If a section has a few holes or a short slot in it, it is still considered closed. These are sections like round bars and tubes. The traditional formulas for the polar moment of inertia work only for closed or continuous sections.
Traditional Polar Moment of Inertia Formulas The Polar Moment of Inertia can be used to calculate shear stress and torsional deflection.
Resistance to torsion is based entirely on the shape of the section and not the material properties. The Polar Moment of Inertia is a member’s ability to resist twisting from torsional loads. It didn’t take but 2 minutes for Marvin to set us straight the traditional formulas for torsion just don’t work on open sections. Now, it was time to summon to “old guy” to come help us out. We went back and calculated our torsional deflection again and found no issues. The torsional deflection was excessively high. Image is Public DomainĪ few weeks later, we starting running Finite Element Analysis on the design and the structure lit up like a Christmas tree! At first we thought it was an error in the loading, but we quickly realized the problem.
