Design of floating floors, suitable for supporting vibration sensitive equipment, in industrial plants

Abstract

The installation of modern sensitive equipment in industrial plants, where high vibration levels are usual, is becoming ncreasingly frequent. Appropriate mountings are required to satisfy the specifications of the equipment manufacturer with respect to the maximal to lerated limits. An alternative solution to the elastic mounting of individual equipment, is the onstruction of isolated surfaces or floating floors, which provides greater flexibility in the layout. Simplified models of one degree of freedom are frequently used for the design of floating floors, disregarding the influence of flexural flexibility of the slabs and the contribution of flexional modes to the response. A rigid base excitation is also a simplification compared with the real excitation consisting of wave trains propagated by the base area where spring elements are support ed. The present paper deals with the investigation of the dynamic response of floating floors excited through the isolation ystem by Rayleigh waves, which propagate in the homogeneous half-space of soil, taking also into account the flexibility of the slabs. The effectiveness of isolation is quantified from the slab maximum displacement calculated in the frequency domain for an excitation with bandwidth within the range of interest of typical commercial equipment. The analysis begins analytically calculating the transmissibility of beams, from which the concepts of modal transmissibility and envelope modal transmissibility are derived. These parameters coming from a one dimensional structure are suitable to be used as a reference in the design of industrial floating slabs. Based on an example of a typical floating floor of a metrology room, we compare results obtained with a finite element model with those provided by the equivalent beam model proposed in this article.