Aluminium Design and Construction John Dwight

For sections where the position of the shear-centre S is known, equation
(10.29) enables H to be found directly. For other sections, it is first
necessary to locate S.
10.5.5 Bisymmetric and radial-symmetric sections
For these, S lies at the point of symmetry, which is also the point of
zero warping. We take O at the same position, giving wo =0.
For the bisymmetric case (Figure 10.17(a)), the elements are numbered
in one quadrant only. The necessary summation in equation (10.29) is
then made just for these elements, and the result multiplied by 4 to
obtain H. Note that element 1 makes no contribution because it does
not warp.
Figure 10.17(b) shows the radial-symmetric case, consisting of n equally
spaced identical arms, each symmetrical about a radius. For this, the
summation in equation (10.29) can be made for the elements lying one
side of one arm, and the result then multiplied by 2n.
Figure 10.17 Symmetric sections: (a) bisymmetric; (b) radial-symmetric; (c) skew-symmetric;
(d) skew-radial-symmetric.
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