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RE: UBC 97, Inverted V-bracing

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"Tributary" means that area that, when loaded, imparts a load on the
structural member in question.  In your application, the "tributary" area is
that area in plan that will impart a gravity load on the member.  

The V brace you describe infers that it is there just for gravity loading.
If your V brace is not part of the lateral force resisting system, then it
has to be checked for deformation compatability.   

In general V braces are used for lateral load resistance.  If the V brace is
part of the lateral load resisting system, the beam must safely span from
end support to end support if the V brace fails.  This means that the load
factors are required.

Harold Sprague
The Neenan Company

-----Original Message-----
From: Gunnar H. Isleifsson [mailto:gunnarhi(--nospam--at)]
Sent: Wednesday, October 06, 1999 1:38 PM
To: seaint(--nospam--at)
Subject: UBC 97, Inverted V-bracing


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

Gunnar Hafsteinn Isleifsson