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Structural Steel Properties

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Gerard Madden wrote:

>>> On a side note, I was taught in Grad school that I should always
consider A36 to have an Fy=50 ksi, since mills today produce mostly dual
spec steel.  This recommendation was brought up in an EBF lecture.  Does
anyone think it is appropriate to always use A36 w/ Fy=50 ksi in all NEW
construction for any application (even angles and channels)? <<<


Philip T. Hodge responded:

>> NO!  A36 often has 50 ksi yield, but not always.  45 to 49 ksi is not
rare.  Sometimes what is sold as A36 is what couldn't make it as A992 or any
of the Grade 50 modifications to other steels. <<


And, Charlie Carter responded:

> If you specify A36, it is my opinion that you should calculate the
strength of a member based upon Fy = 36 ksi, because that is all the
producer is obligated to provide per ASTM A36.  It is likely that the actual
yield strength is higher than that however.  Wide-flange shapes
should be specified as A992 (Fy = 50), and doing so will let you design with
Fy = 50 ksi.  M, S, and HP-shapes and channels are commonly
specified as A36, A529 Grade 50, and A572 Grade 50 with industry trending
towards the two 50 ksi specs (but not 100 percent there yet... check with
your local fabricator).  Angles and plates are usually A36, although there
may soon be a trend toward moving these along to a 50 ksi base steel too.

Now for high-seismic design, where you are not calculating the strength of a
member, but rather the demand that will be induced on a connection, column
or other member due to inelastic deformation of another element in the
structure, your assumption of Fy should be different. For example, in a
moment frame, you expect to hinge the beam, so the connection to the column
and the column have to be good enough to do it.  That means you have to use
a more realistic estimate of Fy.  In the AISC Seismic Provisions, we use an
Ry factor.  For A36 W-shapes, Ry = 1.5.  For A572 Grade 50 W-shapes, Ry =
1.1.  The end result is that the expected Fy is essentially the same.

Hope this helps.


Charlie <



My comments are in two parts -- sincere and not so sincere (maybe downright
rude).  First, the sincere part.  I agree completely with Philip Hodge's
response (above), and almost completely with Charlie Carter's response.  To
Charlie's response, I would have added that control of the upperbound
material properties is automatically provided under the new ASTM A 992, but
when specifying material according to the older standards, like ASTM A 572,
one should also require compliance with the additional requirements of AISC
Technical Bulletin Number 3, New Shape Material, dated March 3, 1997.

Now for the not so sincere part.  If LRFD really rules, is it good enough to
make up for using the wrong material properties in design or for
incompletely specifying the material properties?  I don't think so!


James H. Stamper, PE (Jim)
Senior Structural Engineer
Heery International, Inc.
Atlanta, Georgia
(E-Mail:  jstamper(--nospam--at)heery.com)


P.S.  I think that we should require the next guy who shouts "LRFD Rules" to
admit how many body piercings he/she has!!!  After two years of reading
these rantings, I can't take it anymore.  You LRFD fanatics wanted to
provoke comment?  Fine, just get ready to be smacked with a strong dose of
reality (you won't like what you hear, but it'll be more truth than you've
been fed so far).  You can expect a lot more on this when I've got time
(sometime during the coming week).