The isolation of vertical vibration is being an insurmountable problem for traditional isolators due to that large stiffness is necessary for supporting upper structures.A new vibration isolation strategy for overcoming this problem based on magnetic levitation semi-active control technique is proposed in this paper

and it has been applied to the semi-active control of bending vibration of a simply supported beam.The governing equation of the semi-active control system for the beam bending vibration is derived on the assumption that beam mass is lumped in the middle of the beam.The system stability at equilibrium points is studied and the extended Runge-Kutta formula is applied to solve the system subjected to random ground excitations.The acceleration response of the system is investigated.The results indicate that the initial suspension position is an equilibrium point of the system and it is L-stable.The magnetic levitation component is similar to a soft-spring device.The vibration frequency of the semi-active control system is lower than that of the common simply supported beam

and the acceleration response is obviously reduced.The system has an excellent quality in the isolation of vertical vibration.