Experimental and numerical evaluation of punching strength of RC flat slabs strengthened using FRP fabrics

Punching failure is the critical phenomenon in isolated footing as well as in flat slabs, because of high shear concentration near the column vicinity. Numerous existing flat slab structures have inadequate performance, which may be resulted on by changes in accommodations, poor design and construction methods, noncompliance with new codal guidelines, etc. One possible way of enhancing structural performance of existing flat slab structures through strengthening against punching shear. Fibre-reinforced polymers (FRP) are composite materials gained acceptance in strengthening structural elements by wrapping them on to face of the structures along with epoxy adhesive. Design approaches to predict the punching shear strength of flat slabs are empirical and their prediction is irrational. In this paper, experimental behavior of a slab-column specimens strengthened using carbon FRP (CFRP) fabrics in orthogonal and skew pattern are presented and a mechanical model based on the critical shear crack theory (CSCT) is modified to predict the punching strength of fibre-reinforced polymers strengthened slabs.. Additionally, finite element model (FEM) of strengthened slabs are proposed and validated the non-linear finite element analysis (NLFEA) results with experimental results. The ultimate punching failure load will be significantly increased by the addition of CFRP to the tension face, which was about 37 and 51%, respectively, in orthogonal skew wrapping arrangements. The proposed model is based on the force carried by a critical shear crack and the load rotation relationship of an isolated slab-column model. The CSCT takes into consideration the pattern of wrapping, quantity of reinforcement, and FRP properties to predict punching strength. The results from CSCT and NLFEA demonstrates a very good agreement with experimental punching failure loads with very low Variance of 3.07 and 1.5%, respectively. The CSCT model is versatile and amply FRP strengthening in the prediction.