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

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Mark,
IMO, I do not believe there is an easy answer to your question.  I am
remembering my advanced steel design class where we analyzed connections ...
the process involved finding the end moments and rotations.  If these values
were greater than "x" then the connection was considered fixed.  If the
values were less than "y", it was considered pinned.  Anything in between
was considered a partially restrained connection.  
You can model a fixed beam to column connection in a computer analysis
program; however, the structure will behave relative to each member's
stiffness.  For example, if the stiffness of the beam is 1000 times greater
than the stiffness of the column, the structure will behave as if there is a
pin connection at the end of the beam regardless of the fixed condition
input.  The "toothpick" column can only resist its share of moment and the
rest must be resolved in the beam.
Check out the following:
Section 5 of Design of Welded Structures by Blodgett and 
A Simplified Look at Partially Restrained Beams by Geschwindner (Second
Quarter/1991 AISC Engineering Journal)

Hope this helps ...
William J. Keil, P.E.



-----Original Message-----
From: Swingle, Mark [mailto:Mark.Swingle(--nospam--at)dgs.ca.gov]
Sent: Monday, January 24, 2000 12:33 PM
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....