Experimental and numerical study of two-way flat slab strengthened with the FRP strengtheners is presented in this thesis.   Twenty two slabs with 85 and 105 mm thickness, 1200 mm width and length, with different reinforcement ratio and compressive strength was made; in which three of the slabs served as a control ones and the other with a screw and nuts, as well as innovative techniques, including the use FRP rod, FRP grid and FRP fan using two component epoxy glue were strengthened. For strengthening 8, 16 and 24 arrangements of strengtheners around the 150 square millimeters loaded plate was used. Samples were loaded smoothly through a steel plate in the center of the slab through a hydraulic jack until failure of slabs.

   The various modes of failure were observed in these sla   for the control slab, the failure mode was a punching shear failure while for the strengthened slabs, various modes of shear - bending and bending was observed in different cases. In slab with 8 strengtheners, shear failure mode, and in slabs with 16 and 24 strengtheners, shear - flexural and flexural modes were observed. With changing in failure mode, deformation increasing from 200% to 400% and the ductility increased from 100% to 300% in the strengthened slab. In the strengthened slab shear capacity increasing from 15% to 120% was observed compared to the control slab. Finally, the results of strengthened slabs were compared with the proposed equations by the ACI and JSCE.Two cases were studied; around the loading plate and extended area of punching shear. In the first case, increasing the capacity up to 170% of the code results and in the second case increasing the capacity up to 60% was observed. Dispute over the results of the test results with the code results, show the effectiveness of the method has been used for strengthening. The study has shown that the ACI Code equations in punching shear respect to the JSCE ones are conservative; and on the other hand the JSCE equations in this case are more realistic.