Vertical Prestressing Effect Analysis Of Long-span Concrete Box Girder

With the improvement of the science,technology and material technology, prestressedconcrete bridge shows its strong competitiveness. But at the same time, the problem isunavoidable. It is obvious that the cracking phenomenon is quite serious in the completedbridge of prestressed concrete box structure, and the box girder web plate oblique cracksaccounted for a large proportion. To prevent web oblique cracks, vertical prestressedreinforcement is arranged in web. According to the statistics for many years, as a shortage ofactual vertical compressive stress，the cracks are still frequent.This paper introduced the current several kinds of commonly method of the loss ofprestress. Background in engineering as an example, The loss of vertical prestress werecalculated with the method of item loss of prestress. By the analysis shows that for prestressedbeam length is shorter, the friction loss is small. Deformation of anchorage, steel retractionloss in various losses is the largest of all, and it’s more difficult to control in theconstruction.The loss caused by elastic compression of concrete were calculated by usingANSYS. The vertical prestress loss with single row and double row were compared. For theloss caused by creep and shrinkage of concrete, it simplified calculation method combinedwith the stress distribution of the box girder web plate and the shrinkage and creep on thevertical prestress loss,and compared the calculation of midas.Based on the above calculation it put forward several optimization design method whichcan improve the effective vertical prestressed. First of all, compared to the hysteresis tensionand conventional tension,the web vertical stress distribution more uniform. And through thecontrast analysis, stress distribution of hysteresis prestresed one beam section of the web hasbeen more ideal. Second, the vertical prestress can be tilted by the layout. It can effectivelyenhance the efficiency of prestressed and compressive stress web reserves. Finally,throughthe analysis of vertical prestress diffusion rule,It can raised the mothod of determinatingarrangement spacing determination under the spread Angle and the stress level ofcorresponding vertical prestressed. Combined with reference and this article,it had proved therationality of these optimization measures in engineering application.