Punching Shear Strengthening of Two-Way Flat Slabs with CFRP Grids

Abstract

This article presents the results of an experimental program on two-way flat slabs with central loading. The slabs were designed according to the American Concrete Institute code. One slab without any modification was used as the control and four were strengthened with different carbon fiber–reinforced polymer (CFRP) grid configurations including one with preinstalled and three with postinstalled fiber–reinforced polymer (FRP) strengtheners. For strengthening, 8, 16, and 24 strengtheners were used. A method was developed for predicting maximum loading capacity in slabs strengthened with CFRP grids and epoxy resin used in drilled holes. The results of the experiments show that the proposed strengthening method enhances maximum loading and deformation capacities. Furthermore, the proposed strengthening method prevents brittle failures that may occur under vertical concentrated loadings. The dominant failure mode for flat slabs strengthened with FRP grids is found to be deboning of FRP grids due to the small slab depth. In addition to the increased shear capacity of the slab up to a reasonable value, this method of strengthening is capable of changing slab failure from the shear mode to the flexure mode.