Suppression Of Plate-end Debonding In FRP-plated RC Beams Using FRP U-jackets:an Experimental Study

In recent years,reinforced concrete(RC)beams strengthened with a fiber-reinforced polymer(FRP)plate(referred to as “FRP-plated RC beams” hereafter)has become a widely-used technique for flexural strengthening of RC beams.Such an FRP plated RC beams commonly failed by debonding failure in the form of intermediate crack debonding or concrete cover separation.Compared to IC debonding,concrete cover separation failed in a more brittle manner,and need to be eliminated in design.When the concrete cover separation occurred,the maximum tensile strain of the FRP tension plate is only 20%-40% of its tensile rupture strain,which therefore leads to a low utilization in the tensile properties of FRP materials.In order to suppress the occurrence of debonding,researchers from various countries have proposed different forms of anchorage devices,such as metal anchors,FRP vertical or incline U-jacket.Among those devices,the FRP incline U-jacket is the most convenient and the most durable,which has the most potential to be applied and promoted.In the present study,two series of tests,which both consisted of fibe specimens,were conducted,while the remaining four beams are anchored with U-jacket at the plate end.The major work of the present study includes:(1)investigation on the failure mechanism of FRP incline U-jacket to limit concrete cover separation.(2)investigation on the effect of different width FRP incline U-jacket on the mechanical properties of beams.(3)study on the effect of different layer incline U-jacket on the mechanical properties of the beam.(4)study on the effect of different bonding methods of FRP incline U-jacket and FRP plate on the mechanical properties of the beam.From the present study,the following conclusions can be drawn.(1)under the circumstance in which the U-jacket layer number and the bonding method are in the same condition,the width of U-jacket is increased,which is able to transform the failure mode of the beam from concrete cover separation to intermediate crack debonding.(2)under the circumstance in which that the U-jacket layer number and the bonding method are in the same condition,increasing the width of U-jacket will improve the ultimate bearing carrying capacity,toughness and material utilization of FRP bottom plate.(3)under the circumstance in which the condition of U-jacket layer and U-jacket width are the same,the staggered pasting of FRP plate and U-jacket can improve the ultimate bearing carrying capacity,toughness and material utilization of FRP bottom plate.(4)under the circumstance in which the U-jacket width and the bonding method are the same,increasing the layer of the U-jacket will improve the ultimate bearing carrying capacity,toughness and the utilization of FRP bottom plate.