Study On Mechanism And Reinforcement Of Longitudinal Cracking Of Bottom Slab Of PC Box Girder Bridge With Variable Sections

Transportation is the vanguard of economic and social development.Prestressed concrete box girder bridge is widely used in traffic construction with its advantages of large span capacity,good integrity and so on.However,due to various reasons such as design,construction and management,the prestressed concrete box girder bridge at the bottom slab is prone to crack in the construction and operation period.When it is serious,the stability and service life of the bridge will be destroyed,and the maintenance cost will be increased.Domestic and foreign scholars have done a lot of research on the cracking reasons of box girders,but most of them are focused on the research of cracks in the roof of the box girder,while the longitudinal cracks and transverse force analysis of bottom plate are relatively few.Based on the actual engineering,this paper explores the box girder bottom longitudinal cracking mechanism and takes effective preventive measures.Combining theory with finite element analysis,parameter analysis of longitudinal cracking factors of prestressed concrete box floor is carried out,and combined with field test results,the effectiveness of bridge reinforcement is verified.The main work of this paper is as follows:(1)This paper starts with the type,location and origin of cracks in box-section beams,and with the theory of box section,from the aspects of radial force of prestressed tendons,height difference of closure segment,angle effect of prestressed tendons and the setting of the steel bar,the main mechanism of longitudinal cracks in the floor of prestressed concrete box girder bridge and the main factors of vertical cracks in the bottom of box girder under construction and operation conditions are analyzed.(2)Based on the engineering example,the finite element software midas Civil for bridge structure analysis is applied to establish the overall model of the structure analysis.Through the overall structure calculation,the internal force and stress distribution law of the bridge before and after the closure of the bundle and under the status of completed bridge is obtained,and the boundary conditions are provided for the local model analysis.(3)Based on the overall calculation results of midas Civil,the general finite element software ANSYS is applied to build and calculate the solid modeling of the bridge,and the transverse force law of the bottom slab of the box girder is analyzed.By controlling the influence factors of transverse force of box girder at bottom slab,the transverse force of the box girder is analyzed by the parameterized analysis,and the effect of each parameter on the force of the bottom slab is obtained.The results indicate that the frame effect caused by the dead weight of concrete,the radial force generated by longitudinal prestressing of the bottom slab,the time of tensioning of the prestressed steel beam in the bottom slab,the Poisson effect of concrete,the segmental corner effect caused by replacing curve by straight line during construction and other factors have a very important influence on the transverse force of box girder bottom slab.(4)Through analysis of periodic inspection data of the bridge,it was found that longitudinal cracks in the bottom slab of the box girder occurred most.Combined with the design reinforcement scheme,finite element simulation analysis is performed on the reinforced bridges.Based on the comparison analysis of theoretical values of the finite element structure calculation and field load test data,the reinforcement effect of the bridge is evaluated.The results show that the selected reinforcement method is beneficial to the bridge,and prolongs the service life of the bridge,which provides certain reference value for the construction and reinforcement of the same type of bridge.