Research On The Web’s Work Of The Long-span PC Continuous Rigid Frame Bridge

Since30years of reform and opening up, The box section has been widely used inlong-span continuous beam and continuous rigid frame bridge. During the process of theconstruction and operation of the prestressed concrete box girder bridge, quite a part of thebox girder appear cracks, which the web cracking phenomena are most serious. It’s had anegative impact in the security of the structure, durability of the structure, driving comfortand so on, so the study of the stress of box girder web plate is very necessary. In this paper,the stress state is studied from two aspects of theory analysis and test on the web inconstruction stage and operation stage.(1) Under the plane stress state, determined the influencing factors of web principalstress on the basis of the principal stress calculation formula. Analyzing the sensitivity ofvarious factors on the web principal stress. Analyzing the influence mechanism of principalstress of web under the vertical prestressed, Derived the calculation formula of the verticalprestressed theoretically under the action of a single vertical prestressed reinforcement andwith more, It has a close relationship between the vertical stress of web plate and the size ofthe force, the width of the web, web height and vertical diffusion law.(2) Relying on the liugou bridge, on the web, embedding strain gauge in theupper,middle and lower web, to monitor the stress of web plate in the construction phase,research the stress change rule in different stages of construction on the same point on theweb section. Comparing the measured data and theoretical calculation results, analysis thereasons of the differences, and forward some matters that should be paid attention to inconstruction stage.(3) Based on the research of the method of drawing principal stress line, using wiredapproximation method to draw the principal stress line of long span continuous rigid frame.Check the line’s shape and direction, to verify the necessity of configuration in the web andvertical prestressed reinforcement, which to reduce the principal tensile stress, resist the webcracking. It has positive significance to optimize the web’s reinforcement.(4) Most experts and scholars believe it has significant effect that vertical prestressedreinforcement to improve the web principal stress reserve. This paper focuses on comparisonof the principle tensile stress in the bridge operation stage, in the road of moving loads, whichis to set the vertical reinforcement, vertical reinforcement load design value is50%and not setting up vertical tendons, Concluded that the influence of vertical prestressed reinforcementfor box girder web principle tensile stress.(5) This paper lists several effective measures to improve the web stress state, mainlyfrom the section and the prestressed into consideration. This paper introduces that growth webthickness transition region and add the optimization of frame girder strength sex measures; Atthe same time introduces the vertical prestressed will be tilted and the longer longitudinalprestressed anchorage two effective measures, which can optimize the setting of prestressedreinforcement.In theory, these several methods that can effectively improve the web stressstate, has yet to be validated in the practical engineering design.