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RE: Joist Girder Moment Frames

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Given the large difference in moment, I would assume that your 115 K' moment
includes the dead load.  The connection does not become moment resisting
until you make the bottom chord weld.  It is common to specify that all
welds to the bottom chord be completed after all dead loads are in place.
Therefore, your connection only has to resist the live load and wind load
moments.  You will of course have to also add the moment resistance required
to insure stability of the columns.

Vulcraft also publishes a book entitled, "Designing with Steel Joist, Joist
Girders, and Steel Deck."  This book includes a number of different
connections that may be applicable as well as the limiting loads typical for
each type of connection.  I highly recommend obtaining a copy.

Additional items to watch for:  the detail of the joist to column connection
at the joist girder/column connection.  If your plate is continuous across
the top of the column, the joist seat will have to be modified to take into
account the thickness of the plate; or you may have to have a seat
connection for the joist.

Brian K. Smith, P.E.
Louisiana

> -----Original Message-----
> From: Michael Zaitz [mailto:mzaitz(--nospam--at)hgbd.com]
> Sent: Monday, August 28, 2000 9:40 AM
> To: seaint(--nospam--at)seaint.org
> Subject: Joist Girder Moment Frames
>
>
> 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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