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Re: EBF's

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The strength of steel and the very ASTM designation is in a state of
flux.  The mills and ASTM are attempting to address the weldability,
ductility, and dual certification issues at the same time.  Most all
structural shapes produced today are dual certified.  Currently on the
A572 side you can require "special requirements".  The special
requirements will:
1.  Limit carbon equivalent to 0.50 max.
2.  Limit Fy to 65 ksi max.
3.  Limit yield to strength ratio to 0.85 max.
4.  Give a max tensile strength of 65 ksi.

Generally the ASTM refers to any additional requirements as
"supplementary requirements".  Regardless, I called a few mills to see
what the impact was on availability and cost.  I was told that it was
just a paper problem, and that most of the current steel produced
generally meets the "special requirements".  Further, there was no extra
cost over regular A36 steel.

As with anything that is in a state of flux, you will probably want to
verify this on your own.  Call the mills that produce the majority of
the shapes you are considering for your link beams.  Get their input,
but my sources in the AISC indicate that the "special requirements" will
soon be the standard.

The design of reinforced concrete special moment resisting frames
addressed the overstrength issue years ago by requiring an upper limit
on rebar strength and by calculating an amplified plastic moment.

I agree with the concerns.  In theory you could have some steels maxed
out on various alloying compounds that could give much more strength in
the link beam section.  The use of recycled steel and the newer electric
arc furnaces have the ability to create higher strengths than in the
past.  The same over strength problem could happen on special moment
resisting frames.  The design formulas for steel EBF's and SMRF's
attempt to take this overstrength issue into account, but the
overstrength provisions are not as obvious and encompassing as they are
in reinforced concrete.

Bottom line.  If you are concerned about the upper strength of steel,
specify a maximum strength consistent with what the mills can produce
and put in your specs.  It should not impact cost, availability, or
schedule.

Regards,
Harold Sprague
Black & Veatch


 ----------
From: Paul McEntee
To: seaoc(--nospam--at)seaoc.org
Subject: Re: EBF's
Date: Sunday, September 07, 1997 9:31PM

> If the nominal strength is 36 ksi for link beam and for bracing,
> increasing 50% the force in bracing is similar to thinking that the link
> beams have equivalent strength of 36ksi x 1.5=54 ksi.  It is not
> inconceivable that the steel supplied for the link beam could be dual
> cert or A36 having actual strength higher than 54 ksi, since ASTM do not
> have upper limit for Fy.  Should this be the case then the link beam may
> not yield first as designed.
>
> Y. Henry Huang
>