Study On Longitudinal Shortening Of Prestressed Continuous Girder

The paper is based on the background of the ShiLong Bridge on GuangShen line,by the Finite Element Analysis Model, analyze the shortened statistics of the beam end caused in construction,the cross section stress distribution of the three Architecture (plain concrete, ferroconcrete, Pre-stressed Concrete Structure),and the shortened statistics of the beam end caused by the prestressing degree. Also, cite rebar ratio influence function in order to consider the effects of reinforcement bar on concrete creep. Based on the above theory, here derive some concludes:1. The cause result in the bridge beam end shortened:(1) shrinkage and creep of concrete;(2) prestressed reinforcement;(3) downwarping caused by every load.2. Prestressing Force is the internal cause, system transition is the direct reason.3. In under each kind of factors, the Maximum shortened statistics of the ShiLongBridge Guangzhou side beam end is 82.41mm, and DongGuan side is 118.12mm. All of the factors, creep is the main reason, in the ratio of more than 43%; prestressed reinforcement and Decreases temperature by 15 degree are 20%; shrinkage cracks of concrete is 15%; the influence of the permanent load and the construct load is less,3%; and the influence of the live loads is about 1% of all the datas.4. The shortened statistics of the beam end caused by creep of concrete has the Aging Performance. The creep grows as time goes, and quickly at the beginning, and late slowly, the time is about several years. The influence of the live loads is less, but the shorten caused by temperature change is short. Other factors is not obvious in this part.5. Consider of the prestressing degree, the shortened datas caused by the permanentload and shrinkage cracks of concrete and temperature are constant, while, datas caused by prestressed reinforcement and the creep grow as the prestressing degree grow.6. The cross section stress distribution of the plain concrete and ferroconcrete are similar. Pre-stressed Concrete Structure can be seen as withstanding pre-stressed and exterior load reinforced concrete structure. So, these three kinds of structures may use the similar pattern of shrinkage and creep, and cite rebar ratio influence function in order to consider the effects of reinforcement bar on concrete creep. The bar has the negative effect to the shrinkage and creep.According to the above-mentioned research, we come to the conclusion:The ShiLong bridge, which has been uesd for more than ten years, has mostly completed its gradual changel brought by constriction, and the longitudinal shortening of the girder is nearly invariant,the farther shortening has been limited.