Study On The Factors Which Influence The Pre-stressed Concrete Bridges Cracking And Down-warping

With the quick development of transportation, millions of bridges have been builted in china. The pre-stressed concrete bridges have the advantages of high spanning ability, excellent performance in-service phase.While with the increasing of the service time, a large part of the pre-stressed concrete bridge is emerging cracking and down-warping problems. The cracking is coupled to the down-warping, the coupling has lowered the pre-stressed concrete bridges character of service. How many factors have influenced the pre-stressed concrete bridges crack, how much level do the crack which has been engendered by the many factors influenced the pre-stressed concrete bridges deflection, these problems are not resolved. The paper deliberates how to simplely calculate the midspancross section effective stiffness and deflection, how to evaluateevaluate the important factors which influence the structure cracking and down-warping.This paper, with considering the nonlinear characteristics of concrete and steel bars, studies the cross-section balance equation; meanwhile, the damage stiffness analysis method of pre-stressed concrete beam is presented.The paper has analyzeanalyzed all beam elements' cross-section balance equation,and decreases the cracking beam elements' stiffness. In the end, it calculatecalculates the deflection of the midspan and the Forth under the structure' stiffness, and shows the deflection changeable discipline in the different influenced factors.By means of research, we find the most important factors,which include the increasing load, the loss of prestressing force, the diagonal cracks, the shrinkage and creep. According to the numerical simulation, it researches the four changeable factors which influence the stiffness loss and the deflection increacement. of the simply support T beam and box girder. The increasement of the load and the loss of the prestressing force has the obvious influence to weakenweaken the structure stiffness, when the sections start to crack, the sections stiffness fall down quickly, then tend to keep steady; when the sections stiffness does t fall down, the deflection changes slowly, while the stiness falls down quickly, the deflection has increased sharply with the tend of straight line. In addition to this, the diagonal cracks, the shrinkage and creep also have the influence to the cracking and down-warping, When the midspan stiffness tends to steady, the Forth stiffness begins to weaken quickly, the fall structure stiffness keep falling down. It has proved that the four factors are important to influence the cracking and down-warping of the pre-stressed concrete bridges.