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RE: Steel Moment Frame - Channel to TS Column - FR or PR Connecti on?

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Mark-
Section B9. END RESTRAINT of the "Specification for Structural Steel
Buildings, Allowable Stress Design and Plastic Design, June 1, 1989, with
Commentary" as referred to in Section 2208 of the 1997 UBC reads:

"When designed on the assumption of full or partial end restraint due to
continuous, semi-continuous or cantilever action, the beams, girders and
trusses, as well as the sections of the members to which they connect, shall
be designed to carry the shears and moments so introduced, as well as all
other forces, without exceeding at any point the unit stresses prescribed in
Chapters D through F, except that some non-elastic but self limiting
deformation of a part of the connection is permitted when this is essential
to avoid overstressing of fasteners."

LRFD Volume II- Connections, at pg. 9-234 provides a simplified method of
considering PR connections.  Remember, these will introduce additional
flexibility to the frame which may result in the exceedance of drift
requirements.

The designer must exercise some judgement as to how the rigidity of the
connection will be assured.  I would be careful assuming that a
non-symmetric section, such as a channel, would reliably develop the full
plastic moment capacity of the member in a stress-reversing environment.
Buckling would be a major concern.  Also, I think flexibility introduced by
plate bending, such as your cases 1,2 and 3 where the moment must be
transferred to the webs of the TS via bending of the TS flanges, would be
difficult to determine short of testing the connection.  Whether a
connection is fully or partially restrained is more important to vertical
load behavior than lateral because the joint must develop the strength of
the member at the joint under section 2213.4.2 to be used for seismic loads.


Regards,
Bill Cain, S.E.
Oakland  CA

	-----Original Message-----
	From:	Swingle, Mark [SMTP:Mark.Swingle(--nospam--at)dgs.ca.gov]
	Sent:	Monday, January 24, 2000 9:33 AM
	To:	'seaint(--nospam--at)seaint.org'
	Cc:	'mswingle(--nospam--at)earthlink.net'
	Subject:	Steel Moment Frame - Channel to TS Column - FR or PR
Connection?

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	----------------------------------------------------------------

	Please consider the following examples.  These are beam-column
	moment connections, all of which consist of a channel section
	as the beam, and a TS as the column (1/4" thickness).  All are
	welded connections with no stiffener plates or continuity plates
	at the column.

	I am trying to determine whether each of the following
	connections are judged to be FR (fully restrained) or PR
	(partially restrained).

	1.  An A36 channel, narrower than the TS, welded with CP groove
	    welds at both flanges, and fillet weld (one or both sides)
	    at the web.

	2.  Same as 1., except the flange welds are fillet welds both sides.

	3.  Same as 1., except the flange welds are fillet welds one side.

	-------------------------------------------------

	4.  An A570 Gr 45 channel, 10 gage (with stiffened flange), same
	    width as the TS, welded with CP groove welds at both flanges,
	    and a flare bevel groove weld at the web.

	5.  Same as 4., except the flange welds are fillet welds both sides.

	6.  Same as 4., except the flange welds are fillet welds one side.

	-------------------------------------------------

	7.  Similar to 4., except the flanges are coped and the web
	    continues to the far side of the column.  The web "extension"
	    is welded horizontally to the column (T&B) with fillet welds,
	    and the web is welded vertically to the column at the inside
	    corner with a flare bevel groove weld.

	8.  Same as 7, except with flange welds per 5.

	9.  Same as 7, except with flange welds per 6.

	-------------------------------------------------

	Per UBC 2213.6 (OMF Requirements) the determination of whether
	these connections are judged to be FR or PR is critical to the
	analysis.

	If they are judged to be FR, then they may be designed by
	calculation only with an omega factor on the typical design
	forces (2213.6 Item 2).

	If they are judged to be PR, then they must be TESTED to
	determine the inelastic rotation capacity (2213.6 Item 3.2),
	in addition to other design criteria.

	Any comments would be appreciated, including whether CP groove
	welds are possible on A570 10 gage material.

	Mark Swingle, SE
	Oakland, CA

	These are my own opinions....