Destructive Test And Strengthening Technology Of In-Service PC Plate Beams In Seasonal Frozen Zone

Because of the advantages of low building height,simple structure,convenient construction and good economy,the prestressed concrete slab beam(PC slab beam)is widely used in medium and small span bridge construction in China.With the increase of service time,the frequent action of heavy vehicles and the environment effect,the medium and small span bridge diseases and damages frequently occur,bearing capacity decreases and service performance decreases.The proportion of dangerous bridges in seasonal frozen area is obviously higher than that in other areas because of the adverse environment such as freeze-thaw and salt-freeze.The destructive tests and reinforcement technologies of bridges which have been in service for 20 years in seasonal frozen areas were carried out.The main contents are as follows:(1)Three four-point bending loading test conditions of 2.0m,3.9m and 5.2m bending length were designed.Destructive tests and non-linear finite element simulation of five in-service beams were carried out.The failure process,failure models,bearing capacity and stiffness degradation of old bridges beams under four-point bending loads were studied.The results show that the service performance of the test beam is degraded,but the ultimate bearing capacity still meets the requirements.Prestressing steel strand at beam end has slipped during structural failure.The failure modes of structures gradually change from bending failure to shear failure.(2)Three single-point loading test conditions of 1.8m,2.7m and 3.9m length of shear-bending section were designed.The destructive tests and nonlinear finite element simulation of three PC slab beams under single point concentrated load were conducted.The failure process,failure mode and bearing capacity of old bridge beams under single point load at the end of slab were studied.The results show that the service performance and ultimate bearing capacity of test beams are obviously degraded.Prestressing steel strand at beam end has slipped during structural failure.The failure modes of structures ware shear failure.A method for calculating the shear capacity of prestressed reinforced concrete beams based on truss-arch model was proposed.The accuracy of the model is verified by the results of this paper and other relevant shear tests collected.(3)The destructive tests of 16m span PC slab beams reinforced with ordinary carbon fiber-reinforced plastics(CFRP)sheet and prestressed CFRP sheet under four-point bending loads were taken out The effects of different bending reinforcement technologies on the mechanical behavior and bearing capacity of PC slab beams in service during the process of loading were obtained compared with the unreinforced beams.The results show that the three reinforcement methods can effectively improve the service performance and ultimate bearing capacity of the structure.Based on the failure test results of old bridge beams reinforcement with CFRP sheets,the calculation model of crack spacing and crack width of concrete beams strengthened with CFRP sheets under secondary loading was revised.The calculated value of the model is in good agreement with the experimental results and the relevant collected experimental results drawn by other scholars.(4)The destructive tests of PC slab beams under single point load at the end of slab were conducted which reinforced by two shear reinforcement technologies,such as increasing section height and sticking steel plate at the end of slab.The destructive tests of 16m span PC slab beams under four-point bending loads were carried out which reinforced by three shear reinforcement technologies,such as three-side enclosed concrete,four-side enclosed concrete and plate end filled concrete.The effects of different shear reinforcement technologies on the mechanical behavior and bearing capacity of PC slab beams in service during the process of loading were analyzed comparing with the unreinforced beams.The results show that the five reinforcement methods can effectively improve the service performance and ultimate bearing capacity of the structure.The method of enlarging the section of three-sided concrete and four-sided concrete make the failure mode of structure change from shear failure to bending failure.(5)A new shear reinforcement technologies of PC slab beams hinged joints with reinforcement was proposed.The destructive test analysis of PC slab beams reinforced under single point load and four point bending load was conducted,and the reinforcement effect was compared with that of unreinforced beam,which verifies the effectiveness of the new technology of shear reinforcement with hinged joints.The results show that the two reinforcement methods can effectively improve the service performance and ultimate bearing capacity of the structure and make failure mode of the structure gradually changes from shear failure to bending failure.