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RE: Steel Beam Reinforcing

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npitera(--nospam--at)mmm.com wrote:

> Are you saying that if you have a steel beam that is stressed way
> above 36 ksi (assume Fy=36 ksi) and you add a steel plate or
> whatever, and no stress relief is provided, and say no future loads
> are applied, the steel beam will somehow know to share the existing
> load?
> Interesting.......................
> But I don't buy it, and I wouldn't stake my P.E. on it.

Response:

No, that's not what anyone has been saying.

If material is added to a section (and the original material and the
new material are ductile), the ULTIMATE force or moment capacity of
the resulting composite section is not significantly affected by the
initial state of stress.

Regarding your example, if your calculations indicate that "a steel
beam ... is stressed way above" yield, then your linear, elastic
calculations are wrong because the material is yielding.  If your
section has performed acceptably (safe and serviceable) and "no future
loads are [to be] applied", why would you add material?  If you do add
material and continue to increase the load, the section  DOES know how
to share the load--it yields.

If, when you beef-up a section, you are concerned about the future
displacement response and you want to prevent yielding of the
material, you should take the initial state of stress into account and
linear, elastic calculations are probably okay; unloading the member
before adding material is likely a good idea. (If you really are
terribly concerned about the "actual" displacements and you really
want to prevent ANY yielding of the section, residual stresses should
be considered--not an easy thing.)

If, however, you are concerned about the actual CAPACITY of the
section (and buckling is not a concern, etc.), the initial state of
stress is not very significant and plastic calculations best reflect
what ultimately happens to the section.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Michael Valley, P.E., S.E.                   E-mail: mtv(--nospam--at)skilling.com
Skilling Ward Magnusson Barkshire Inc.              Tel:(206)292-1200
1301 Fifth Ave, #3200,  Seattle  WA 98101-2699      Fax:        -1201


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