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Re: Definition of Unstable

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From Engineering Mechanics, R.D. Snyder and E.F. Byars, McGraw Hill, 1973, p. 393 (my college text in the Introduction to Mechanics course at Cornell U. back in 1974)
"Essentially, a stable equilibrium situation is one for which a slight change in loading or geometry produces a correspondingly small change in the support reactions and/or configuration of the body or structure; i.e., a small disturbance results in a  small response."
From the Penguin Dictionary of Civil Engineering, John S. Scott, Third Edition, 1985, Penguin Books Ltd.,
"The resistance of a structure to sliding, overturning, or collapsing. A structure can be tested (on paper) for stability by verifying that it tends to return to its original state after being disturbed."
Means Illustrated Construction Dictionary, New Unabridged Edition, R. S. Means Company, 1991,
Definition of stability: "A measure of the ability of a structure to withstand overturning, sliding, buckling, or collapsing." 
Unstable is the opposite of stable. Hope this helps.
James Cohen, PE
James Cohen Consulting, PC
----- Original Message -----
Sent: Monday, July 26, 2004 03:57 PM
Subject: Definition of Unstable

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