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RE: Bottom Chord Bracing of Steel Joists in a Hybrid Roof[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: Bottom Chord Bracing of Steel Joists in a Hybrid Roof
- From: "Freeman Tang" <ftang(--nospam--at)gouvisgroup.com>
- Date: Fri, 20 Jan 2006 12:56:27 -0800
- Priority: normal
I think you are right. Although I have not gone through the calculations, like you did, to justify it. The way I look at it is that the bottom chords of these steel joists are most of the time in tension due to gravity loads, and axial loads due lateral load through the diaphragm are mainly along the top chords of joists, girders, and sheathing. These braces are mainly to further stabilize bottom chords of joists. The 2% for compression due to wind uplift should deemed enough
From: Bill Allen
I’m reviewing some shop drawings and I’m having some angst with a bracing detail.
Roof joists are steel joists (Vulcraft)
Roof framing is a panelized wood roof with
The detail shows a single angle running
from the top of the double angle bottom chord and attaching to a sub-pur
I originally rejected this connection
since the sub-pur
The contractor has come back and said that this is a standard connection and they do this all the time, yadda, yadda.
In the interest of having an open mind, I
did verify with Simpson that the F hangers do not have an uplift capacity. I
looked at the joists, took the maximum moment and divided that by the minimum
joist depth and considered 2% of the chord force as the brace force. I admit,
the load is dinky; something like 65 pounds. Considering 8 PSF dead load, the
minimum reaction is still positive (no net uplift) and there is no negative
bending (unbraced length) in the sub pur
Am I missing something?
T. William (Bill) Allen, S.E.
Consulting Structural Engineers
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