Strengthening of one-way spanning RC slabs with cutouts using FRP composites

This paper reports the results of tests on fibre reinforced polymer (FRP) strengthened one-way spanning reinforced concrete (RC) slabs with central cutouts. Four wide slabs with cutouts were tested in addition to two narrow slabs without cutouts. Different positions of applied line loads for the slabs with cutouts resulted in different slab bending action and hence different FRP behaviour for the strengthened slabs. All FRP-strengthened slabs achieved a higher load-carrying capacity than their unstrengthened control counterparts. In addition, all strengthened slabs failed by debonding initiating at intermediate cracks (IC debonding) and in the case of the slabs with cutouts, the critical cracks were diagonal and originated from the corners of the cutout. The ability of the FRP to redistribute stresses around the cutout, the failure mechanisms, as well as pre- and post-debonding behaviour of the strengthened slabs was therefore assessed for different load application positions. Strains on the FRP, concrete and internal steel reinforcement, as well as deflections at different positions on the slab surfaces are also reported. An analytical model, which is based on the ultimate moment of resistance about critical crack lines, is also reported and it its predictions are found to correlate well with the experimental results. The analytical model is able to capture the different slab bending actions in addition to the debonding failure of the strengthened slabs.