A study of power transmissibility for the vibration isolation of coherent vibratory machines on the floor of a building

Vibration isolation is commonly adopted by engineers to reduce the vibratory effect caused by building services equipment. However, the relationship between the amount of sound power transmitted to the floor and the interaction between the mounting points of several machines is uncertain, as it is common to install several coherent machines on the same floor, for example, two water pumps of the same type in a plant room. We conduct an analytical study of the effects of the interaction between two coherent vibratory sources on the power transmitted to the floor. The study is based on two simple vibratory sources with a single contact point, two rectangular machine models of even-mass distribution with four symmetrical supports and the calculated mobilities of a simply supported concrete floor. We find that the total power obtained from coherent sources (point sources or machine models) differs considerably from that obtained from independent sources at some frequencies in a vibration isolation region. To predict the performance of isolators more accurately, the power transmissibility method proposed previously by Mak and Su should consider not only the effect of effective floor mobility and the interactions of the mounting points of the same sources, but also the interactions of the mounting points of different sources on the floor.