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RE: Framing Decisions

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	Michael,

	I recently worked on a conceptual building design which had a
similar framing concept.  My roof joists were on a 2:12 slope and were
REALLY not vertical.  Again, the joists were not sloping along their
length, but were tilted.  I've seen this done on other buildings, but
have not done it myself.  It looked sort of unusual so I called
Vulcraft.  The individual at Vulcraft said its not a problem to have the
joists tilted, as long as the bridging is tied together at the top of
the building.  This keeps the joists from rotating (back to where they
want to be due to gravity forces).  I felt a little uneasy with the
whole thing, and only let it go because it was a conceptual design for
long term planning/estimating purposes.  Also, there would be minimal
ME&P on the inside, and no roof top units.  This arrangement with any
kind of substantial roof loads probably would not work.

	Sincerely,  Michael D. Ritter, PE



> Michael Zaitz wrote: 
> 
> 	 Hello, I have a warehouse building approximately 500' by 320'
> in dimension.  It is steel framed with joists, girders and tube
> columns, metal deck,  and precast wall panels.  It is a double sloped
> roof 1/4:12 with the ridge running parallel to the 500' dimension. 
> The standard bay size is 40' x 40' with the end bay being 40' x 20'. 
> Due to the length of the building I am putting in an expansion joint
> midway down the 500' dimension across the 320' direction.  At present
> I am running the joist girders parallel to the 320' dimension to give
> me frame action for the longitudinal direction.  For the transverse
> direction I am planning on using the panels as shear walls.  Due to
> the expansion joint I decided to run the girders as I did and that
> solves any stability problems with the frames at the expansion
> joint. Here is the problem.  By running the joist girders the way I
> am, the joists will not be vertical.  With the 1/4 in 12 slope and a
> 24" joist the bottom chord will be 1/2" out of plumb.  Will the joist
> manufacturer design for this?  Or can the joist manufacturer slope the
> top chord to allow the joists to hang vertically and still allow the
> metal deck to get its required bearing?  Will there be gnashing of
> teeth trying to do it this way?  On a similar project that the
> architect was involved in (smaller and not needing an expansion
> joint)  the engineer ran the joist girders parallel to the long
> direction which allowed the joists to slope normally.  I can not use
> x-bracing to get any stability (owner's request) therefore if I run
> the girders in the opposite direction I will need to do a portal
> frame. On a separate issue is there any problem using a precast panel
> in a seismic zone 2 (Av and Aa of 0.18)?
> 
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