The Application Of The Externally Prestressed Technique In Continuous Rigid Frame Bridge

Chinese bridge construction climax makes a good chance for technology of concrete members prestressing with external tendons to be applied and developed. In engineering reinforcement,because of the advantages of simple construction,struceural safety,easy maintenance and economy,the external prestressing technique has been widely used in the new construction of large civil engineering structures.Also,many engineering structures at service,such as large span beam and bridges,are suffering from fatigue or structural harm due to structure aging,corrosion of reinfor-cement bar and overweight. It is very effective to strengthen these harmed or fatigue structures using the externally prestressing technique.This article introduces the basic principles of bridge reinforcement. It should be used different methods of prestressed reinforcement to reinforce different bridges. Through the analysis of simple-span bridges and continuous beam bridges,to make curve reinforced is more effective than to make line reinforced to resist load. According to the present formula,this article mainly analysis the different simplified formula to the ultimate stress of external prestressing tendon on the base of theoretical analysis. Influence of various parameters including ratio of unprestressed reinforcement, ratio of external prestressing tendon, span-depth ratio, compressive strength of concrete, and loading pattern on the ultimate stress in tendon, fps, are investigated in detail. Then it can find almost suitable calculated formula of the ultimate stress. In this foundation, then reconsiders the safety coefficient to the bridge design. So it can be used to instruct the design of externally prestressed beam.Through analyse the pressed characters of reforced system within external prestressing, It evaluated the calculational method of normal cross section flexural bearing capacity and normal cross section flexural bearing capacity within reinforced system.Also,it evaluated the calculational method of stress increment of external prestressing tendons and stress deformation are used.Moreover,It put up computations by reinforced examples of PC beams. According to the result of checked calculation, reinforce computational method of vitro pre-stressed is recommended by this article. It's more ideal reflect that the beam's stress situation after has used in vitro pre-stressed reinforcement. The paper researches factors which influence endurance of external prestressing concrete bridges, and then presentsmeasures and suggestions for enhancing it.