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Re: UBC97-- Redundancy Factor

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At 10:42 PM 2/26/99 -0500, you wrote:
>
>Has either of the individuals that responded to my message read the
>article?       [In a recent edition of the ASCE jourlan of Structural
>Engineering there was an interesting article by Bertero & Bertero on the
>advantages of redundancy.]
>
>
>Mark Gilligan
>
        No, but your summary of it made sense immediately on its face. I
responded with approval, using an example from early day aeronautics, with
the conditions carefully qualified to be analogous. 

If the remaining frames are incapable of the job if any frame fails, then
multiple frames, like multiple engines in my example, are a disadvantage.

If the remaining frames can still do the job, like the remaining engines on
a returning bomber or airliner in Christopher Wright's example, then the
redundancy helps, assuming the probability of any one frame failing hasn't
become too much worse.

Your summary left the impression that if the members are loaded well into
inelastic conditions, then total inelasticity could result if one member
failed. That is, you can't still fly on the survivors.

As for interpreting the article, I know you, and if you misunderstood the
article then the article was not well written. I should expect to do no
better with it.

The caveat is: If we do have redundancy, are we getting cavalier or slipshod
as to the reliability of any one element, or as to the survivors being truly
sufficient if one fails?   Like with flying, one must be aware of what one
is relying on, and its limitations, because mistakes make wreckage.

Charles O. Greenlaw  SE    Sacramento  CA