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RE: Column Base Pocket in Slab

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The most common detail for metal building manufacturers is to have no pocket
for columns.  Typical metal buildings are designed as a 3 hinged arch, and
develop a significant lateral thrust at the base.  The anchor bolts are also
commonly placed between the flanges in the base plate (in part to avoid a
tripping hazard).  The lateral thrust is resisted in the anchor bolts, the
anchor bolts are commonly confined by a rebar hairpin around the anchor
bolts and lapping onto the reinforcing steel in the slab on grade.  The
reinforced slab on grade acts as a tension tie for the arch.

In conventional commercial and light industrial steel buildings it is common
to provide pockets and recess the base plate and anchor bolts.  In heavy
industrial buildings, it is more common to not recess the base plate.

All that said, it is important to not tie the column to the concrete slab on
grade.  The tie provides a restraint for slab shrinkage, and a restraint
will result in cracks in the slab on grade.

With all that, there are exceptions to every rule.

Harold Sprague

> -----Original Message-----
> From:	rlewis(--nospam--at) [SMTP:rlewis(--nospam--at)]
> Sent:	Tuesday, April 18, 2000 3:19 PM
> To:	seaint(--nospam--at)
> Subject:	Column Base Pocket in Slab
> I am working on a building that has some steel columns.  The building is a
> light wood framed structure.  The foundation is a turned down slab on
> grade. 
> I have a few steel columns in the building.  A little divergence here to
> make
> a point.  The last time I designed a metal building the contractor asked
> me
> why I did not recess the column base plates into the slab to cover the
> anchor
> bolts.  I told him I understood metal building people preferred to bear
> the
> column on top of the slab.  He told me he commonly recessed the column
> bases
> into the slab.  With this building the foundation is similar to a metal
> building, a turned down slab.  I would like to recess the column bases
> into
> the slab to hide the anchor bolts and help with detailing the rest of the
> structure.  Is it common to put in a "column pocket", say down 8 inches,
> as
> you pour the slab so that the base of the column can be recessed into the
> slab?
> Thanks for your help.
> Rich
> __________________________________________________
> Richard Lewis, P.E.
> Missionary TECH Team
> rlewis(--nospam--at)