The equation of motion of a beam on multiple supports, subject to
prescribed time‐dependent conservative axial loads, is formulated
based on Hamilton’s principle and the assumed mode method. The effects of
sinusoidal perturbations in respect of the axial loads are then examined
using Bolotin’s method. The respective regions of instability are determined
by converting the resulting equations of boundary frequencies into the
standard form of a generalized eigenvalue problem. Instability regions are
presented for various combinations of support configuration, average value
and amplitude of the sinusoidal perturbations of the axial loads.