Assessment of the stability of isolated vibratory building services systems and the use of inertia blocks

Inertia blocks are commonly used by engineers to stabilize vibration-isolated building services equipment. However, no comprehensive guidelines for the selection of inertia blocks or indices for assessing the effect of inertia blocks on the stability of the vibratory system are available. In this paper, the level of "power transmissibility" is used to assess the performance of vibration isolators, and the level of the "vibration velocity transmissibility" of the supporting floor structure, the "mounted vibration velocity", and the "mounted rotational velocity level" of the vibratory machine are proposed to assess the stability of the vibratory system with various inertia blocks. The results primarily indicate that the use of an inertia block does not affect the performance of vibration isolation. Instead, it decreases the vibration velocity and rotational velocity of the isolated vibratory machine; so it can increase the stability of the vibratory system regardless of whether the machine has slightly or highly uneven mass distribution. The results reveal that, for the machine with highly uneven mass distribution, the degree of an larger inertia block is required to enhance the stability of the isolated vibratory system. Therefore, in addition to proposing indices for assessing the stability of the vibratory system, this paper also provides an insight into the selection of the inertia block based on the mass distribution of an isolated vibratory machine.