According to the structure and design characteristics of a high strength light-weight continuous rigid- frame bridge, dynamic model for it was established with FEM theory. Contributing ratio of mode shapes, natural frequencies and primary frequency of the bridge were calculated and analyzed with consideration of P-Δ and geometrical non-linearity effect. Conclusions are drawn as follows: (1) At deadweight direction, accumulative contributing ratio convergence speed of mode shapes is slower than that of the common concrete bridge. (2) Fundamental frequency is 13.4% lower than that of the common concrete bridge, and natural frequencies descend on the whole. (3) The first mode shape is longitudinal excursion, which is the same as the common concrete bridge. It indicates that longitudinal stiffness of the bridge is smaller than that of other direction due to great influence of the flexible double thin-walled piers.
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