Test analysis for FRC beams strengthened with externally bonded FRP sheets

Performances of two different types of fiber reinforced concrete (FRC) beams, which are strengthened with three different types of fiber reinforced plastic (FRP) sheets, respectively, are analyzed in this paper. A series of four-point bending tests for beams are carried out to investigate the effect of fiber reinforcement on FRP sheet strengthening. Three types of concrete beams have been tested, which are plain concrete beams for reference, polypropylene fiber (PF) reinforced concrete beams, and polypropylene fiber (PF) together with steel fiber (SF) hybrid reinforced concrete beams. Three strengthening schemes have been used, which are mono-layered carbon fiber reinforced plastic (CFRP) sheet strengthening, mono-layered glass fiber reinforced plastic (GFRP) sheet strengthening and CFRP mixed GFRP bi-layer sheets strengthening, respectively. Crack developing mechanism and variations of displacements with curvatures for different beams are analyzed. Test and numerical simulation results show that PFs and SFs are able to control the propagation of micro cracks, the development of macro cracks in concrete, and to improve the concrete strength. The ultimate failure modes of test beams also chang from peeling-induced debonding into FRP rupture, which shows that the FRP sheets can exert its strengthening effect sufficiently. Test and numerical results indicate it is an effective method for CFRP mixed GFRP to strengthen FRC beams, which can improve the toughness of concrete, reduce strengthening cost and meanwhile enhance bearing capacity of concrete beams. (C) 2006 Elsevier Ltd. All rights reserved.