In this work, the modal and the forced vibration dynamic analyses are carried out in a railway bridge model. Bridge structure in prestressed concrete is mainly composed by two simply supported I-beams, which are represented with 3D frame finite elements. The Rayleigh’s method is used in structural damping. Rails are modelled with Euler-Bernoulli beam’s. Sleepers and ballasts are modelled with spring-damper systems. Track irregularities are represented by harmonic functions. Mechanic contact between wheels and rails model is based on Hertz, Kalker, Coulomb, Vermeulen and Johnson’s theories. Train composition model is obtained by the 8 vehicle’s association with 25 degrees of freedom each. Modes of vibration are presented alternately between vertical bending, lateral bending, torsional, and longitudinal. Bridge structure presents a over conservative design, which result in small displacements.