This paper describes investigation regarding earthquake-resistant characteristics of mechanical structures that have high natural frequency from a viewpoint of the energy balance. In earthquake-resistant design of a mechanical structure installed in a nuclear power plant, those mechanical structures are basically considered the rigid body and static seismic design is implemented. When vertical component of an seismic wave is considered, floor response acceleration at high natural frequency band is high, and it is expected that excessive inertia force operate against the mechanical structure in design phase. Therefore designing those mechanical structures is so difficult that accurate grasp regarding vibration characteristics, the main cause of fracture and establishment of evaluation technique are required. In this study, earthquake resistant characteristics of mechanical structures that have high natural frequency are investigated from a viewpoint of the energy balance that is one of valid methods for structural calculation. At first, forced vibration experiments were executed in order to confirm differences of input energy between low natural frequency models and high natural frequency models. Then continuous vibration experiments that induce experimental model to fatigue fracture were carried out. Results of these experiments and fracture phenomena were evaluated from the viewpoint of the energy balance.

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