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Re: Detailing Question

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One option we've used is to cut the deck around the connection and support it with angles welded to the beam top flanges.  If it's a four-beam connection, the angles will form a diamond shape in plan.
 
Then cover the whole thing with a piece of 20 to 12 gauge flat stock depending on hole size and roof loads.
 
----
Jason Kilgore
Leigh & O'Kane, L.L.C.
jkilgore(--nospam--at)leok.com
(816) 444-3144
----- Original Message -----
Sent: Thursday, January 02, 2003 11:48 AM
Subject: Detailing Question

A question was posted by another engineer on this forum back in May that I was interested in, however, it received no responses that I know of.  Maybe someone could share their experience with this problem if I restate it. 
 
Say you have a sloping roof beam, running parallel to steel joists, with a moment connection with bolted flange plates.  The top flange plate may be an inch thick and the bolt heads and washers add another 3/4" or so.  How do you detail the metal roof deck at this location?
 
Here are some thoughts and problems associated with each:
1:  The roof deck could be bent over the flange plate and bolts producing a ~1 3/4" bump.  The bump in the deck could possibly be compensated by cutting the rigid insulation above.  This could be difficult and depend too much upon the worker's skill.
 
2:  The metal roof deck could be cut around the flange plate and the deck would be supported on the top flange of the beam.  But, is it wise to detail the flange plate to have 3 or 4 inches less width than the beam's top flange?  What could support the roofing where the deck is cut?
 
3:  The direction of the joists could be changed such that the beam with the moment connection would support joists rather the metal deck.  This would provide at least 2 1/2" between the top of steel and the roof deck to allow room for the moment connection.  But, this can cause problems because now the beam becomes a "girder" with a larger moment of inertia required.  When designing a moment connection based on the capacity of the beam (FEMA 350), a larger beam results in a bigger moment connection.  I would also like to keep the span of the joists parallel to the slope of the roof.
 
4:  The beam's elevation could be lowered, and a "spacer" (such as a 4"x4" tube) could be intermittantly welded to the beam's top flange and run the length of the beam.  The spacer would support the roof deck.  At the flange plate, the "toe" of a steel angle could be welded between the two rows of bolts, and the outstanding leg would support the roof deck.  Can you weld anything to the flange plate of a moment connection without affecting the prequalification of the connection?
 
Maybe I've missed the simplest solution of all.  Moment connections for sloping roof beams seem fairly common...surely someone has solved this problem before.  Any thoughts or comments would be appreciated.
 
Thanks,
David Dickey