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Re: MISC - Mill Certification/Higher Yield Stress

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Our office standard for ductile frame design was to use A36 material for the
beams and A572 50ksi for the columns, mostly to ensure strong column weak beam
behavior. The design was based on plastic section properties and load factors
(AISC Chapter "N"), and our notes specified a maximum yield of 42 ksi for the
A36 material. I recently (1995) designed a project with ductile steel moment
space frames where the fabricator contacted me to say that it was IMPOSSIBLE
to obtain such material, that 51 ~ 53 ksi was as close as could be
gotten.......and it would be a range. My response was I thought it could be
found and had been before, so quit crying and get it. He then got an AISC
person to call me back to tell me that 42ksi material was not being produced
in the United States anymore (due to the high quality of the scrap). So I was
forced to revise my design for the frames to use 50ksi as the yield for the
beams also, and this necessitated increasing the column sizes considerably(the
beam mill certs came back at 54 ksi). But the SAC committee on ductile frame
design recommends using values much higher than 36 or 42 ksi for the actual
yield, since the steel being produced averages 50 to 55 ksi yield, even though
it may be graded ASTM A36. Incidentally, our office did a project approx 9
months before my project, and we got mill certified 42 ksi yield beams,
exactly as specified......from Japan. Anyway, to be on the safe side, I now
use 50ksi as design yield stress for everything, plastic design or ASD.....and
specify A572 Gr 50 exclusively.

                  Monte Griffiths, RCE