Abstract The influence of compressive forces on the lower and upper natural frequencies double beams has been studied in this article. Euler–Bernoulli’s hypotheses have used to derive frequency equations. Two asymmetric were assumed work, four different boundary conditions applied these equations: Pinned–Pinned, Clamped–Clamped, Clamped–Free, Clamped–Pinned. When axial force is increased about ...