Vertical Prestressing Test And Web Diagonal Cracks Control Of PC Box-Girder Bridges

Nowdays, the cantilever construction of prestressed concrete continuous box-girder bridge, which used as the chief constructing method in engineering, has gone to the rang of mature. But the bridges of this type still have some problems. One of problems is concrete cracks on web. Based on the project of the constructing monitoring of the Tianchi Jinshajiang Bridge in Sichuan Yibin city, the site test of the vertical prestressed bars in the box girder web is carried out. By the software analysis results of Bridge-doctor and ANAYS, the thesis mainly discuss the following three issues.1. The origins of diagonal crack on web and the corresponding solved method are studied. Specially, the way of setting the reasonable forms of longitudinal straight tendons, lengthways reflexed tendons and vertical prestressed bars is discussed, in order to prevent the hazardous crack on web.2. Based on the site test of the vertical prestressed bars in the box-girder web, study on the various types of the loss of vertical prestressing in the box girder is carried out. Through the comparison of the measured data with the theoretical data, a reasonable way to calculate the vertical prestressed loss is suggested, which provides reference for the bridge design and construction.3. A new idea of using 'U' form prestressed tendon in web to solve the difficulties of applying and keeping the force of vertical prestressing is presented. Theoretical calculation can prove this idea is feasible in engineering.