Influence of rubber sheet on dynamic response of machine foundations

Abstract

In this study, the efficiency of employing rubber sheets to modify the dynamic response of a concrete machine foundation model of size 400 × 400 mm is explored by conducting a series of steady-state vertical vibration tests. Rubber is a low-cost energy dissipater material having high resistance to erosion which can be used in a form of sheets and simply placed beneath foundations. With a lower shear modulus than soil, it is expected to reduce the resonant frequency of a vibrating system but to increase the resonant amplitude. The former is beneficial if moving the resonant frequency far away from the machine’s operating frequency, but the latter is not desirable. To protect the rubber from UV radiation degradation, it may be helpful to embed it in soil. In this study the effects of rubber sheet thickness, vibrating system weight (dead weight), angular dynamic force and embedment depth of rubber sheet were investigated via a series of near-full-scale laboratory tests. It was found that using rubber sheets with thickness of 12 mm can increase the equivalent damping ratio of bed (up to 28%), reduce resonance frequency (by up to 13.6%), decrease transmissibility and contrary to expectations, reduce resonant amplitude (by up to 22%). Nevertheless, the efficiency of employing a rubber sheet to dynamically retrofit machine foundation depends on the angular dynamic force amplitude and dead weight of the vibrating system.