T T

L k2db*G JeqG

where Z' is the torsion section modulus

= Z' web -(- Z' flanges = k\d\b2 + k\d2b\ + ... etc.

and Jeq is the "effective" polar moment of area or "equivalent J" (see §5.7) = J eq web + /eq flanges = k2d\b\ + k2d2b\ + ■ ■ ■ etc. = Y,k2db3

and for d/b ratios in excess of 10, k\ = k2 = so that

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