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RE: Definition of Unstable

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In 1997 I reviewed a precast concrete structure that had "some cracking". It had been reviewed by several other structural engineers. I wrote a memo stating that the structure was not safe for human occupancy. I am not an alarmist, but the other structural engineers that had been on site had no exposure to precast concrete buildings. They had not arrived at the Socratic plane. They were competent engineers, but just did not understand what was happening to this particular type of structure.

I would suggest that you scour Timoshenko and Gere's, Theory of Elastic Stability. There are many references and examples of stability that might help your cause. No engineer will argue with Timoshenko.

Harold Sprague

From: "Caldwell, Stan" <scaldwell(--nospam--at)>
Reply-To: <seaint(--nospam--at)>
To: "SEAINT Listserv" <seaint(--nospam--at)>
Subject: Definition of Unstable
Date: Mon, 26 Jul 2004 14:57:44 -0500

Once again, I find myself employed as an expert witness in the defense
of a fellow structural engineer.


A concrete tiltwall industrial building was constructed in 1976 and
expanded in 1991.  Due primarily to differential heaving of expansive
clay soils, the building suffered substantial distress over a period of
many years.  By 1999, the distress had progressed to a point where the
building owner brought in three separate structural engineers to observe
the condition of the building.  All three engineers independently
concluded that they observed significant structural problems and
recommended further testing, repair and monitoring programs.  The owner
apparently ignored these recommendations, and instead proceeded to sell
the building to the tenant in 2000.  Less than a year later, the roof
collapsed.  An insurance company subsequently paid a claim well in
excess of $2 million, and is now subrogating against (suing) all three
engineers.  The allegations principally are that the engineers:  (1)
failed to include warnings about the immediate need for repairs, (2)
failed to include warnings about life-safety issues, and (3) failed to
report that collapse was imminent.

Key Question:

The engineer that I am defending wrote a two-page report summarizing the
observed damage and recommending specific repairs, tests, and
monitoring.  Prior to a list of nine items, one key sentence reads:
"Please find listed below items that need to be completed immediately
and prior to any other investigations."  In my opinion, this sentence
directly refutes the first allegation.  Another key sentence reads:  "It
is my opinion that the building is relatively unstable at this time with
differential floor slab and wall panels movements noted."  In my
opinion, this sentence indirectly refutes the third allegation because I
consider an unstable building to be a building where the risk of
potential collapse is imminent.  What I need to support this opinion is
a good written definition of "unstable".  Preferably, I would like to be
able to refer to a well-written paragraph in a widely recognized text or
other reference.  Any suggestions?


Stan R. Caldwell, P.E.
Dallas, Texas

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