Calculation and Measure of Web Vertical Stress Field Using Low Retracting Prestressed Anchorage

For calculation of stress field when low retracting prestress stranded tendons system applied in web of box beam,a rectangular plate was fabricated to test the instantaneous prestress loss and vertical prestress fields of different cross-sections of rectangular plate were measured.According to the loading characteristics of web under vertical prestress,the stress of web was solved by the numerical computations based on the theory of the plane stress of elasticity under local vertical load,and the calculation formulas among the dispersion angle of stress,the uniformity of stress and nominal stress was derived by polynomial fitting accordingly.The result of the prestress loss test confirms that(1) the instantaneous prestress loss of the low retracting prestress stranded tendons anchorage is lower than 5%,which demonstrates that the new system used for short tendons can improve the prestress efficiency,and it also can enhance the antishearing capacity of box beam if it is used for the web of box girder.The calculation result based on the elastic theory is in good agreement with that of the experimental test on the stress field of rectangular thin plate prestressed with vertical tendons.The stress level and the evenness of each crosssection can be remained in favorite status when the dispersion angle is smaller than 26.5°,which proves that there is a fine prospect for the application of low retracting prestressed anchorage in vertical prestress system of web.