Punching shear strengthening of flat slabs with EBROG and EBRIG - FRP strips

The present study investigates the strengthening of flat slabs with Externally Bonded Reinforcement "On Grooves" (EBROG) and "In Grooves" (EBRIG) FRP strips and they are compared with Externally Bonded Reinforcement (EBR) FRP strengthening. 28 slabs consisting of one control and 27 strengthened were defined and analyzed nonlinearly. The EBRIG and EBROG strengthening layout consisted of 1- or 2-layer FRP strips under slabs on 2 grooves of 4- or 8-mm width and 8, 10 or 12 mm depth. First, the results of the finite elements (FE) analysis were verified by experimental results available in the literature and it has confirmed that the FE nonlinear analysis can be used to estimate the strengthened slabs behavior. The analysis results of EBR, EBRIG and EBROG strengthened samples showed that the FRP strengthening of slabs in EBRIG and EBROG format, increased the punching capacity of the slab up to 60%, while EBR strengthening could increase this capacity about 28%. The cracking load was increased about 50% compared to EBR strengthened samples. Also, the EBRIG and EBROG strengthening in some of the samples could change the slab failure from shear to shear flexure and the FRP rupture was resulted in them. The grooves width and depth directly affected the cracking load, punching shear capacity and failure type of slabs.