Experiment Study And Theoretical Analysis Of Reinforced Concrete Torsion Member Strengthened By FRP

With the increase of structural strengthening and retrofit projects, strengthening capability and design method of structures and members subjected to various load types are becoming one of the most attractive research topics in recent years, among which study of strengthening torsion members lacks of thorough research because of the complicated mechanism. Strengthening reinforced concrete member with FRP (fiber reinforced polymer) is a kind of new strengthening technology. The experiment study on reinforced concrete members strengthened by Carbon FRP and Aramid FRP is performed, on the basis of which the torsion behavior, failure mechanism and calculation method of loading capacity are investigated. The reinforced concrete torsion members with rectangular section and T-shape section are tested in the experiment with the strengthening of CFRP or AFRP strips. The torsion behavior and failure mechanism of torsion members are studied with respect to cracking torque, ultimate torque, torsional deformation and failure type, and furthermore the influences of FRP wrapping style and FRP usage to strengthening effect are analyzed. The experiment results show that the ultimate tension strain of FRP is much less than that of FRP material when the strengthened torsion member fails. The reason is that the tension failure of FRP is due to the torsional deformation and interaction of two-side concrete among inclined cracks, which is a process from local failure to integration failure.On the basis of experiment study, the mechanical model of reinforced concrete torsion members strengthened by FRP is presented with respect to spatial truss model theory of inclined compression field considering concrete softening, on the basis of which the calculation formulae of effective stress of FRP and ultimate loading capacity of strengthened torsion members are derived. The analysis program of FRP strengthened torsion members is developed considering nonlinear stress and strain relationships of reinforcement, concrete and FRP. On the basis of calculation formula of torsion members described in code for design of concrete structures, the modified formulae of strengthened torsion members with rectangular section or T-shape section are put forward together with the design and construction suggestions of strengthened torsion members.In order to guarantee the ductility of reinforced concrete torsion members strengthened by FRP, the FRP usage should be controlled so that the reinforcement in the member will yield and the ductile characteristics of failure is assured. On the basis of reinforcement settings described in the code, the appropriate FRP usage is presented so as to avoid brittle failure because of FRP overabundance.