Research On Analysis Method Of Multi-cell Concrete Box Girder Bridge Based On Grillage Method

Single-box multi-cell concrete box girder bridges have become the main structural form of small and medium-span bridges due to their good mechanical performance and construction applicability.With the increase in the width of bridge construction,the width and number of box cells of multi-cell box girder continue to increase.Compared with the single-box single-cell box girder,the single-box multi-cell box girder bridge not only resists the external load with the entire section,but also has the lateral distribution effect of internal force similar to the multi-girder structure.As the main design method of multi-cell box girder,the grillage method can effectively simulate the spatial force characteris tics of the structure,but its scope of application needs further discussion.Therefore,this paper takes the single-box multi-cell concrete box girder bridge as the research object,and takes the spatial force characteristics of the multi-cell box girder and the application of the grillage method as the main research points.Based on its structural response under local eccentric load,,relevant discussions are carried out.The main tasks are as follows:(1)Review and summarize the basic theory and grillage division principle of the beam grillage method,and derive the value of the section stiffness of the beam grillage method.(2)Based on the solid unit model,the lateral distribution effect of bending moment and shear force of multi-cell box girder under local eccentric load is studied,and the lateral distribution law of bendi ng moment and shear force under different box width and number of boxes is analyzed.The reason for the inconsistency of the lateral distribution effect of bending moment and shear force of multi-cell box girder is discussed.(3)By changing the width and number of box rooms,the calculation accuracy of grillage method is analyzed.It is found that the grillage method c an better simulate the transverse distribution effect of internal force of multi-cell box girder.Except for the modification of bending moment o f side webs when side webs are loaded,the calculation accuracy of internal force of grillage method meets the design requirements.Based on the sensitivity analysis of the stiffness of the virtual beam,it is found that the bending stiffness and shear area of the virtual beam have a great influence on the lateral distribution of internal forces,and it is further discussed.(4)The stress calculation accuracy of the grillage model was analyzed,and the shear lag coefficient of the multi-cell box girder under different loading methods is calculated based on the solid element model and specificat ions.The results show that the calculation accuracy of the normal stress analysis results of the grillage method considering the shear lag effect can meet the design requirements.Under local eccentric load,the shear lag coefficient of the loading side web is larger than that calculated according to the specifications.The calculation accuracy of the shear stress analysis results of the grillage method meets the design requirements.(5)Through the exploration of the lateral effect of the longitudinal prestressed steel strands of the multi-cell box girder,it is found that the sudden change of the cross-sectional size near the beam end and the pier top and the flat bending of the steel strands near the beam end have no significant effect on the transverse force of the box girder.Suggestions are given for the arrangement of prestressed steel strands in the grillage method model.