Shear Behaviour of Concrete Beams Retrofitted with Anchored CFRP Wraps at Elevated Temperatures

Different anchoring techniques such as metal plates and bolts, U-shaped FRP jackets, FRP anchors have been used to delay the premature debonding of the FRP sheets in strengthened concrete structures. Among these, FRP anchors are more suitable since they can be applied simultaneously with the FRP sheets and are corrosion resistant. Anchored FRP sheets have shown promising results for both shear and flexure strengthened RC structures under room conditions. Due to the changing climate, structures are now exposed to higher than usual temperatures, so it is important to understand the behaviour of these anchored FRP sheets under elevated temperatures. The current study examined the thermal behaviour of four large-scale shear-critical steel-reinforced concrete beams, one unwrapped and three strengthened with a single layer of CFRP sheet and CFRP anchors. The beams tested at room conditions were monotonically loaded to failure, while beams tested at elevated temperatures (40 and 60 °C) were first subjected to a combined sustained load and elevated temperature during the 24 h conditioning period and then monotonically loaded to failure at that temperature. The tests showed the failure of the unwrapped beam by the rupture of a steel stirrup leg and that of the strengthened beams by pull-out of anchors accompanied by debonding of FRP sheet. A single layer of anchored CFRP wrap improved the beam strength by about 96% at room conditions, 101% at a temperature of 40 °C, and 88% at 60 °C. The midspan displacement also increased by 133% as a result of FRP wrapping at room conditions while exposure to 60 °C reduced this improvement to only 68%. A comparative study was also carried out to evaluate equations available in different FRP standards for shear strength predictions.