Implementation of Torsional Capacity Checks for NZS 3404:1997 Steel Code

Currently, while STAAD.Pro accurately calculates torsional analysis results (Mx) during the solver phase, the NZS 3404 design engine skips automated member resistance and capacity checks for torsion. This forces engineers practicing in New Zealand to manually extract forces and run external spreadsheet verifications for open and closed sections experiencing torsional demands.We request that the development team brings the NZS 3404 design module to parity with codes like AISC 360 and EN 1993 by implementing the following:

1. Pure Torsion Capacity Checks: Automated calculation of torsional capacity (phi * Tu) for standard open sections (Universal Beams, Welded Beams, Channels) and closed sections (CHS, SHS, RHS) based on Section 8 of NZS 3404 and its accompanying commentary.

2. Combined Actions Design: Proper integration of torsional shear and warping stresses into the combined axial, bending, and shear interaction equations where required by the standard.

3. New Design Parameters: Introduction of user-controlled parameters (similar to the TORSION parameter in the Eurocode engine) to allow users to toggle torsion tracking on or off depending on whether the torsion is primary or secondary.

As NZS 3404 remains the primary legal compliance pathway for steel design under the New Zealand Building Code (B1/VM1), having native torsional design capabilities would significantly improve workflow efficiency and safety for New Zealand engineering firms relying on STAAD.Pro.