Performance evaluation of vibration-sensitive equipment foundations under ground-transmitted excitation

The planning of foundations for equipment that is sensitive to vibrations requires a thorough dynamic investigation of the proposed location of the foundation with regard to the effect of already existing or additional vibration sources. This paper discusses the analyses performed for a number of foundations supporting vibration-sensitive equipment that has been subjected to ground-transmitted excitations. These analyses considered the dynamic response of the foundations resulting from the normal operation of the supported equipment or the ground-transmitted excitations. In one case, the foundation of the Canadian Light Source, a third generation synchrotron that will be capable of generating electromagnetic radiation used in the study of the atomic and subatomic structure of materials, is examined. Another case involves the vibration analysis of a magnetic resonance imaging unit affected by traffic excitation. In the third case, a power plant facility that is subjected to blast-induced vibration from an adjacent quarry is investigated. The last case involves the response analysis of a compressor foundation affected by the ground-transmitted vibration from another compressor situated on a different foundation within the same facility. To assess the level of seismic excitation at the site due to traffic on an adjacent roadway in the first two cases and to blasting activity in the third case, extensive "green field" ground vibration-monitoring programs were carried out. The ground accelerations due to traffic and blasting were measured and recorded for three directions simultaneously: a vertical and two orthogonal horizontal directions. The measurements with the most intense ground accelerations taken at the ground surface in the location of the future equipment foundation were selected as the final design acceleration time-history. A Fourier analysis approach was used to predict the response of the foundation to the ground-induced vibrations in the first three cases, and a frequency domain analysis was used in the last case.Key words: machine foundations, vibration, blasting, kinematic, soil-structure interaction.