Restrained warping for the torsion of thin-wall open sections is not included in most commonly used frame analysis programs. Almost all frame programs in practice use St-Venant torsion theory ignoring the effects of restrained warping.

Torsion and warping

It is important to note that the torsional stiffness of an open section is function of the warping end conditions as well as the location of the torsional load. Thus, the distribution of the forces in the structure having members resisting torsion may differ whether this option is enabled or disabled. A subdivided continuous member needs to be specified as a physical member to get the continuity effect of warping along the member.


In addition to shear stresses, some members carry torque by axial stresses. This is called warping torsion. This happens when the cross-section wants to warp, i.e., displace axially, but is prevented from doing so during twisting of the beam. In other words, the section tends to resist torsion by out of plane bending of the flanges.

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