Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Steel: Moments in joist seats.

[Subject Prev][Subject Next][Thread Prev][Thread Next]
In the case of a joist-girder resting on top of a tube column, there is a
common detail which extends the top plate of the column a couple of inches
along the seat of the joist.  The joist then has a top chord extension (TCX)
to match the coverplate length.

The question was raised by the EOR, of whether the offset of the centerline of
the column and the bearing point of the column by 5 inches would cause a
moment in the column and in the top chord of the joist-girder.  I can see how
this might occur, but this is the only time it has been questioned.  The SJI
specifications don't address the possibility of a moment being induced by
deflection of the bearing plate.

(The SJI specifications call for a design based on simple span and that is 98%
of the time what the engineer is happy with.  The other 2% of the time, the
engineer normally specifies what moment will be applied to the top and bottom
chords and what details are required for attachment.)

My intuition (never to be totally trusted) tells me that the top chord would
plastic hinge at the attachment to the much stiffer seat creating the
idealized pin condition anyway.  This may cause problems of its own.

Has anyone else run across this detail and thought about the potential moment?

Thanks for your time.

Valerie Eskelsen