“…Some papers studied the free vibration of rectangular plates with elastic/rigid point-supports, based on the energy method, using different approaches such as spline finite strip method (Fan and Cheung, 1984), finite layer method (Zhou et al, 2000), the Lagrangian multiplier (Kim and Dickinson, 1987), the static beam functions (Cheung and Zhou, 1999;Zhou, 2002), the orthogonal polynomials (Liew et al, 1994) and the exact solution (Gershgorin, 1933;Bergman et al, 1993;Zhou and Ji, submitted for publication). Moreover, some papers studied the free vibration of rectangular plates with elastic/rigid concentrated masses by using different methods such as the exact solution (Bergman et al, 1993;Li, 2001Li, , 2003Zhou and Ji, submitted for publication), the optimal Rayleigh-Ritz method (Avalos et al, 1994) and the mode expansion method (Avalos et al, 1993;Wu and Luo, 1997;Wu et al, 2003;Chiba and Sugimoto, 2003). Keane (1996, 1997) investigated the possibility of using attached masses to control the vibration of rectangular plates.…”