huangyhg

strong axis plate bending
first off, i rarely design in steel (and haven't really since college), and i'm not all that familiar with the aisc manual. my somewhat hypothetical question is this (and referencing the aisc-asd 9th ed, since that is the one i have):
suppose i have a cantilever steel plate with a point load at the end acting in the strong axis direction. assume a 100" long beam, 10" deep, and 1" wide. say a 1-kip load acting at the free end and in the 10" direction. therefore, a 100 kip-in moment at the base. using the 9th ed aisc, what do you check for/against? compact/noncom/slender of a "web"? there are no flanges, it's not an outstanding leg, and it's not supported along a single edge, right? fb=0.6*fy and use sx of the rectangular section? fb=0.75*fy due to additional strength associated with shape factor (but it's not restrained by a flange/web connection)? is there a specific lateral torsional buckling calculation to be done? it seems that eventhough an allowable fb may be calculated using 0.6*fy, that could potentially be limited by some sort of out of plane bucking of the (long)x(tall)x(thin) plate. true or not?
ideas, opinion, past experience are welcome. thnx.
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the aisc 9th ed. does not cover plates bending about the strong axis. you need the 13th edition. i'm not sure this information is even in the 3rd lrfd ed. either but i would have to check to be sure. other wise you're looking at plate buckling analysis using mechanics of materials, theory of elasticity or fem.
the 2005 aisc steel specification is a free download from the aisc. the manual itself is very expensive. you can find the download here. look in section f11.
my aisc manual is the 8th edition ... like i said, i'm a dinosaur.
i think your question is answered by pointing out that your flanges (non-existent) do not meet the criteria necessary to stiffen the section against ltb.
for particulars, refer to section 5, article 1.5.1.4 bending. there is a list of criteria that begin with a requirement that the flange shall be continuously connected to the web or webs.
as ucfse pointed out, for this geometry you should check a book on plate buckling. also, when the d/l gets too large, you start to have effects from shear deformation not normally considered. i recommend timoshenko, theory of buckling, for further information. good luck
i think the allowable bending stress in a case like this is 0.6*fy*q, with q being based on the local buckling criteria in chapter b in the 9th edition of aisc.
daveatkins
by the 2005 chapter f11, it looks like local buckling is not a consideration.
it seems intuitive to me that it'll be the ltb limit state and not a bending or local buckling issue. when you run the numbers from the 13th, this works out.
thanks for the input. i figured it should be a ltb limit, but it was unclear how to quantify/justify the limit using the aisc specs/appendices without flanges (referencing the q factor). i just downloaded the 2005 spec, and i'll give sect f11 a read.
on a side note, this is a great forum. i've browsed this site for the past 5 years for ideas and opinions, but this was my first time posting a question. thanks.

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