B31.1 S_A w/ "Footnote 2" Materials

[StevenHPerry]

This probably falls into "who cares?" but I'm still curious.

Reference B31.1 equations 1A (S_A), 1B (S_A liberal), 11a (S_L), and footnote 2:

"For materials with a minimum tensile strength over 70ksi, eqs (1A) and (1B) shall be calculated using S_c or S_h values no greater than 20ksi, unless otherwise justified."

With a material that qualifies for that footnote, S_c = 25ksi, S_h = 25ksi. I could push S_L to 25ksi. Equation (1A) (f=1.0) would give 30ksi considering the 20ksi max for S_c and S_h, but the liberal allowable would be:
1.0*(1.25*S_c + 0.25*S_h + (1.0*S_h - 1.0*S_L)) = 25ksi.

Eq 1A = 30ksi
Eq 1B = 25ksi

This seems counter-intuitive to me. Is that how you read the code as well?

Should the sustained load margin be taken with S_h = 25ksi still? Would that fall under "further justification"? 1B simplifies things down to one S_h term, so maybe that is not stretching.

- Steve Perry

http://www.linkedin.com/in/stevenhperry

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