Study On Vertical Prestressing Loss And Detection Methods For Prestressed Concrete Box Girder Bridge

The main function of prestressed concrete box girder bridge vertical prestressing tendonsis to provide vertical pre-stress to inhibit the development of principal tensile stress, so as toachieve the purpose of preventing cracking of girder webs. However, there is always crackingof prestressed concrete box girder. This is mainly due to the improper operations and positionerrors in the construction process and system defects. All these factors can cause too largevertical prestressing loss, resulting the lack of vertical prestressing forever. However, thereare still no standard and complete vertical prestressing loss calculation method, and so thatwe cannot make an accurate estimate of vertical prestressing loss. In addition, there are nofast and effective detection methods to detect the actual tensile force. This can also make thatit is diffcult to guarantee the construction quality of vertical prestresssing tendons. For theabove problems, this article focuses on the calculation methods of the vertical prestressingloss and the rapid detection methods for the real effective tensile force. I also make apreliminary study on the new twice-prestressed low-retraction steel strand anchoragesystem.The main research work is as follows:Firstly, considering the practical significance of accurate calculation of vertical prestressloss，this article pay much attention to the studys of the vertical prestressing loss in thecalculateion of the sub-loss theory and calculation method and its influencing factors. Thisarticle rely on a continuous rigid frame bridge in shaanxi province, and set feedthroughpressure sensor in this bridge to collect the vertical prestressing loss data. And then, compareand analysis the measured data with the theoretical data. Finally, determine the magnitude ofthe sub-loss and improve the traditional method.Secondly, for the phenomenon of large vertical prestressing loss and the lack of effectivedetection method I compare several methods of the vertical prestressing loss from the threeaspects of the reliability of results, the versatility of methods and economy. At last, thefrequency detection method is the most suitable to promote in the practical engineering. Ielaborated on the detection principle and calculation icon of frequency detection anddetraction detection method. I improve the previous calculation method to its inadequates and I make a real test on the bridge to verify its rationality. Use this method to detect the actualeffective prestress of vertical prestressing tendons, and compare the test results with thefeedthrough pressure sensor measured results.Finally, compare and analyze the major domestic vertical prestressing anchorage system,focus on the working principle and structural features of the YGM anchorage system, andpoint out the defects and deficiencies of the anchorage system. To the inadequates of thetraditional anchorage system, the bridge institude of Hunan University work with other unitsinvent new twice-prestressed low-retraction steel strand anchorage system used to shortvertical tendons. This article specifically elaborate working principle and structural featuresof the new anchorage system. However, the new anchorage system is still lack of specificconstruction guidance. So, this article details the specific construction of the new anchoragesystem points for attention. At last, I make a simple discussion on the new calculationfeatures of the vertical prestressing losses in the new anchorage system.