used to strengthen reinforced concrete (RC) structures due to their high mechanical and durability properties compared to traditional materials. However, intermediate crack debonding (ICD) failure limits the effectiveness of strengthening RC beams in flexure with externally bonded (EB)-FRP laminates. Anchorage of the FRP can mitigate this debonding, enhancing the efficiency of FRP strengthening. Hybrid bonding (HB)-FRP emerged as a viable method for delaying/preventing debonding of EB-FRP RC beams. HB combines adhesive bonding from EB with mechanical fastening through metallic plates, increasing resistance to debonding. While previous research explored the bonding capacity of the HB connection using FRP sheets in single-shear tests, few simplified approaches exist for predicting the bending capacity of strengthened beams. In this paper, the feasibility of HB systems to delay ICD of RC flexural elements strengthened with carbon FRP (CFRP) pre-cured laminates is assessed through experimental and theoretical studies. For this purpose, three RC beams strengthened with CFRP are tested, one using EB and two using HB with different anchor spacings. Results include load-deflection response, flexural capacity and failure mode. Experimental results are compared to literature provisions. Results show that the HB technique consistently improves the flexural performance of the beam in all considered cases.