Need a book? Engineering books recommendations...

# Re: Torsional Constant

• To: seaint(--nospam--at)seaint.org
• Subject: Re: Torsional Constant
• From: Eric Ober <eric(--nospam--at)cagley.com>
• Date: Tue, 25 Feb 2003 13:56:37 -0500

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
njineer(--nospam--at)att.net