at the middle of each side

Regular hexagon

Regular hexagon

0.217 Ad

0.133 Ad2G

where d is the diameter of inscribed circle and A is the cross-sectional area

'From S. Timoshenko. Strength of Materials. Part II, Advanced Theory and Problems, Van Nostrand, New York, p. 235. Approximate angles of twist for other solid cross-sections may be obtained by the substitution of an equivalent elliptical cross-section of the same area A and the same polar second moment of area J. The relevant equation for the elliptical section in Table 5.2 may then be applied.

can be constructed within the cross-section touches the section boundary - see Fig. 5.5. Normally it occurs at the point where the curvature of the boundary is algebraically the least, convex curvatures being taken as positive and concave or re-entrant curvatures negative. The maximum shear stress is then obtained from either:

or where, for positive curvatures (i.e. straight or convex boundaries),

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