Analysis And Treatment Of Transverse Cracks In Continuous Box Girder Bridge Of Heavy-haul Railway

The development of heavy-duty railways is inseparable from bridges.Prestressed concrete continuous box girder bridges are widely used in the construction of heavy-duty railway bridges due to their large structural stiffiness,good mechanical performance and strong seismic capacity.However,with the continuous increase of axle load and traffic volume of heavy-duty trains,many box girder bridges have different degrees of cracks in the operation process,which affects the durability and safety of the structure.Therefore,a scientific assessment of the actual state of the structure after the crack must be carried out in order to select an appropriate repair reinforcement method.At present,there are few studies on the condition of box girder after cracking at home and abroad.In this paper,a super-large bridge of Menghua Heavy Load Railway is taken as the research object.The causes of transverse cracking of box girder are analyzed emphatically,and the changing rules of structural stress and deflection under different cracking conditions are discussed.The main research contents are as follows:(1)On the basis of reading a large amount of literature,the characteristics of concrete materials are summarized.From the properties of concrete itself,the formation mechanism of cracks in box girder is discussed.According to the position of cracks,the cracks of box girder are classified,and the causes of cracks in box girder bridges are expounded.(2)The fracture model,the constitutive relationship and the method of fracture simulation are systematically studied in the finite element analysis,which provides a theoretical basis for the later modeling and calculation.(3)Using Midas Civil to establish a finite element analysis model of box girder bridge,the two factors of temperature and longitudinal prestress are selected to analyze the structure.It is concluded that the temperature load has a great influence on the internal force of the box girder spanning the middle plate.The stress loss has a great influence on the internal force of the top plate near the support and the bottom plate near the middle and side spans.(4)The solid element models of box girder bridges under different cracking conditions are constructed by Midas FEA software,and the effects of statistical parameters of different crack characteristics on the maximum stress and deflection of the structure are explored.The results show that the crack width has the greatest influence on the stress and deflection of box girder bridge structure,while the crack height and the number of cracks have relatively small influence on the stress and deflection of the structure,and the influence degree of the latter two on the structure is basically the same.(5)This paper introduces the treatment principles and common repair methods of cracks in box girder bridges,and puts forward measures and suggestions to improve the durability of bridges from aspects of design,construction and maintenance,hoping to provide some reference for future maintenance and reinforcement projects.