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Re: Steel: Moments in joist seats.

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My common design practice is to design columns for the moment induced by
the eccentricity of the joist girder bearing and single span loading.
For long spans or cantilever to hinge conditions I also check the moment
induced in the column by the expected rotation of the beam. Most details
for joist girder support include welds from the top chord bearing seat
to the column cap plate and / or welded knife plate drag connections
creating far less than an idealized pin condition. 

Though some local deformation, or hinging, of the girder top chords is
probable, the effective top chord section is stiffened by the nailer and
sheathing or roof deck attachments transfering the burden back to the
often times too slender column element.

The increased column size is not dramatic, and the resulting design is
compatible with the P-delta requirements for seismic displacement.


Paul Feather PE