QUESTION: (SUMMER2015) How are the torsional constants calculated for open sections in the CISC Handbook? Using general strength of material formulas, I can reproduce the values for angles, but I obtain different values for other shapes.

ANSWER: Torsional section properties found in the Handbook include the St. Venant constant (J) and the warping constant (Cw). General formulas do not usually incorporate the contributions of the round fillets at the intersection of the web and flange(s) in open sections, as shown in Figure 1. The fillets are not taken into account for angle sections, but they are included for other open sections such as wide flange and Tee shapes.

While the warping constant is not significantly affected by the fillets, the St. Venant constant is significantly increased, and calculations in the Handbook are based on the following reference: El Darwish, I.A. and Johnston, B.G. 1965. Torsion of Structural Shapes. ASCE Journal of the Structural Division, Vol. 91, ST1. (Errata: ASCE Journal of the Structural Division, Vol. 92, ST1, 1966)