This paper proposes the practical evaluation methods for the natural period and the vibration mode in one story steel structures with a roof not considered as rigid. The roof consisting of beams and braces is regarded as one dimensional continuum beam with the elastic supports. The vibration characteristics are solved based on the Rayleigh-Ritz method and summarized with the ratio of two kinds of stiffness and mass ratio. The proposed methods are verified comparing with the finite differential method and applied to the frame analysis for a gymnasium with end planes stiffened by braces.
