Vibration Isolated Foundations for Boiler Feedpumps


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Title: Vibration Isolated Foundations for Boiler Feedpumps

Author(s): Herbert A. Franklin

Publication: Special Publication

Volume: 78


Appears on pages(s): 161-175

Keywords: concrete blocks; concrete construction; floors; foundations; machine bases; prestressed concrete; structural design; vibration isolators.

Date: 1/1/1982

This paper describes the design and construction of low-tuned, spring supported foundations for boiler feedpumps units installed in the Big Stone coal-fired power plant in South Dakota. Each system consists of a variable speed 9,500 HP (7084 Kw) steam turbine which drives a pair of feedpumps and is mounted on a prestressed concrete inertia block set on steel springs. This vibration isolation design required dynamic analysis of the inertia block systems since the variable speed pumps could present a range of forcing frequencies and hence a series of possible resonances. The concrete inertia blocks were prestressed in order to prevent cracking which could cause significant changes in the dynamic behavior. The concrete inertia blocks were fabricated and prestressed outside the turbine building. Each weighed about 96 tons (854 kN) and they were lifted into position on their steel springs on the operating floor level. The flexible isolation of the inertia blocks from the building floor facilitated the alignment of the machinery and the attachment of the piping. Vibration tests were conducted during plant start-up in order to anticipate potential problems and to verify dynamic characteristics. These units have now performed successfully for several years.