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RE: Concrete Pedestal W/ Column Thrust & Tie-Rod

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I see what you're saying, and you could throw the hooks in at the top;
behavior would have to be dominated by shear though (i.e., keep the ties
close; typical of deep beams).  If you have a exterior concrete wall
(spanning between piers) you could treat it as a "T" section to help.

Robert Rogers, PE

-----Original Message-----
From: Ed Fasula [mailto:tibbits2(--nospam--at)metro.lakes.com]
Sent: Wednesday, September 20, 2000 3:26 PM
To: seaint(--nospam--at)seaint.org
Subject: Concrete Pedestal W/ Column Thrust & Tie-Rod


We have a situation where a pre-eng. steel building column with 46k outward
thrust needs a pedestal with the tie-rods placed 2' below the steel base
plate (which has a shear lug).  It's a riding hall with no floor.

The footing and pier has been designed for the couple moment, to the point
where I was considering the need to hook the pier verts at the top (below
the base plate) to develop the bars.  I have not seen this done before, and
intuitively, I though that the force between the base plate and the tie rod
would be transferred essentially by concrete shear and the horizontal ties.

After looking into MacGregor's chapter on deep beams, and looking at the 2'
tie rod offset as a span, the pier, 2'-8" deep, is even deeper than the
span.  An extreme case of a deep beam in that light.  MacGregor explains
that the force in the pier tension rods would be virtually constant, and
states that "...this force must be anchored at the joints."  He goes on to
describe design following the Plastic Truss Theory.

Am I on the right track here?  By this reasoning, hooks at the top of the
pier are critical.

Regards,

Ed Fasula, EIT


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