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RE: Pinned Base Plate or Fixed

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Another interesting aspect of this is the practice in the metal building 
industry.  The metal building industry commonly assumes a 3 hinged arch in 
which the beam to column connection is rigid, but the column to foundation 
is considered a pin.  The pinned base is a rather thin base plate with 4 
bolts.  The concept is to make the column to foundation connection rigid 
enough to accommodate out of plane loads induced during construction, but 
will not induce a significant moment in the plane of the arch.  The joint 
at the ridge is assumed to be a pin.

The AISC has a Design Guide 1 which has some examples of base plate designs 
 that transfer shear and are assumed pinned.  Figure A1.2 illustrates a 
base plate that (if the anchor bolts are tensioned) would be a moment 
connection.  By using the "stool" concept, the flexibility of the base 
plate will not contribute to the rotation and by tensioning the bolts, the 
bolts will not contribute to the rotation.

The stresses are one aspect in the base plate to foundation connection. 
Another is how much the flexure contributes to the rotation of the column. 
It is that rotation that will determine if the base plate is "assumed pin", 
 partially flexible, or fixed.  That should be the focus of any FEA model 
of the column base to foundation connection.

Regards, Harold Sprague

> From: behnamheydari_80(--nospam--at)
> Date: Sun, 22 Sep 2013 16:23:25 +0430
> Subject: RE: [SEAINT-SEAOSC] Pinned Base Plate or Fixed
> To: seaint-seaosc(--nospam--at)
> Harold,
> Thanks for your help,
> As far as AISC implies "A ductile moment frame is usually expected
> to develop a hinge at the base of the column", we need to accommodate
> details in which plastic hinge will be formed whether at column (Fixed
> Base) or base plate (Pinned Base).
> So as you mentioned a sophisticated FE model of connection should be
> developed to ensure that all connection components have enough strength 
> to restrain the connection (Fixed Base) or base plate and anchor rods can 
> be maintained up to the maximum rotation that may occur in Pinned Base 
> (in this case we have partial fixity not zero moment).

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