EFFECT OF EMBEDMENT LENGTH ON THE PERFORMANCE OF SHEAR-STRENGTHENED RC BEAMS WITH L-SHAPED CFRP PLATES

摘要

This paper presents results of an experimental investigation on reinforced concrete (RC) T-beams retrofitted in shear with prefabricated L-shaped carbon fibre-reinforced polymer (CFRP) plates. Shear-strengthening of RC beams with L-shaped fibre-reinforced polymer (FRP) plates proved to be an effective method. In this method, holes are drilled throughout the beam's flange to fully embed the vertical (perpendicular to the longitudinal axis of the RC beam and in the RC beam's web surface) leg of the L-shaped CFRP plate (Fig. 1). However, in some cases drilling holes in the concrete flange might not be applicable due to presence of obstacles such as longitudinal steel in the flange of the RC beams. Therefore, in this study, the effect of the embedment length of the L-shaped FRP plates in the RC beam's flange to the behaviour of the shear-strengthened RC beams with L-shaped plates is investigated. In total, 6 tests were performed on 2100 mm-long T-beams. Three specimens were strengthened in shear using epoxy bonded L-shaped CFRP plates with different embedment lengths of the plates in the RC beam's flange. One specimen was shearstrengthened with fully-embedded CFRP plates in the concrete beams' flange. One specimen was strengthened with partial embedment of the L-shaped CFRP plate. This specimen is representative of the case that full penetration of the CFRP plate is not feasible due to the presence of an obstacle. In this specimen the embedment length was set equal to 25 mm to simulate the minimum concrete cover thickness in RC beams. One specimen was shear-strengthened with L-shaped plates CFRP with no embedment of the CFRP plate in the concrete beams' flange. For all the specimens strengthened with CFKP L-shaped plates, a set of two L-shaped CFRP plates formed a U-shaped configuration in one cross-section of the strengthened RC beams. One leg of the two L-shaped plates was overlapped and bonded to the soffit of the beams. (Fig. 2). The vertical ending of the L-shaped CFRP plate was epoxy bonded to the hole in the RC beam's flange. In addition, the performance of the strengthened beams with L-shaped CFRP plate was compared with similar specimen strengthened with externally-bonded FRP sheets. Overall, the efficiency of the strengthening method used to retrofit the test specimens was investigated. The experimental shear resistance of each specimen due to FPP divided by the ultimate tensile capacity per unit length of the FRP was calculated to evaluate the efficiency factor of all the strengthened specimens. An analytical model was proposed considering different failure modes of RC beams strengthened with L-shaped CFRP plates such as: FRP pull-out, concrete break-out in the flange, FRP plate debonding and FRP lap-splice failure at the soffit of the beam. The proposed analytical model showed reasonable correlation with the experimental results. The results of this study revealed that RC beams retrofitted with fully-embedded L-shaped FRP plates was the most effective method amongst other strengthening methods in this study. Moreover, partial embedment of the L-shaped CFRP plates was the most effective alternative to the full embedment of the L-shaped CFRP plates when full embedment of L-shaped plates is not feasible. In addition, RC beams strengthened with partially-embedded L-shaped plates showed a superior behaviour compared to those strengthened with externally bonded CFRP plates and sheets.