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RE: Steel Beam Reinforcing

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Highly variable residual stresses from section forming, fabrication,
and erection make traditional linear, elastic section analysis "a
grossly inaccurate simplification".  A plastic analysis is also
"grossly inaccurate" but has the appeal that it is correct at at least
one point in the response history of a ductile member loaded to
failure.  Whether this reality is popular or not, the ultimate
capacity of a ductile, composite section is not very sensitive to the
loading history.  Decades of testing has proven this time and time
again.

I believe this fact is behind Harold's observation (please correct me
if I've misrepresented you Harold).  In the referenced paper Tide
reports, "O'Sullivan tested trusses that had been reinforced (bolted)
with and without applied load and determined that there was no
substantial difference in the ultimate strength between the two
procedures.  However, when the trusses were reinforced under load, he
determined that there was a 50 percent increase in deflection before
full cross-sectional yielding occurred."

Where the design objective is to avoid loading a structure beyond its
ultimate capacity, the subtleties of loading history may not be
significant.  Where the design objective is to meet certain
(non-life-safety) serviceability limits, such load history may be
important.

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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

-----Original Message-----
From: npitera(--nospam--at)mmm.com [mailto:npitera(--nospam--at)mmm.com]
Sent: Wednesday, July 19, 2000 1:22 PM
To: seaint(--nospam--at)seaint.org
Subject: RE: Steel Beam Reinforcing


"Initial stress in the parent member not important?" You must be
kidding!
You must prorate your loads ( if you do not relieve the member somehow
by
jacking or some other method).
To say that can just throw all the load, present and future into the
newly
composite member is a grossly inaccurate
simplification of structural analysis.


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