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RE: UBC 97, Inverted V-bracing

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I am not too familiar with UBC's latest and greatest, but I think the idea
is for the beam to be able to support vertical loads independently from the
braces (should they fail or lose some of their capacity). Also I have heard
that chevron braces are poor performers and not recommended in seismic zone
4. You might want to consider EBF.

Ghassem.

-----Original Message-----
From: Gunnar H. Isleifsson [mailto:gunnarhi(--nospam--at)post4.tele.dk]
Sent: Wednesday, October 06, 1999 12:38 PM
To: seaint(--nospam--at)seaint.org
Subject: UBC 97, Inverted V-bracing


Hello

I am designing a small (11x11x18 ft) "Ordinary concentrically braced steel
frame" according to UBC 97. This frame supports a Fly Ash Filter/Separator
and is located in seismic zone 4 (Taiwan). This is a two level, rectangular
frame where the Filter is placed inside the frame and is supported at
midspan of the top beams. To reduce the beam sections I chose an inverted V
bracing, where the braces connect to the underside of the top beams at the
support points.

UBC97, Chap. 22, Div. IV, 2211.4, Sec. 9.4.a.3., p.2-251 states that:

"A beam intersected by V braces shall be capable of supporting all tributary
dead and live loads assuming the bracing is not present"

Can anyone explain to me what exactly is the meaning of "tributary dead and
live loads", especially the word "tributary" (my dictionary was not very
helpful here).
Does it mean that the top beams have to have flexural strength to carry the
total weight of the filter and its contents, even if I have the braces
supporting the top beams at midspan? If that is the case, is the dead load
to be factored or shall I use characteristic load?

Thanks in advance

Regards
Gunnar Hafsteinn Isleifsson
Struct.Eng.
Denmark