Study About The Control Of Construction Quality For The Tension Of Vertical Prestressing Bars In The Webs Of Long-Span PC Girder Bridges

With the development of bridge construction, prestressed concrete continuous rigid-framed box girder bridges have been widely constructed for its characteristics of higher stiffness, smooth pavement, less expansion joint and low maintenance costs. In recent years, this kind of bridge disease is more and more reported for web cracking. The main reason of web cracking is excessive vertical prestressing force or vertical prestressing force failure. Improving the quality of tensioning vertical tendons is an important measure to prevent web from cracking. Based on the vertical vibration test method to detect the prestressed tendon tension as the main method of quality control, achieved some research, studies on the job and the results are as follows,1,Exposed tendons in the vertical section as the beam model is proposed based on the vertical tendons elastic support model and the space plane elastic support model, elastic support model not only can simulate the vertical section of prestressed beam model exposed bending rigidity, but also can simulate the longitudinal elastic stiffness. Cantilever model by detecting the frequency of the exposed section of the model calculated vertical stiffness of tendons anchoring end of K, the calibration test by K-T, the built-in cantilever beam model of the instrument can be directly calculated by the frequency of detected Tension T value. Combination with engineering test data, flexible support model the relationship between K and T model with the original cantilever relationship between K and T, consistent and flexible support model for the calculation formula is more simple, clear concepts and more conducive to the promotion.2,The sensor calibration test and elongation test on the basis of calibration, calibration tests presented back to the shrinkage method, the calibration test and engineering test data how to do a comparative analysis and research, back to the shrinkage method for its operation simple, accurate, and reliable test data is more suitable for promotion.3,The vibration method of the vertical tensioning tendons and construction process control testing a combination of both vertical tendons quality control measures, control measures on two technical points made a systematic analysis. Engineering practice shows that the vertical in the application of quality control measures tendon, the vertical tendons quality has been markedly improved, is an effective, comprehensive, systematic quality control of construction of vertical tendons way.