Strengthening reinforced concrete beams using fiber reinforced polymer (FRP) laminates

The behavior of reinforced concrete beams strengthened with various types o f fiber reinforced polymer (FRP) laminates is presented in this paper. The experimental program included strengthening and testing 14 simply supported rectangular cross section beams. Each beam was initially loaded above its cracking load. The cracked beams were strengthened with FRP laminates and t hen tested until complete failure. Five available strengthening systems of various types of carbon/glass fiber reinforced polymer (CFRP/GFRP) strength ening materials were used. These materials included two types of CFRP sheet s, bi- and unidirectional GFRP sheets, and CFRP plates. The effects of stre ngthening on deflection, failure load and failure mode, strain, and beam du ctility are discussed. In addition, the influence of different numbers of F RP layers, type of epoxy, and strengthening pattern on the behavior of beam s was examined. The ratio of absorbed energy at failure to total energy, or energy ratio, was used as a measure of beam ductility. It is concluded that, in addition to the longitudinal layers, the fibers or iented in the vertical direction forming a U-shape around the beam cross se ction significantly reduce beam deflections and increase beam load carrying capacity. Furthermore, the presence of vertical FRP sheets along the entir e span length eliminates the potential for rupture of the longitudinal shee ts. The combination of vertical and horizontal sheets, together with a prop er epoxy, can lead to a doubling of the ultimate load carrying capacity of the beam. However, all the strengthened beams experienced brittle failure, mandating a higher factor of safety in design.