The transverse vibrations of a two-span beam bridge, the shore supports of which interact with the surrounding soil during seismic action, are considered. The condition is accepted that the deformations of structures do not go beyond the limits of elasticity and vibrations are linear in nature. The bridge supports are assumed to be submerged in the ground and interacting with a rigid body under the action of non-stationary dynamic influences. The case is considered when the left, middle and right supports have equal masses and interact with the surrounding soil in the same way. The symmetry condition is applied, and it is sufficient to consider the equation of the right half of the beam. The problems are solved by the analytical Fourier method under the given boundary conditions. The results obtained are presented in the form of stress distribution over time and length of bridge structures, and their analysis is also presented.