Analysis Of Vibration Frequency And Impact Effect Of Prestressed Continuous Steel Box Girder

Steel bridges have the advantages of light weight,high strength,long service life and environmental protection.In recent years,China’s iron and steel industry has excessive capacity.Environmental problems also put forward higher requirements for the civil industry.In the coming decades,steel bridges will usher in greater development.Prestressed steel bridges combined with prestressing force will usher in new development as a reasonable structural form.Continuous girder is an important bridge type in bridge construction.It has large clearance under the bridge,saves materials,and has large stiffness,good integrity,large overloading capacity,high safety,less expansion joints on the bridge deck.Moreover,because the bending moment of the mid-span section decreases,the bridge span can be increased.Based on the model test and modal analysis of three-span prestressed continuous steel box girder model,this paper discusses the factors affecting the natural frequency of three-span prestressed continuous steel box girder,and further analyses the dynamic impact effect of the girder under different span ratios and different leveling conditions.The main research results are as follows:(1)The modal analysis results obtained by the finite element model are basically consistent with the natural frequencies obtained by the modal test.The influence of the tension,the added mass and the span ratio of the prestressing tendons on the natural frequencies of the three-span prestressed continuous steel box girder is analyzed by the finite element model.(2)Through the finite element analysis of coupled vibration,it is found that the change of prestressing force has little effect on the fundamental frequency of three-span prestressed continuous steel box girder,but the ratio of side to mid-span has a greater influence on the fundamental frequency of three-span prestressed continuous steel box girder,and has a greater impact on its dynamic effect.(3)The change of pavement smoothness grade has significant influence on the dynamic effect of three-span prestressed continuous steel box girder,especially for the mid-span section with 3:4 side-to-mid-span ratio,the dynamic impact coefficients of different grade pavement are quite different,which should be considered in the design process.By comparing the impact coefficients of this beam under different side-to-mid-span ratios calculated in the General Specification for Highway Bridge and Culvert Design(2015),it is proved that it is safe to design with the normative formula.