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Re: Increasing Kl/r

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Paul,

FWIW, I think your solution is both technically valid and clever, but with
one proviso.  You say that the a new, "... r value would be calculated for
the combined section with both the existing and new parts contributing."
You should be careful about how you calculate that radius of gyration.  It
is not obvious that the inner section won't have to experience local
yielding (go into a "pre-buckling" mode) before the new shell can act to
prevent a failure.  Your "buckling resisters" may act more in series rather
than in parallel.

It is probably conservative, but you might consider accounting for this
effect by ignoring any buckling resistance in the inner pipe -- relying
solely on the moment of inertia of the new outer pipe (the "buckling
preventer") in your calculation of the effective radius of gyration.  This
will likely force you to use a slightly bigger, "shell," but you'll sleep
better too.

Drew Norman

----- Original Message -----
From: Paul Feather
To: SEAOC List
Sent: Monday, May 07, 2001 6:18 PM
Subject: Increasing Kl/r

... existing trusses (wide flange chords, pipe webs) with a 130 foot span
... everything ... OK except one diagonal ... sufficient area ... if the
Kl/r could be reduced ...


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