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FW: Copy of: Underpinning Ex

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You have gotten a lot of good, and sometime controversial advice.  Let me add a little more to the above discussed subject.

Be cautious about using Hlicoil or similar type devices.  They may significantly change the way you grade beam footing works.  You are introducing a rigid support underneath your grade beam, and consequently a moment at the top face of it.  Now you foundation is a multispan beam instead of the beam on elastic foundation.

In my experience older buildings, if they have any reinforcement at all, might just have rebars at the bottom only.  So by introducing rigid supports you are adding to the foundation distress, rather that helping it.  Of course there are considerations of settlements that you should be concerned with, but this is a different topic.

What I've done in the past, that was found sometime a cheaper option, was adding a continuous grade beam on the exterior side of the existing footing either at the places of visible distress or, if budget permits, along all bearing walls.  Existing trapezoidal foundations are always eccentric, so by adding the new grade beam on the outside you are eliminating eccentricity ( which may cause the rotation of existing footing in case of additional loading), and add to the bearing area.

My one rouble worth.


Sasha Itsekson, P.E.

From: 	Kathleen  A. O'Brien[:wildwoman1(--nospam--at)]
Sent: 	Wednesday, November 26, 1997 12:10 PM
To: 	INTERNET:seaoc(--nospam--at)
Subject: 	Re: Copy of: Underpinning Ex

Thanks! I will start tracking down Helicoil.

Kate O'Brien