Strengthening of Reinforced Concrete Flat Slabs to Resist Punching using Different Techniques
Failure of reinforced concrete flat slabs due to punching is very interested subject. The major purposes of this study are to study experimentally, analytically and numerically the effectiveness of the proposed external strengthening techniques to resist punching shear of reinforced concrete flat slabs. The used external strengthening techniques were: (1) external drop panel confined with GFRP sheets, (2) external steel shear studs (Bolts) at different distances (at half slab effective depth and at the slab effective depth from the column face), (3) external GFRP stirrups, at different distances (at half slab effective depth and at the slab effective depth), and (4) external GFRF sheet in the compression side. The experimental program consisted of seven square specimens (1700 x 1700 x 150 mm) with circular column (stub) had 250 mm diameter at its center. The tested specimens are intended to simulate a half scale interior-slab-column connection. All specimens tested as simply supported slabs under one-point static loading at the center of the column. The numerical program was carried out using ANSYS V.19 as nonlinear finite element software program to study the influence of studied parameters. Calibration and verification of ANSYS V. 19 has been done by comparing the results of the load deflection curves, cracks and ultimate loads with the experimental ones. The results showed that both ECP 203-2017  and ACI 318-19  building codes are conservative compared to the experimental results.
The results show that, using external strengthen by GFRP stirrups and steel shear studs (Bolts) on circles located at distance half the slab effective depth and at the slab effective depth after the column face is an effective method to improve: (1) the ultimate punching shear load, (2) maximum deflection, (3) displacement ductility, (4) toughness, (5) secant stiffness, (6) cracks patterns and (7) failure modes.