Behavior of precracked RC beams strengthened with carbon FRP sheets

Experimental data obtained from strengthened, precracked, reinforced concrete (RC) specimens are presented together with the results of material characterization. Strengthening was attained with the adhesion of carbon fiber-reinforced plastic (CFRP) sheets to the concrete surface. The CFRP was applied as in situ (i.e., working under the beam). Several variables were investigated, including: two CFRP material systems, two concrete surface preparations, two RC cross sections, and the number and location of CFRP plies. For two specimens, the presence of applied load (simulating the total service load) as well as external prestressing during the adhesion of the CFRP reinforcement, were investigated. It is shown that the effect of CFRP strengthening was considerable, but the effect of some of the tested variables was modest. An existing analytical model has been extended to simulate the load-deflection behavior as well as the failure mode of the precncked RC specimens. Different failure mechanisms from ductile to brittle were simulated and verified, adopting the mechanical properties of the constituent materials obtained via standard tests or using a simple test for the concrete-adhesive interface.