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RE: controlling vibration on existing steel joist floor

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The first time I saw this as a problem was for a shopping mall designed in the 1960's. The most effective solution then is the same as it is now. Use a tuned mass damper. Back then it was some formed concrete weights suspended by springs. Adding stiffness costs more than it helps.

Today, you can use tuned viscous mass dampers.

There is a program sold by the Steel Joist Institute that you might find handy. The SJI also produces a publication, TECHNICAL DIGEST #5 - VIBRATION, you might find useful.

In my foolish days of youth, I slept on a vibration sensitive pool hall floor, but that is another topic.

Harold Sprague

From: "Pedro Khouri" <khouri_p(--nospam--at)>
Reply-To: <seaint(--nospam--at)>
To: seaint(--nospam--at)
Subject: controlling vibration on existing steel joist floor
Date: Wed, 05 Jan 2005 17:21:32 -0500

(Sory if a repost)

Does any one have recommendation on controlling vibration on existing steel joist floor.

The floor is supporting pool tables in a open room with no partitions.

The floor system is concrete (do not know the thickness) over metal deck supported by 24? deep joist (Vulcraft 11 J 2 per attached tag) spaced at 24? O.C. with a clear span of approximately 48 ft.

The contractor is subjecting the addition of a mid span support with some posts to the room bellow to reduce the joist?s span. I am concern that the added support will negatively affect the joist by inducing negative moments at mid span although the joist members (top / bottom chord & web members) appear to be constant thru the length of the joist.

Any comments will be appreciate.

Thank you,

Pedro Khouri, P.E.

Coral Springs, FL

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