Parametric Detailed Design for Complex Spatially Bending-Torsion Steel Members Based on the Grasshopper Platform

The proliferation of free-form architecture necessitates efficient detailing methods for complex spatially bending-torsion steel members. Current approaches suffer from low modeling efficiency, inaccurate surface fitting, and limited capabilities for variable-section generation and plate unfolding. This study presents a comprehensive parametric detailing module developed within the Grasshopper (GH) platform to overcome these challenges. The core innovations include (1) a data structure that integrally describes member axes, cross-sections, and unfolding information; (2) an algorithm that automatically generates interpolation points based on curvature variation to ensure axis smoothness; (3) the use of architectural surface normals as member torsion vectors, eliminating manual control point placement; and (4) integrated alignment and unfolding functions for fabrication-ready outputs. In an engineering case study, the module reduced modeling time by approximately 70% compared to conventional methods while achieving a root-mean-square deviation of less than 2 mm between the fitted and target surfaces. The system enables rapid generation of 3D models and 2D fabrication drawings for complex bending-torsion members, significantly enhancing detailing efficiency and precision.