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Basic nomenclature question

Basic nomenclature question

Basic nomenclature question

(OP)
What does or where did the subscript "a" come from for required strength in ASD design? As in Ma, Ra, Pa, etc.

Shouldn't it be called "r" instead or something so people don't confused it with "allowable"?

RE: Basic nomenclature question

Ever since I was in school back in 1976, I have used the "a" subscript to indicate "allowable".
Dave

Thaidavid

RE: Basic nomenclature question

Yup. Allowable.

RE: Basic nomenclature question

Take a look at the start of section 2 of the AISC manual, this describes the nomenclature quite well.

Subscript n (Rn) is the nominal capacity. Essentially the capacity with no adjustment for LRFD or ASD.

Subscript a (Ra) is the required allowable capacity for ASD. Ra ≤ Rn/Ω.

Subscript u (Ru) is the required ultimate capacity for LRFD. Ru ≤ φRn.

I can see your point, though. You would think subscript r would be used for "required". This is done somewhat, if you look at chapter H for combined forces in AISC 360 you see that Rr is the "required" strength for LRFD or ASD.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries
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