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# RE: Torsional Constant

• To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
• Subject: RE: Torsional Constant
• From: "Scott, William N." <William.Scott(--nospam--at)veco.com>
• Date: Tue, 25 Feb 2003 10:59:04 -0900

```See Boresi, 5th Edition "Advanced Mechanics of Materials" Section 6, Page
251 for torsion of rectangular sections.

J = k1*(2b)*2h)^3,

where
k1 is found from Table 6.1,
b is 1/2 of section height
h is 1/2 of section width

theta (rotation) = T/{k1*G*(2b)*2h)^3}
tau (shear stress) = T/{k2*(2b)*(2h)^3}

Table 6.1

b/h    1    1.5    2    2.5    3    4    6    10    infinite
k1    .141    .196    .229    .249    .263    .281    .229    .312    .333
k2    .208    .231    .246    .256    .267    .282    .299    .312    .333

-----Original Message-----
From: Nels Roselund, SE [mailto:njineer(--nospam--at)att.net]
Sent: Tuesday, February 25, 2003 7:04 AM
To: seaint(--nospam--at)seaint.org
Subject: Torsional Constant

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 <mailto:njineer(--nospam--at)att.net>

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