“…Up to now, the assumed mode method using the characteristic polynomials of the Timoshenko beam (Chung et al, 1993) is successfully applied to the dry vibration analysis of rectangular plates and stiffened panels with arbitrary boundary conditions (Kim et al, 2012;Cho et al, 2013Cho et al, , 2014Cho et al, , 2015. This concept very similar the Rayleigh-Ritz method (Liew et al, 1995), but instead of minimizing the energy functional, it opts to apply Lagrange's equation of motion.…”