Carbon Fiber-Reinforced Polymer Punching Reinforcement and Strengthening of Concrete Flat Slabs

Three different carbon fiber-reinforced polymer (CFRP) systems were used to reinforce new or strengthen existing concrete slabs against punching. Untensioned CFRP plates or only very low prestressed CFRP straps could not prevent brittle punching failure. Strap prestressing of at least 15% of the tensile strength led to a ductile two-peak slab response although the CFRP material systems were brittle. The ultimate load of the unreinforced slabs could be increased by 77 to 118% via a redistribution of forces from the concrete to the strap system. An empirical model was established that is able to estimate the first peak load of all the applied CFRP systems. It takes into account the parameters CFRP plate or strap strength, CFRP geometry, CFRP prestressing level, and punching load of the unreinforced slab. A cantilever strut-and-tie model was established to estimate the second peak load. Both models provide acceptable accuracy.