Application Study On External Prestressing Technology In Existing Bridge Strengthening

External Prestressing is used usually in existing bridge strengthening. The practices in bridge strengthening used external prestressing in the world proved that this technology can keep structure integrality and makes the old structure worked consonantly with the new structure, and the problem of stress-lag while using other strengthening method is avoided. Traffic does not need to be closed, the bridge deflection and crack will be decreased and bridge bearing capacity be increased when using external prestressing method for bridge strengthening.The problem in external prestressing design and construction is study in this paper relying on the Songyuan Songhuajiang bridge strengthening project. Design scheme for external ptrestressing strengthening is determined through theory analysis, and the key construction technology determined through site test. The whole construction process was supervised, and strengthening effect was evaluated through load test after the project completed.1. Songhuajiang bridge was analyzed from construction stage to employ stage according to the design code, and combined with the results of bridge check and load test, the main factors lead to too large deflection and crack is determined.2. According to the results of theory analysis and load test, design scheme for external prestressing strengthening was set down and the tendon arrangement determined, the anchorage and divertion also be designed. The structure bearing capacity using external prestressing strengthening is verified.3. Bearing capacity test of steel anchorage box was carried out to verify the reliability of the anchorage system. Steel bar planting technology was determined through the test of planting steel bar, and the scheme for tendon settling and drawing established.4. Supervising plan was set down for tendon constrction, and the tendon vibration frequency, tendong elongation, steel anchorage distortion, the deflection and crack of the T beam was supervised during construction.5. Strengthening effect was summarized and evaluated through load test after the project completed.