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RE: steel joist design

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The reason that we brace the bottom chord is because the web members will have compression elements.  Any element in compression must be braced in some manner.  Joseph Yura gave a good write up of this some time ago. 

Regards,
Harold Sprague


From: akester(--nospam--at)cfl.rr.com
To: seaint(--nospam--at)seaint.org
Subject: re: steel joist design
Date: Thu, 11 Sep 2008 10:35:15 -0400

Gerald et al,
The first thing I asked them is can we not use an off the shelf channel or WF if they are that desperate on time? It is a mezzanine but it is only spanning 12ft @ 2' o.c. I nearly laughed when they said they already suggested that but the client wants the "look of a steel joist". Now I play amateur architect all of the time, especially with some of the crap I see being built, but that takes the cake... I like exposed structure as much as any engineer, but an exposed 12K1 for your mezzanine is not exactly going to put you on the cover of an Architecture magazine, not even an honorable mention in MSC....
 
So we have decided to design it as a "steel floor truss" and not use a SJI designation. We will put the live and dead loads we designed it for on the drawings, and it will exceed the same table value out of Vulcraft. Then we just follow normal AISC and FBC requirements. There is no big oversight on this project so nobody will care, as long as the EOR approves it. The fabricator has it drawn up already using pipes as webs and angles as chords. The pipe to angle weld looks a bit tricky as a flare groove weld, but this fabricator does some pretty tricky stuff. I am going to put a couple of rows of bottom chord bridging at 1/3 span points, even though it is a floor and I cannot come up with a good reason to brace the tension chord other than it gives me "warm fuzzies" as Scott says.
 
Any input from anyone? Please CC me directly as I am on digest mode. Thanks!
 
Andrew Kester, P.E.
Principal/Project Manager
ADK Structural Engineering, PLLC
1510 E. Colonial Drive, Suite 301
Orlando, FL 32803


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