The article presents a method for determining the dynamic characteristics (period and form of natural vibrations) of buildings and structures, taking into account the flexibility of the foundation under seismic impact. This also takes into account the uneven settlement during the construction of structures on various soils. The total displacement of the mass of the structure under seismic effects, taking into account the compliance of the base, is recorded as the sum of displacements from shear and rotation. In addition, a coefficient is introduced into the calculation, which is the mode of vibration of a rigidly embedded system. The formulas obtained can be used to create a mathematical model of the joint work of the "foundation - structure" system.

Keywords: structure, dynamics, natural oscillations, oscillation period, oscillation shape, base pliability, seismic impact