The Study On Stress Calculation Method Of The Design Of Long-span Prestressed Concrete Continuous Box Girder Bridge

Because of the advantages on reasonable stress and convenient construction, the prestressed concrete box girder bridge has been in the majority of China s already built medium and long-span bridges. The recent years bridge surveys show that different degrees of cracking occur in the most under-construction or already constructed bridges, which seriously threaten the safety and durability of the bridges, therefore, it is necessary to probe into the reasons for box girder cracks. Taking a real project as the basis,this paper makes a research on stress calculation method of the design of long-span prestressed concrete continuous box girder bridges constructed in the method of cantilever.The main contents include the following sections:(1) Through the collection of research materials at home and abroad, we make an overview on the development of prestressed concrete box girder bridges and the reasons for cracking phenomenon occurrs in box girder bridges, generalize and summarize the research by the current Chinese scholars on the spatial stress analysis of box girders. And we ve found the design deficiencies in adopting elementary beam theory to calculate the section stress for long-span prestressed concrete box girder bridges constructed in the method of cantilever, and put forward the research direction of this paper.(2) We make a brief overview on the finite element method theory, and through finite element analysis, we study the problems occurred in the process of box girder spatial modeling, such as units selection, meshing, boundary conditions, and simulation of prestressed tendons,etc.(3) To make cantilever beam for simple rectangular cross-section, analyse and calculate in the case of local compression stress state, on this basis, using finite element model of solid element to make further study on normal stress distribution along the beam axis direction of the cantilever box girder in anchorage zone of top slab tendons and upper and lower edges of the cross-section, and make a comparison with stress calculation results of the beam element,then we put forward the concept of increase coefficient of longitudinal normal stress.(4) We study the influence of geometrical factors of the box girder cross-section on theincrease coefficient of longitudinal normal stress, and fit a relation between the increase coefficient of longitudinal normal stress and geometrical dimensions of the cross-section according to the data calculated from model analysis. In this way, we further propose an amended calculation method of adopting beam element to calculate the normal stress on top and bottom plate of cantilever box girder.(5) Through a specific engineering project, we verify the practicality of proposed calculation method of adopting beam element to calculate the normal stress of cross-section for long-span prestressed concrete box girder bridges.