Vibration Control of Beams by Moment-Type Dynamic Absorber

Dynamic absorbers are widely used for suppressing the vibrations of beam-like structures such as skyscrapers and long bridges due to an earthquake or strong wind. These dynamic absorbers utilize the shearing force that they exert on beam-like structures (they are defined as shearing-type dynamic absorbers). In this paper, the authors propose a new type of dynamic absorber utilizing the bending moment that it exerts on a beam (it is defined as a moment-type dynamic absorber). The frequency responses of a cantilever and simply supported beams to which a moment-type dynamic absorber is attached, and tuning conditions of the dynamic absorber are discussed theoretically and numerically. Trial moment-type dynamic absorbers were made using three-layered sandwich beams and auxiliary masses. The dynamic absorbers, which approximately satisfy the optimum conditions for the first mode of a cantilever and simply supported beams, were attached to the beams, and the effects of vibration suppression of the dynamic absorbers were measured using an electromagnetic vibration machine. The experimental results showed that the moment-type dynamic absorber is more effective than the shearing-type dynamic absorber for suppressing the vibration of the beams. The experimental results were compared with the calculated results, and the propriety of the calculations was confirmed.