Experimental Study On The Time-Dependent Effects Of Shrinkage, Creep And Temperature On PC Box Girder Bridge In High-Speed Railway

The shrinkage and creep deformation of PC bridge can affect the smoothness of rail track, and even cause serious damage to fasteners, which may result in serious threat to traffic safety. The temperature effect is the main reason of cracking in the PC beam. The temperature cracks will damage the durability and safety of bridge, especially the concrete box girder. Shrinkage, creep and temperature effects are all time-depended, and also have mutual coupling effect.A series of tests, theoretical study and simulation analysis on the effects of the shrinkage, creep and temperature on32m PC box girder were conducted, on basis of beam production process in Tongxiang Beam Plant of Shanghai Hangzhou passenger dedicated line. The main work of the paper is summarized as follows:(1) Based on the creep and shrinkage prediction model of ACI209(1992), the creep and shrinkage prediction model for high performance concrete in passenger dedicated railway bridges was appropriately proposed by introducing the influence coefficients of reinforced constraint, concrete strength and slump of fresh concrete.(2) An economic curing system for box girder of passenger dedicated line was presented applicably to different environmental conditions, depended on comparative experimental study. Natural curing methods corresponding to three different temperature levels were given out. The distribution of the temperature field and thermal stress in box-girder bridge in early age was studied under different curing methods. (3) Tests on shrinkage and creep deformation of box girders in Shanghai-Hangzhou passenger dedicated line was carried out. The results showed that the loading-age of secondary dead load had a significant influence on creep camber of box girder, and the age of60d-120d seemed to be a reasonable loading time.(4) A coupling model of temperature and creep in the range of0?-90?was established, on the assumption that humidity, temperature and thickness were three independent factors. The model combined with the finite element software, is applied to simulate the internal force and deformation of prestressed concrete box beam under the temperature loads.(5) The creep camber of PC box girder is seriously affected by prestressed tension program:such as tension batch, tension time, quantity of prestressed tendons and the controlled stress, according to a similarity model test carried in this paper. Prestressed tension divided into two batches was more properly than completed in a one-time. It does make sense to delay the final tension time to28d age, in controlling the long-term deformation of PC beam.