Local Stress Analysis And Repair On Bottom Crack Of Prestressed Concrete Box Girder Bridge

Prestressed Concrete(PC) box girder bridge,with good structural characteristics and mechanical performance,has been widely used in highway and railway bridges.With the development of PC box girder bridge,bridge diseases are also accompanied by. In the traffic operation stages,or even in the process of tensioning the prestressing tendons, bottom concrete of box girder bridge appears crack or split, which will delay the construction schedule and seriously affect safety, durability and economy of the structure.Throughout the domestic or foreign accident cases of box girder bridge, bottom cracking phenomenon often occurs, worthy of attention in theory and engineering sessions. In this paper,the bottom cracking case of a prestressed concrete box girder bridge in Guangxi is taken as the engineering background.Through the analysis of the local stress distribution, this paper analyzes the reasons of bottom split in box girder.The research task in this thesis are mainly as follows:1.On the basis of reading lots of literatures, the overview of development,structural characteristics, mechanical performance and analysis method of PC box girder bridge are briefly introduced.And the basic failure modes and integrated control measures of bottom crack in PC box girder bridge are also summarized.And, the preliminary and qualitative analysis of the engineering background thows that the reason for the bottom crack maybe the radial force caused by the deviation of the bottom prestressing tendons.2.Then,this article focuses on the finite element analysis theory of box girder bridge.And based on the Saint Venant principle,the influence of the boundary conditions on local stress distribution is analyzed,when the equivalent force boundary conditions is exerted on the local entity model of box girder. At a distance of0.20B～0.25B (B for box girder width) from the equivalent force boundary, the influence on stress distribution can be ignored.3.With the overall-local model analysis scheme and the establishment of Midas overall frame model and Ansys local entity model,this article comparatively analyzes the local stress distribution in box girder bottom crack under various conditions, verifying the reason for bottom cracking in the preliminary and qualitative analysis,which is the radial force caused by the deviation of the bottom prestressing tendons.4.Static load test is carried out on the bridge after repair, verifying the good effect of repairing of bottom crack in box girder.Then,based on the load test results, a suggestion that tensioning the spare tendons to compensate for the prestressing loss in the bottom of box girder is proposed.