The Stress Analysis Of Twice Tensioned Pre-stressed Anchorage And Concrete Stress Under The Anchorage

At present, the vertical web's pre-stress of the long-span prestressed concrete box-girder bridge is usually achieved through straining steel mills in China. However, steel mill YGM anchor system has so many deficiencies such as great back losses, high-demanding of precision in installation, possibility of pulling off the stell mill, inferiority of the mudjack and so on. To improve that effectively, the Institute of Bridge Engineering in Hunan University, together with Hunan Xiangtan OHM Prestressed Anchorage Company, has developed a "Twice Pre-stressed and Low Retracting Strand Vertical Web in Tension Anchorage System". In order to verify the performance of this new type of anchorage, this paper has made the following researches with the low retracting twice pre-stressed anchorage as subject of study:1. Considing the forces, the conditions in constructing site, and the reliability theory, it is suggested that 25mm is the best length of the nut in this paper.2. The single low retracting twice pre-stressed anchorage nut's maximum stress is at the compressive end contact with the backing plate under the anchor. And the closer to the free end the smaller stress is. At the free end, the axial stress transforms to tensile stress and the hoop stress turns to pressure stress.3. A scaled test of rectangular beam using single low retracting pre-stress anchorage was constructed and experimented. Based on the strain measurements, the stress field under the traditional anchorage and the new low retracting pre-stressing anchorage system are obtained, and the results of the tests are consistent with the theoretical calculation ones. Therefore, compared with the traditional anchorage, the single low retracting pre-stress anchorage has the same contiguration under the anchor.4. Research on actual bridge has been made to measure pre-stress lose of vertical prestressing force in web which low retracting twice pre-stressed anchorage has been adopted. The emphases have been paid to the pre-stress lose induced by compression of joint, deformation and retraction of anchorage, elastic compression of concrete, lose through creep and shrinkage of concrete. And analysis has been made to study the factors influencing pre-stress lose.At last, this paper has put forward some advices and noticable problems for the new low retracting twice pre-stressed anchorage's further development.