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Re: Steel Modulus and Strength

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I doubt there are many structural engineers out there who haven't struggled
with the fact that engineering is not science.

The simple fact is that often times we are working with materials whose
properties cannot be accurately defined.  Concrete is normally specified to
be a minimum compressive strength; specify 3,000 psi and you might end up
with 4,500 psi (and that's just at 28 days).  Reinforcing and structural
steels are similarly specified.  These are quasi-manmade products, where
quality control results in better guesses.  How does one accurately predict
performance of a piece of wood without knowing all the knot locations,
growth history, moisture content, etcetera?

As for me, I'm not sensitive to the assertion that structural engineering is
backward relative to other disciplines.  My daughter is a third year medical
student at the University of Iowa; I think she'd be quick to say an MD does
not practice science.  She might even say that MD's "treat for diseases and
maladies we don't know.....utilizing salves, ointments, oils, and drugs
whose behavior we don't understand....etc...etc...etc...."  Of course,
medicine has a basis in science, just like engineering.  MD's and structural
engineers must "bracket" their solutions . . . just like the rocket
scientists at NASA, where they do work that is close enough for the
government.

John P. Riley, SE
Riley Engineering
Blue Grass, Iowa


----------------------------------
 I know that. It doesn't make any difference as to the amount of
reinforcement one utilizes....

It does however make a difference when one is attempting to step out of the
cook-book code driven pseudo-design mentality, and truly wants to engineer a
structure...

I believe responses like that perpetuate the backwardness of
civil/structural engineering in relation to other disciplines.

It's like saying...we don't really know ...but it's close enough for
government work.....

It perpetuates the definition of structural engineering ... which
interestingly enough was removed from the SEAOC web site home page...that we
"design for forces we don't know.....utilizing materials whose behavior we
don't understand....etc...etc...etc...."

If anyone out there has a less condescending or simplistic answer, and truly
knows which value is closer to the actual value...please let me know...

jim

> >It doesn't make any difference.
> >
> > It doesn't make any difference.
> >
> > It doesn't make any difference.
> >
> > A. Roger Turk, P.E.(Structural)
> > Tucson, Arizona
> >
> > Jim Korff wrote:
> >
> > >>Is the correct E Modulus for steel rebar 30,000 ksi  or 29,000 ksi ??
> >
> > Is the correct yield strength of  Grade 60 rebar 60 ksi or 58 ksi ??
> >
> > Is the correct yield strength of  Grade 40 rebar 40 ksi or 38.7 ksi ??<<
> >
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