Effectiveness of CFRP strengthening on curved soffit RC beams

The objective of this research program was to study carbon fiber reinforced polymer (CFRP) strengthening of reinforced concrete (RC) members which have concavely-curved soffits. In the presence of such curvature, the FRP laminates attempt to straighten under tension, leading to direct transverse tensile stress at the adhesive-concrete interface, which may cause premature peeling. This tensile stress could also lead to concrete cover delamination. Ten beams, each 6 m in length and having the same soffit curvature (i.e., 4 × 10 -5 mm-1 or in-1), extending over 1, 3 and 5 meters, were tested under three-point static flexure. Two different types of CFRP strengthening techniques, namely wet layup laminates and pultruded precured laminates, were used for external strengthening. One of the beams strengthened with CFRP wet layup laminates (with a curved soffit over an extent of 5 m), used glass FRP spike anchors to prevent peeling. Beams with soffit curvature limited to an extent of 1 m, failed at similar loads when compared with control specimens containing flat soffits. For beams having a soffit curvature extending over 3 and 5 m, reduction in strength was observed because of premature peeling. Inclusion of the GFRP spike anchors with the wet layup system led to a performance superior to the control specimen (flat soffit) confirming that application of GFRP spike anchors delays premature peeling