Research On Shear Lag Of Large-span PC Wide-span Cable-stayed Bridge

The box section was widely used as the main beam structure of modern cable-stayed bridges.Under the condition of space stress,especially the compressive and bending loads,the box girder has its longitudinal stress distribution along the transverse distribution that is not uniform,which is called the shear lag effect.The shear lag effect will cause local stress concentration on the flange of the box girder.This effect cannot be ignored during the design and construction of the bridge structure.Otherwise,the safety reserve performance of the structure will be weakened,and in severe cases,the structure will even be destroyed.Therefore,in this paper,combining with relying on the project,the shear lag effect of long-span wide-width PC double-sided box single-tower cable-stayed bridge is studied,which has practical engineering value and theoretical research significance.This paper adopts the methods of theoretical analysis,numerical simulation and engineering practice to systematically carry out the study of shear lag of a long-span wide-width PC bilateral box single-tower cable-stayed bridge.The main research content is as follows:(1)Based on the method of solving the shear lag effect in box-girder by the Bar Simulation Method,the expression of double-triangle side box girder stiffener's equivalent area was derived.Based on the characteristics,boundary and load conditions of the simply supported double box girder section,using the deduced three-bar analogical differential equation,the shear lag coefficient of the simply supported double-sided box girder under uniform and concentrated loads was calculated.The establishment of a solid model verifies the accuracy of the algorithm.(2)Using the space finite element method,the appropriate unit was selected to establish the model,and the shear lag effect of the double-box main girder roof and bottom floor of the cable-stayed bridge with single tower at the construction stage and the completion stage was calculated and analyzed.The influences of these parameters on the shear lag effect of the main girder are studied by changing the stiffness ratio of beam and tower,the lateral distance of the tower limb,tower cable spacing,and the ratio of tower height to span.The analysis results show that the stiffness ratio of beam and tower and the lateral distance of the tower limb have almost no effect on the shear lag coefficient of the main section of the whole bridge.The parameters that have a major influence on the shear lag coefficient of the main beam are the tower cable spacing,and the ratio of tower height to span.(3)The local solid model was established and the appropriate shear lag coefficient expression was selected to analyze the influence of different design parameters of the main box girder: the thickness of the top plate,the web thickness,and the position of the small stringer on the shear lag effect of the main girder.The analysis shows that the shear lag effect is alleviated with the increase of the thickness of the roof and the web and the spacing of the small longitudinal beams,but the amplitude is weak,and the shear lag effect is less sensitive to the above three factors.