C-G5G5 Round HSS

Little information is available on round HSS subjected to transverse shear; therefore, the recommendations are based on local buckling of cylinders due to torsion. However, because torsion is generally constant along the member length and transverse shear usually has a gradient, it is recommended to take the critical stress for transverse shear as 1.3 times the critical stress for torsion (Brockenbrough and Johnston, 1981; Ziemian, 2010). The torsion equations apply over the full length of the member, but for transverse shear it is reasonable to use the length between the points of maximum and zero shear force. Only thin HSS may require a reduction in the shear strength based upon first shear yield.

In the equation for the nominal shear strength, $V_{n}$, it is assumed that the shear stress at the neutral axis, $V Q / I b$, is at $F_{c r}$. For a thin round section with radius $R$ and thickness $t, I=\pi R^{3} t, Q=2 R^{2} t$, and $b=2 t$. This gives the stress at the centroid as $V / \pi R t$, in which the denominator is recognized as half the area of the round HSS.