Pratical Method Of Fundamental Frequency For Larhge Span Prestressed Concrete Girder Bridge With High Piers

Nature vibration properties of bridge which is the foundation of all dynamic analysis of the bridge occupies very important position in bridge's dynamic analysis. At present the non-equal beam bridge can get accurate analytic solution, but to variable cross-section beam bridge is mainly on the numerical analysis method to solve. The most commonly used numerical analysis method includes the finite difference method and finite element method. Numerical analysis method can be got more precise analysis results, but it makes against engineering and technical personnel's rapid judgment of bridge structure because of the time-consuming longer. Meanwhile, the main impact to coupled vibration of the bridge is the first vertical vibration frequency. Therefore, this thesis aims to study the nature vibration properties of variable cross-section beam bridge and provides reference for the dynamic analysis of this kind of bridge. The thesis also gives the fast calculation formula of the bridge's fundamental frequency and first vertical vibration frequency to convenient the practical application of engineering and technical personnel. So the research of nature vibration characteristics of variable cross-section of the beam type bridge has important theoretical significance and practical value.In this thesis, based on a variable section continuous beam, continuous rigid frame, and rigid frame- continuous composite bridge project in Shaanxi. The factors is considered, such as the span changes, the number of spans, cross-section size and the number of changes in height and pier section size changes. The various combinations forms of bridges are also considered in the structure for the rigid frame- continuous composite bridge. On the case of above parameters, structural design principles as the theoretical basis and a large number of bridges models, modal analysis and the laws of effect to natural vibration characteristics are carried out. For the variable cross-section beam, the bridge span length, the ratios of spans, cross sectional moment of inertia, ratio of cross sectional inertia moment and area and ratio of pivot inertia moment and area are considered as parameters. For the continuous frame bridge, on the basis of considering the above parameters, the ratios of piers' quality and the main girder's quality and the ratios of piers heights and middle cross-spans are also considered. For rigid frame-continuous composite system, besides the factors of continuous rigid frame bridge, the impact of bridge structure style changes are introduced, too. By the regression analysis, the fundamental frequency formulas of the above three bridges and first vertical vibration frequency are given for the first time, and numerical example is also carried out.The conclusion of the study can be take reference for the design of such bridges and for the subsequent dynamic analysis, and also facilitates the practical application of engineering and technical personnel.