Shear transfer across cracks in FRP strengthened RC members

Abstract

The shear capacity of unplated reinforced concrete (RC) beams depends on the transverse shear to form the critical diagonal crack (CDC) as well as the transverse shear capacity across the CDC. The latter depends on the reinforcing bars crossing the CDC as they provide forces normal to the CDC that allow the shear to be transferred by aggregate interlock. For steel reinforcing bars, these normal forces can be assumed to depend on the ductile yield capacity of the reinforcing bar. However, the problem is more complicated when dealing with fiber reinforced polymer (FRP) plated RC beams, as the normal force now depends on the brittle intermediate crack debonding resistance of the plate as well as the brittle nature of the FRP material. In this paper, eight push tests have been used to directly determine the contribution of externally bonded (EB) and near surface mounted (NSM) FRP plates to the shear capacity, and these are compared with further six EB and NSM steel plated members. It is shown that plate reinforcement can substantially increase the shear capacity and, surprisingly, that the brittle FRP plates can provide a more ductile shear mechanism than the ductile steel plates. © 2008 ASCE.