To: "'SEAINT(--nospam--at)SEAINT.ORG'" <SEAINT(--nospam--at)seaint.org>
Subject: Balcony Floor Vibration
From: Steve Kramer <s_kramer(--nospam--at)ntda.com>
Date: Fri, 25 May 2001 14:53:42 -0400
I have a balcony with a 28 foot cantilever. The backspan varies from 30 to
45 feet. I'm trying to design for floor vibrations per AISC design guide
11. The balcony is for a church, and my thinking is that my natural
frequency should be at least 6 based on chapter 5 and my peak acceleration
should be less than 0.5% g based on chapter 4.
The problem is that this requires enormous beams, something like W36x230 at
5 feet on center just to get in the ballpark, way more than required for
strength. The problem seems to be the large deflection I calculate for the
cantilever, that results in a very low natural frequency.
Has anyone run into anything similar? Maybe I could use the deflection at
some point other than the end of the cantilever. Maybe 3/4 or 2/3 the
cantilever length, although even this doesn't help as much as you might
expect. Past experience I have had with this design guide is that almost
any floor I check doesn't work.
Any advice or comments would be appreciated.
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