huangyhg

chapter 6: aisc 13th edition
i just now noticed this chapter and the tables for combined loading.
does anyone actually use it? how can it be a simplification/"design aid" of ch. h?
i thought spec. ch. h was about as simple as it gets. am i just totally missing the benefit of ch 6?
i've never used it, and i'm not sure i would. i haven't looked at it to examine it, though.
i've tried using it, but find it to be more trouble than it's worth. by the time i refresh my memory on how it works, i'd be better off using beam and column tables plus the ch. h equations to do the job.
the first time i saw those, my impression was that they were a total waste of space. after trying to use them, i still think that. i've heard them praised by a couple of the higher up aisc guys, so i'm sure they're not going anywhere.
i use them all the time - but maybe not quite as intended. there are incredibly useful in my opinion in two ways.
1. to get an exact value of the moment strength of a beam at a certain unbraced length in lieu of trying to follow it through the chapter 3 unbraced length graphs.
2. to get compression strength values for members that are not generally in the chapter 4 column tables.
examples:
1. find phimn of w21x44 with 20' unbraced length:
phimn = (8/9)*(1/the bx value in the chapter 6 tables). from p6-49, bx = 8.46*10^-3. so (8/9)*(1/0.00846) = 105ft-k
2. find the axial strength of a w18x40 unbraced for 15' in both directions.
phipn = (1/the p value in the chapter 6 tables).
from p6-57, p=7.56*10^-3. so (1/0.00756) = 132.3kips.

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