Decoupling of Undamped Vibration Systems

Decoupling of a multimass vibration system from a large structure is investigated. First the dynamic influence on the foundation (or floor) response spectra of the inertia of the subcomponent system is studied using time-history input. Secondly, the affect of coupling on the natural frequencies of both the structure and subcomponent system are studied using formulas developed from normal mode theory. Results of these studies show that equipment-structure interaction cannot be neglected if the subcomponent is in resonance with the structure. The foundation (or floor) response spectra is significantly reduced at original peaks in these curves. Shifts in frequency of the system are also more pronounced at this resonant condition. Estimates of frequency changes of both the structure and subcomponent are related to a ratio of the modal masses of the subcomponent and the mass of the structure.