Variable stiffness system for semi-active vibration control by frequency

Seismic waves close to the resonant frequency of a structure cause the structure to exhibit large vibrations. The resonant frequency of the structure is determined by the value of stiffness (spring constant). As a method to shift the resonance frequency, the dynamic absorber using additional mass is well known; however, its performance is restrictive. A semi-active control is proposed by varying the stiffness, on the basis of the frequency, to shift the resonant frequency of the structure from that produced by the earthquake. Damping the effect of the semi-active control was verified by simulations and experiments using some seismic waves.