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

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Levi and Salvadori's "Why Buildings Fall Down" is a great lay persons
reference book on structural failures, and it describes many types of
failure.  One chapter is devoted to the effects of unstable soils. 
Another deals with engineering and the law.  The appendix contains a
very good description of structural systems.  This chapter mentions a
case in which some houses built on top of a hill of clayish soil came
home to find their homes at the bottom of the slope.

An excerpt on Equilibrium: "A structure not only must be stable - that
is, not be subjected to large displacements - .... it must be in
equilibrium (in balance).  This requirement implies, of course, that
each element of a whole structure must also be in equilibrium so that
the structure will stay together."

I highly recommended book to anyone interested in structural failure
or stability for any reason.  The companion book "Why Buildings Stand
Up" is also excellent.  Many engineers I know have both in their

Kieran K-S

----- Original Message -----
From: Syed Faiz <sfaiz(--nospam--at)>
Date: Tue, 27 Jul 2004 19:53:29 +0300
Subject: RE:Definition of Unstable ===>>what SALVADORI has to say
To: seaint(--nospam--at)


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

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
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
Saudi Arabia
Cell: +966-508-169304

-----Original Message-----
From: Caldwell, Stan [mailto:scaldwell(--nospam--at)]
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.


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

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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