To: "SEAOC Newsletter" <seaint(--nospam--at)seaint.org>
Subject: Re: Equipment vibrations
From: Christopher Wright <chrisw(--nospam--at)skypoint.com>
Date: Mon, 21 May 01 14:11:31 -0500
>Equipment is a new 500 HP electric motor hung below a steel framed free
>standing platform with a concrete deck.
It's not clear what the problem is--that is, what you're expected to fix.
I gather someone's noticed that the platform shakes when the motor runs.
I guess I'd start by finding whether the culprit is the motor or what
ever the motor is driving. If it happens when only the motor runs there's
your culprit. If everything needs to be turning, and the motor's OK it's
in the machinery. You can look for a bent shaft by turning over the
system slowly and checking the runout. If there's an imbalance in
anything that's turning, it won't show up as a deformation. What happens
in that case depends on the location of the machinery with respect to
some soft point in the structure. Probably the best solution is to try to
find exactly what's vibrating and stiffen that. If the motor is mounted
on a soft floor it'll vibrate when the rotational frequency matches the
corresponding frequency. Or the motor may be exciting some other point.
>From what you've mentioned, my first guess is that the motor is mounted
to a soft floor. Sounds a little like a re-fit--someone adding machinery
after the building was built. Try jumping near the motor and get an idea
of the floor frequency. Then run up the motor and see where you get the
resonance. If you find to imbalance in the motor, you'll probably end up
stiffening the floor. Make sure you aren't adding mass at the same rate
as you're adding stiffness, o rit won't do much good.
Christopher Wright P.E. |"They couldn't hit an elephant from
chrisw(--nospam--at)skypoint.com | this distance" (last words of Gen.
___________________________| John Sedgwick, Spotsylvania 1864)
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