Shear Strengthening of RC Beams Using Externally Bonded and Anchored FRP U-wraps

Abstract

Externally bonded FRP U-wraps are a common shear strengthening configuration for RC beams, however premature debonding of the wraps is a major problem, which limits the effectiveness and efficiency of the FRP strengthening. In this investigation a new π-shape carbon anchor was used to fasten the FRP U-wraps to the concrete in an attempt to prevent/delay debonding of the wraps and increase their effectiveness. Fourteen large scale rectangular beams with a 1900 mm span, 400 mm height, and 170 mm width were tested in three-point bending with various configurations of FRP shear strengthening. Shear pre-cracks were introduced in the beams at angles of 30 and 45 degrees in an attempt to control the inclination angle of the shear crack and determine its effect on the FRP shear resistance. The FRP shear strengthening configurations included un-anchored U-wraps, U-wraps with anchors, U-wraps with horizontal strips, and full wraps. The results showed that the use of a variable shear crack inclination angle in the CSA S806-12 (2012) standard led to overestimated shear resistance predictions for beams with a single shear crack, therefore a conservative 45 degree shear crack inclination is recommended for design. The use of the proposed carbon anchors resulted in a 74% increase in shear strength over the un-anchored U-wrapped beams, while only using half the amount of FRP. The use of the anchors also resulted in a 286% increase in the ultimate FRP strain over the un-anchored U-wraps, and allowed the FRP wraps to achieve 58% of their rupture strain. The use of horizontal strips provided similar results to the anchors and may be used as a less labour intensive alternative, but this issue needs further investigation.