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RE: Garage Floor in Residential House

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My $.02 - I wouldn't rely on it.  You need to prevent twisting of the
compression flange about a longitudinal axis.  If the secondary members were
of steel and attached to the upper 1/3 of the web of the girder, AISC would
consider it braced, but with wood I would be concerned about crushing of the
2x12s before they could develop enough restraint.

	-----Original Message-----
	From:	Rob Quiring [SMTP:robq(--nospam--at)uniserve.com]
	Sent:	Friday, February 05, 1999 12:12 PM
	To:	seaint(--nospam--at)seaint.org
	Subject:	Garage Floor in Residential House

	I have a garage floor that is 21'x21' square, that supports cars and
light trucks (50 psf live load + 60 psf dead load) and is constructed with
2x12 DFir @ 12" o.c. (span 10') flush framed into a steel W14x30 steel
(simple support) beam that spans 21' from front to back at the middle of the
garage.
	 
	a 2x4 is bolted on top of the bottom flange at 36" o.c. each side of
the beam. the 2x12 are framed on top of the 2x4 with blocking every second
space.
	 
	2x4 strapping run perpendicular at 16" o.c. on top of the 2x12 to
allow for venting, with 5/8" plywood, waterproof membrane, and 4" of
concrete on top.
	 
	my problem is that there is a 1/2" gap between the top of the steel
top flange and the plywood floor above providing no lateral support for the
beam at the top flange.
	 
	my Question is: do the 2x12's framed tight against the web of the
beam, which stop 1/2" shy of the bottom of the top flange provide lateral
support for the top flange of the beam when the beam is in compression?
	____________________________________________________
	Rob Quiring
	Isaak Engineering
	Abbotsford, BC