Investigation of the Force Transfer Mechanisms for Open Hoop FRP Strips Bonded on R/C Beams with or without Anchoring Devices

The present study investigates the force transfer mechanisms for open hoop fiber reinforced plastic (FRP) strips attached at reinforced concrete (R/C) beams with or without anchorage. These open hoop FRP strips are utilized in R/C beams that are in need of shear capacity upgrade. This type of retrofitting is necessary for R/C structures designed with less stringent seismic loading conditions than those currently required. For this purpose special unit beam concrete specimens were fabricated and were used to attach open hoop carbon (CFRP) or steel (SFRP) FRP strips with or without anchoring. A novel loading arrangement was utilized to apply the necessary forces to these unit beam specimens together with instrumentation capable of capturing the behaviour of these specimens up to failure. Studying in this way the transfer of forces from the open hoop FRP strips, it could be demonstrated that when this type of retrofitting was accompanied with a properly designed anchoring device, a significant increase in the bearing capacity of the tested specimens was observed. Moreover, the observed failure was that of the fracture of the FRP strips for all such specimens. The highest degree of FRP material exploitation was achieved in the specimen that utilizes a patented anchoring device together with two layers of SFRP strips. Debonding of the FRP strips or failure of the anchoring device results, as was to be expected, in relatively unsatisfactory FRP material exploitation.