Effect of beam size and FRP thickness on interfacial shear stress concentration and failure mode of FRP-strengthened beams

Abstract

This paper presents the results of an experimental research program designed to study the interfacial shear stress concentration at FRP cut-off points and the failure modes of RC beams strengthened in flexural with externally bonded carbon fibre reinforced polymer (CFRP) sheets. The test variables include the RC beam size and the CFRP thickness. The objectives are to investigate the effects of reduced scaling and the influence of the FRP thickness on the interfacial shear stresses and the failure modes of the FRP-strengthened beams as well as to confirm the validity of proposed analytical models for the prediction of intermediate crack-induced interfacial debonding and interfacial shear stresses at FRP cut-off points. The experimental works involve flexural testing of 17 FRP-strengthened beams under third-point loading. Three different effective beam depths and two CFRP thicknesses are considered. Two main conclusions are drawn from this study. First, the increase in beam size and/or FRP thickness is found to increase the interfacial shear stresses in the FRP curtailment region. In the present study, however, the peak shear stresses are not high enough to cause a change in the failure mode of the beams. Second, the size of the beam does not seem to affect the extent (measured in term of a strengthening ratio, SR) to which a reinforced concrete beam can be strengthened.