A Study On The Vertical Prestress Action And Its Spacing Of PC Continuous Rigid Frame Bridge

In recent years,with a large number of continuous rigid frame bridges being constructed,the problem of web cracking has gradually emerged.In this paper,the vertical prestressed reinforcement which seriously affects the crack resistance of web is studied.This paper introduces the development of vertical prestressing and the research status at home and abroad,as well as the shortcomings in the research.It mainly studies the effect of vertical prestressing and the distance between vertical prestressing reinforcements.The specific work of this paper includes the following four aspects:(1)Based on the theory of elastic mechanics,the mechanism of vertical prestressing is analyzed,and the necessity of vertical prestressing reinforcement for web to resist the main tensile stress and enhance the shear strength is proved.According to the relevant provisions of the code for vertical prestressing reinforcement,the control measures for the loss of vertical prestressing are obtained.The shortcomings of the study on the spacing of vertical prestressing are put forward,and the most important conclusions are obtained that the small spacing should be controlled by the loss of vertical prestress caused by the elastic compression of concrete,and the maximum spacing should be controlled by the blind area of vertical prestress.(2)Based on the theory of elasticity,the calculation formula of the vertical stress distribution in the web caused by the vertical prestressed reinforcement is deduced,and the correctness of the calculation formula is proved by using the ANSYS finite element modeling;the distribution law of the vertical stress in the web caused by the vertical prestressed reinforcement is analyzed by using the calculation formula of the vertical stress in the web.(3)Based on the theory of prestressed blind,using the calculation formula of vertical stress distribution in web caused by two vertical prestressed reinforcement and the statistical data of Shaanxi continuous rigid frame bridge,the maximum reasonable spacing of vertical prestressed reinforcement should be 0.3177 times of beam height;(4)The formula for calculating the loss of vertical prestress caused by concrete elastic compression is derived.The elastic compression loss rate of vertical prestress is defined by using the formula for calculating the vertical stress distribution in web caused by three vertical prestressed reinforcement,based on the principle that the elastic compression loss rate should not be too large,it is determined that the minimum reasonable spacing of the vertical prestressed reinforcement should be Y times of the beam height,and the value of Y is obtained by a quartic polynomial about the beam height.