Research On The Reinforcement Method With Transverse Prestress For Existing Hollow Slab Bridge

Precast concrete hollow slab bridges play an important role in short and medium span bridges because of its advantages of simple structure, shallow superstructure depth, and convenient construction, while a recurring problem is cracking in the grouted joints between adjacent beams. The detailing of hollow slab bridge has been continuously improved during the last four decades of practice, but the cracking problem is still not completely overcomed. The reason is that the detailing improvement did not improve the stress mode of the joints, thus, which can not overcome the deficiency from the root. And at present, reinforcement measures against joints problem are mostly passive and can not take the initiative to improve the stress mode of the joints, while the transverse prestressed reinforcement as an active strengthening method can effectively reduce the principal tensile stress in accord with the mechanics characteristic of the joints, so that the joints no longer crack with the application of transverse prestressing. However, the application of the transverse prestress method is not ripe enough, and there is no practical design method can be used widely, so this paper makes a detailed study on the reinforcement method with transverse prestress of existing hollow slab bridge.Firstly, the transverse distribution results calculated by finite element method and transversely hinge-connected slab method used by the current design are contrasted, and the stress distribution rule of the joints caused by load is discussed in detail by using finite element method, so that the mechanics reason for joints cracking is founded. Then the shortcomings of current design method is analyzed and the result is verified by cracking calculation.According to the stress analysis results of the joints, the transverse tension stress is one of the main stress components that cause the crack of the joints, which can be effectively reduced by the transverse prestressing. Hollow slab bridge model with damaged joints is established using finite element software ANSYS, and transverse prestressing is applied to the damaged model, which verifies the quite good effectiveness of the transverse prestressing for hollow slab bridges with cracking joints. And various factors are analyzed, including the magnitude of transverse prestressing, load position, the area and spacing of the transverse prestressing tension, bonded or unbonded prestressing, crack sliding surfaces friction, the thickness of the concrete pavement and so on, which qualitative conclusions are drawn from. In addition, the stress distributions with and without transverse prestressing are compared, which indicates the stress of joints without diseases can be effectively reduced by transverse prestressing, thus controling the problem of joints cracking.According to the qualitative effect of transverse prestressed reinforcement and qualitative influence of the various factors, the arrangement of transverse prestressing, the selection of prestress materials and construction process are proposed in accord with the transverse stress distribution rule caused by load and transverse prestressing. A simplified elastic support continuous beam model is proposed according with the transverse mechanical characteristics of hollow slab bridge which can be analysised with grid model, comparing with the results of the more accurate finite element method prove the accuracy and applicability of grid analysis method. Thus, the practical method to calculate the magnitude of transverse prestressing is proposed, and forming a complete design method of transverse prestressing reinforcement. Finally the effectiveness of transverse prestressing reinforcement and the correctness of the design method are proved by accomplishing a real bridge reinforcement design for the general width hollow slab bridge of China’s highway bridge.