Experimental Research On Reinforced Concrete Beams Retrofitted With Near Surface Mounted FRP Reinforcement

The performance of concrete beam with tiny-crack under repeated overload condition was studied in this paper by experimental method. The conclusion can be used to simulate actual status of the existing bridge. Based on the purpose of the subject, orthogonal tests of 27 concrete T-section beams were conducted to study the failure condition, bearing capacity, deformation features of the enforced beam, and the influence on issues discussed above by test parameters. Followings were the final conclusions.The ultimate bearing capacity of the concrete T-section beam with tiny crack can be dramatically improved through reinforcement with Near-Surface Mounted FRP plates or bods. Meanwhile, the rigidity, ductility coefficient and deformation capacity were also improved obviously. With increasing the strength grade of concrete, beam with Near-Surface Mounted FRP reinforcement had higher cohesion strength and ultimate bearing capacity, but the deflection of span center of beams had no significant difference during destruction test. The shear strengthening reinforcement must be guaranteed in order to increase the flexural capacity of the beam and decrease the growth rate of defection.The surface characters of reinforced steel had great affect on the failure condition and ultimate bearing capacity of reinforced beam, while the material category had no discernible effect on bearing capacity. The failure mode of concrete beam reinforced by FRP plate/round FRP fiber was mainly debonding failure of FRP/binder or FRP/concrete. For the beam reinforced with standard deformation fiber (thread FRP fiber,etal), vertical cracks occurred, and thus lead to the split and flaking of the concrete protection layer.For the beam with tiny crack, the cracking level had no obvious effect on the bearing capacity, but it had impact on the deflection quantity. With cracks growing, the beam had greater deflection. The overload extent and repeated times also had no obvious effect on the ultimate bearing capacity. When the overload remained in a certain range, the deflection of beam did not change. While the overload extended beyond the range, the deflection dramatically decreased. However, the accumulated deflection of beam was still higher than contrast test beam. With the increase of the overload repeated times, the deflection of the beam decreased, and the decay rate also decreased.According to the result of the experiment stated above, the theoretical and experiment results on the bearing capacity of no-crack reinforced concrete beam and its related aspects can be applied to analyzing the beam reinforced with FRP. Meanwhile, the theoretical and experimental results of both overloaded and non-overloaded reinforced concrete beams and their related aspects can also be used to study the reinforced beam under overload condition.As the surface character of FRP fiber has a significant influence on bonding strength and bond-slip relation, for the computation work of embed beam with FRP, it is suggested to consider the effect of the surface character of FRP, specially focus on the impact of parameter a. According to experiment data and theory analysis, the paper proposed the statistical formula to calculate the bonding strength and effective length of the beam with Near-Surface Mounted FRP reinforcement, and modified the model for the equivalent tension strain of concrete beam. The paper also verified the formula for bearing capacity (including normal section and of oblique section) of beam with Near-Surface Mounted FRP reinforcement, the computation result fitted well with experiment data, and was more conservative than designed value.The conclusion of this paper laid the foundation for local standard<The handbook of design and construction for concrete beam bridge with NSM FRP reinforcement> in Liaoning Province.