Nowadays, flat slabs has been frequently used in the construction, parking and bridges beacuse simple implementation and the architectural beauty of this system. However, there are some particular problems with this system, one of the most important problems is creating the punching shear. Punching shear is the sudden brittle failure, for this reason many studies is done to retrofit flat slabs against of punching shear. In this paper will be tried to offer a new technique for retrofitting in flat slabs against punching shear. In this study will be used of strew, CFRP, GFRP rods also CFRP, GFRP grids to retrofitted flat slabs. Therefore, spans of the structure analyzed were 3.6 m by 3.6 m bays in two directions with 4 kN/m2 dead and 5 kN/m2 live loads in addition to the slab self weight due to a depth of 125 mm. Computational percentage of the bending rods in this slab is equal to 1 percent, but in order to punching shear failure occur in all simulated samples, maximum bending rods that is equal to 2.7 percent is used. To achieve the purposes of current study, 31 flat slabs with dimensions of 1800 × 1800 × 125 mm were simulated with a finite element software called ABAQUS, including a sample without strengthening as the control sample and 30 samples are strengthened with 5 methods. Load was applied on rigid 150 × 150 × 10 mm steel plate to center of these slabs. In each of five methods, in order to properly install screw bolts and FRP rods in the slabs around the 150 × 150 mm loading plate in the center of the slabs, two arrangement of radial and orthogonal were used. The results of current study showed that the use of bolts and grids increasing the capacity of the punching shear in flat slabs.Also, despite using approximately 2.5 times composites in the bolts against of the grids, but they have almost equal punching shear capacity. among slabs strengthened with bolts, slabs strengthened with bolts and orthogonal arrangement that distance of them is 50 mm showed perform better than the rest of the arrangements. In addition, in this study, CFRP bolts showed the best performance of strengthening slabs. Key Words: Strengthening flat slabs, Punching shear, Two-Way slabs, Slab-Column connection, FRP bolts, FRP grids.
