In an earlier paper, a method was presented for the simplified analysis of frame-tube structures under bending actions. By replacing the discrete structure by an equivalent orthotropic tube, and by making simplifying assumptions regarding the stress distributions in the structure, design curves were derived for rapid approximate analysis of the dominant behavior. A similar analysis is presented in this paper for the torsional analysis of frame-tube structures. Closed-form solutions are obtained and design curves are developed for three standard torsional loading cases, corresponding to those considered in the bending analysis, i.e., a point torque at the top, and uniformly and triangularly distributed twisting moments, Design curves are found to be identical in form to those derived for the bending case.