Design methods for transient response and isolation of ground-founded microprecision slabs.

Abstract

Design methods and typical case histories are presented for both transient response and isolation problems for ground-founded microprecision slabs. The complexities of transient analysis for test slabs on soil have long been recognized, but until recently such an analysis could be approximated only by using steady-state assumptions. It is now possible to make a meaningful engineering analysis of a transiently loaded foundation on soil by the graphical phase-plane method. The older steady-state approximation may be very unsafe for cases where the input frequency is greater than the natural slab frequency. Increasingly stringent isolation requirements for microprecision slabs, combined with the need to use convenient but often very noisy slab sites, require not only properly designed solid slabs, but also special techniques such as subsurface energy barriers and hollowed slabs. The state of the art in energy-barrie r technology is described for both cutoff trenches and sheet pile walls. It is shown that the energy barriers should extend to a depth of at least one-third the Rayleigh wavelength of the incoming vibrations in order to be effective.