Geometry-Driven Parametric Modeling of Reinforcement in Variable-Section Special-Shaped Columns Using BIM

Automated reinforcement modeling of variable-section special-shaped columns remains challenging because sectional variation simultaneously affects longitudinal-bar trajectories and stirrup configurations. This study proposes a geometry-driven parametric BIM method in which section dimensions and reinforcement-detailing parameters are mapped to reinforcement control points. Longitudinal bars in stable regions are represented by two endpoints, while those crossing the transition region are described using multi-control-point trajectories. Stirrup coordinates are updated with elevation to maintain geometric compatibility with inclined longitudinal reinforcement. The method was implemented in Autodesk Revit 2020 using C# and the Revit API and applied to L-, T-, cross-, and Z-shaped variable-section columns. Quantitative validation showed a mean spatial deviation of 0.161 mm across 264 representative control points, while the proposed workflow achieved a mean case-specific modeling-time reduction of 93.03% compared with conventional manual modeling. Reinforcement length and quantity outputs were also consistent with independent calculations. An engineering application further illustrated the use of the proposed workflow in a practical project context. The proposed framework provides an efficient and extensible approach for coordinated reinforcement generation and BIM-based information output in regular variable-section special-shaped columns.