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Re: Definition of Unstable

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Jim Wilson wrote:
Definition of instability:
"A structure or one of its elements is on the verge of instability when a small increase of load, or a small disturbance, will result in a large displacement."
in theory of structure, it is call "geometric instability". (see Kinney p27)
 
Here is a definition of STABILITY, from "Indeterminate Structural Analysis" by J.S. Kinney, Sddison-Wesley Publishing Company, 1957, page 21:
A stable structure will support any conceivable system of aplied loads, resisting these loads elastically and immediately upon their application, the strength of all members and the capacity of all supports being considered infinite
 
"..., the strength of all members and the capacity of all supports being considered infinite." it is an assumption for structural analysis only.
 
Hope this will help.
 
Best Regards,
 
Junata
Surabaya, Indonesia
 
 
----- Original Message -----
From: Jim Wilson
Sent: Tuesday, July 27, 2004 10:32 AM
Subject: Re: Definition of Unstable

Definition of instability:
"A structure or one of its elements is on the verge of instability when a small increase of load, or a small disturbance, will result in a large displacement."
-Yura/Galambos/Helwig/Green, quoted from Basic Design for Stability course notes, Part I Lecture 1, as presented at the AISC convention in 2003.
Far from a widely recognized text, but certainly by widely recognized individuals.
 
Jim Wilson, PE
Stroudsburg, PA

"Caldwell, Stan" <scaldwell(--nospam--at)halff.com> wrote:
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 t! hat 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&nb! sp;refer to a well-written paragraph in a widely recognized text or other reference.  Any suggestions?  
 
Regards,
 
Stan R. Caldwell, P.E.
Dallas, Texas


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