Research On Effective Pre-stress Of The Prestressed Concrete Beam Bridge In Curving Hole

Owing to many natural or artificial factors, such as design, construction, heavy load, temperature and materials, lots of bridges in operation have appeared different types of structure diseases, such as excessive midspan sag, longitudinal cracks in box girder, web's inclined crack and local injury, which are seriously harmful to the operation safety and the lifecycle of bridges. Although the cause has some relation with construction operation, yet the major factor should be due to deficiency of the theory and imperfect design of the prestressed steel. My paper will illustrate the contact-stress distribution between concrete and prestressed steel in curving hole with theoretical analysis and experimental study.First of all, the paper state the concepts of prestressed concrete structure, the history of prestressed concrete bridge and development status of prestressed concrete BridgesBased on Hertz Contact Theory, Several contact stress distributions in Curving Hole are hypothesized and the prestress loss caused by friction was compared with each other. This paper point out that the prestress friction loss of discontinuous Curving Hole can be not equal to the prestress friction loss of continuous Curving Hole with the same tangent angle.According to finite element method, this paper establishes plane finite element model. It shows that contact stress between prestress tendon and Curving Hole present the tendency that largest value is in the middle and the smallest value in two ends.Two experiments has been carried out to detect the variation of the box grider and prestressed steel when the steel's location and tensile force changes. And the prestressed distribution could be got. Using CT scanning technology, the paper discusses the alteration of contact stress distribution with the changes of bend radius and angle.In conclusion, the results are got as follows:①the contact stress between prestress tendon and Curving Hole present the tendency that largest value is in the middle and the smallest value in two ends.；②the contact stress augments with the diminution of the radius, and then attention should be paid to ensure that the bend radius isn't that small;③the bend angle's variation has little effect on the contact stress, but its increase may lead to high stress block and finally magnify the prestressing loss.