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Joist Girder Moment Frames

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Hello

Regarding Moment Frames made with Joist Girders and Columns.  I have a warehouse
that I am using the joist girders to create moment frames for lateral stability
(wind controls).  Vulcraft has some details to follow to create this connection.
One of the details is the use of a plate for the bottom chord of the joist girder
to weld to the column and a plate that is laid on the top of the joist girder and
the column cap plate and welded to both.  My question is can the weld to the
column cap plate be sized only for the moment that the column will be resisting?

The numbers I have are 115 k*ft of moment (both counter clockwise) each side of
the column for a force of ~35 kips at the top chord for each girder.  However with
the frame action the column is only resisting 35 k*ft.  With 40 inch deep joist
girders the force due to the moment couple is 35*12/40 = 10.5 kips.  A significant
reduction in weld.

The plate would have to be designed as a short column.

This was brought up in discussion and it does not seem right but for some reason
the answer eludes me.  What am I missing here?

Mike Zaitz




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