Performance evaluation of different anchorage systems for externally bonded FRP sheets for shear strengthening of concrete structures

Externally bonded fiber reinforced polymer (FRP) composites have been used to increase shear strength of concrete structures. To increase the effectiveness of the strengthening with externally bonded FRP, the premature failure due to FRP debonding should be avoided. As a result, efforts to prevent debonding have led to the investigation of many different kinds of anchorage systems. An effective anchorage system allows externally bonded FRP reinforcements to continue carrying a load even after debonding occurs. In the present study, three different anchorage techniques were investigated for their ability to delay or prevent the debonding failure mode through an experimental program on eight full-scale reinforced concrete T-beams. These systems were (1) discontinuous mechanical anchorage (DMA system), sandwich panel mechanical anchorage (SDMA system), and additional horizontal FRP strips (HS system). The DMA system consisted of two hybrid FRP plates bonded together with epoxy then anchored firmly in place with epoxy and concrete wedge anchors. The SDMA system consisted of a modification to the DMA system in which the ends of vertical FRP strips are wrapped around the first FRP plate and overlapped with a second FRP plate. The HS system was the simplest of the three anchorage systems in which additional horizontal FRP sheets were applied continuously along the test region at the critical bond locations (i.e., at the end of vertical FRP strips). Results indicated that the SDMA system performed best followed by the DMA and HS systems. In addition, it was found that interaction between the external FRP strengthening and stirrups exists, and furthermore, the use of a mechanical anchorage system affected the level of shear contribution of stirrups. This must be investigated in more detail and integrated into the design of externally bonded FRP shear strengthening.