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

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Mark,

I'll take a stab at it.  See below for my responses.

I hope this helps.

Regards,
Harold Sprague

> -----Original Message-----
> From:	Swingle, Mark [SMTP:Mark.Swingle(--nospam--at)dgs.ca.gov]
> Sent:	Monday, January 24, 2000 11:33 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?
> 
> 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.
> 
> -------------------------------------------------
	[Sprague, Harold O.]  From the description, I assume that the
channel beams are welded to opposing faces of the tube steel column.
Generally, if the flanges do not have some mechanical method of continuity
("...no stiffener plates or continuity plates..."), I assume that these are
PR. They transmit compression and tension forces to the tube steel wall
which must resist them in flexure / bending.  How much flexural rotation
occurs in the connection is anybody's guess without testing or FEA analysis.

	Testing may indicate that they are closer to FR.  You may have a
very thick TS wall and light channels framing into them.  Or it could be
more of a PR with very big MC channels and a 3/16" walled TS column, but it
is impossible to determine from what we are given so far.


> 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.
	[Sprague, Harold O.]  You can get a CP weld, but a CP groove weld is
a little more difficult.  I would avoid CP welds and use a fillet if
possible.  There is a tendency to keep the amperage up too high and burn up
the gauge metal, but good welders can do them.  

	Look at the prequalified welds in the AISC manual.  You will see
that with gauge metal you would be forced to a weld with a root opening of 0
and an f of 0.  This limits your choices of CP groove welds.


> Mark Swingle, SE
> Oakland, CA
> 
> These are my own opinions....
>