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Re: Torsional Constant

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I believe that, as an approximation, take the sum of bt^3/3 of all the component rectangular parts (like for concrete torsion constant) where 't' is the thinner dimension.  So J for you would be 0.14 in^4 I believe.  On a wide flange, you lose the fillets this way, but it's close enough usually.

Eric Ober

Nels Roselund, SE wrote:
I'm using Section F1 of the AISC Manual, 3rd edition, to analyze a 3/8" x 8" rectangular plate in bending about its major axis: it is subject to lateral torsional buckling.
J is defined as the torsional constant.  Where is the method of determining the value of J stated in the manual?  J is the polar moment of inertia of a section in "Roark's Formulas for Stress and Strain" -- is that also the definition of J used here?
Nels Roselund
Structural Engineer
South San Gabriel, CA