Behaviour And Strength Of Rc Beams Flexurally-Strengthened With NSM FRP And Anchorages

Flexural strengthening of RC beams through the Near-surface mounted(NSM)fiberreinforced polymer(FRP)method has attracted an increasing worldwide attention in the last two decades.It has been found by a large number of experimental studies that although the bond efficiency between NSM FRP and concrete is high,premature debonding failures were still frequently observed.Such debonding failures limited the strengthening efficiency of NSM FRP as well as the performance of RC beams strengthened in flexure with NSM FRP(referred to as NSM-strengthened beams hereafter for simplicity).To mitigate/prevent the debonding failures of NSM-strengthened beams,proper anchoring measures can be used.However,the relevant studies are very limited,with accurate numerical models and design methods still lacking.The application of NSM FRP strengthening method in practice is therefore limited.Against the above background,this paper presents a combined experimental,numerical and theoretical study on the debonding and anchoring of NSMstrengthened beams.In terms of experimental study,an experimental program consisting of 16 full-scale reinforced-concrete(RC)beams was carried out.The effect of load distribution on the mechanical behavior of NSM-strengthened beams was first investigated.Then,the anchoring effects of FRP U-jackets with different parameters on the behavior of NSMstrengthened beams were investigated,and the failure mechanism of such strengthened beams was clarified.Finally,a novel embedded FRP anchor was proposed for conditions in which the use of FRP U-jackets was not suitable.In terms of numerical study,the nonlinear finite element(FE)model of NSMstrengthened beam was first developed.Using the proposed FE model,the failure processes of NSM-strengthened beams under different load distributions were accurately simulated,and a parametric study was conducted to investigate the effect of load uniformity on the behavior of NSM-strengthened beams with different embedded length of NSM FRP.The proposed FE model for NSM-strengthened beams was then further developed to incorporate FRP U-jackets,and was used to expose the failure processes of NSM-strengthened beams anchored with FRP U-jackets.In terms of theoretical study,the FE model of NSM-strengthened beam anchored with FRP U-jackets was properly simplified,and the simplified FE model was used in a parametric study to generate numerical results,based on which a strength model for debonding failure of such beams was proposed.Based on the above studies,following conclusions can be drawn:(1)the ultimate load at debonding of NSM-strengthened beam increases with the load uniformity;(2)FRP Ujackets can effectively restrain the debonding failure and thus improve the performance of NSM-strengthened beams,and U-jacket parameters have significant effects on the beam behavior;(3)the proposed embedded FRP anchor is also capable of mitigating debonding failures of NSM-strengthened beams;(4)the FE models developed in this thesis are able to accurately simulate the behavior of NSM-strengthened beams without/with FRP U-jackets;and(5)the proposed strength model for debonding failure of NSM-strengthened beams with FRP U-jackets can give close predictions to the test results.