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RE:Definition of Unstable ===>>what SALVADORI has to say about STABILITY.

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Stan:
 
I know you already have been swamped by a host lot of stuffs vis-a-vis the definition of "unstable", "stable" , instability or "stability' and I think you probably do not need any more of the same.
 
However, I was browsing through a classical book that I have with me, entitled, "Structure in Architecture" by: Mario Salvadori et al. I found something interesting related to your query per se  in the same and thought may be I should share the same with you and others on this list.
 
This is what Salvadori has to say about stability and I QUOTE:
 
"The requirement of 'Rigid Body' stability is concerned with the danger of unacceptable motions of the building as a whole. When a tall building is acted upon by a hurricane wind and is not properly rooted in the ground or balanced by its own weight, it may be topple over without disintegrating. The building is said to be UNSTABLE in ROTATION. This is particularly true of tall narrow buildings, as one may prove by blowing on a slim cardboard box, on a rough surface.
 
The danger of ROTATIONAL INSTABILITY is also present when a building is not 'well balanced' or is supported on a soil of uneven resistance <may be this one is more appropriate to your case, being founded on expansive soil>. If the soil under the building settles uevenly, the building may ROTATE, as the Leaning Tower of Pisa still does, and may eventually topple over. <UNQUOTE>.
 
I hope this is of some value to you or to any on this list. Best regards to all.
 
Syed Faiz Ahmad; MEngg, MASCE
Senior Structural Engineer
Saudi Oger Ltd
P.O. Box: 1449
Riyadh-11431
Saudi Arabia
Cell: +966-508-169304
-----Original Message-----
From: Caldwell, Stan [mailto:scaldwell(--nospam--at)halff.com]
Sent: Monday, July 26, 2004 10:58 PM
To: SEAINT Listserv
Subject: [SPAM] - Definition of Unstable - Bayesian Filter detected spam

Once again, I find myself employed as an expert witness in the defense of a fellow structural engineer. 
 
Background:
 
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?  
 
Regards,
 
Stan R. Caldwell, P.E.
Dallas, Texas