Reciprocity in craftsmanship: Advancing rup-rup bamboo bending through parametric design

The rup-rup technique is a traditional incision-based method for bending bamboo culms that relies on tacit craftsmanship and material feedback rather than formalized geometric rules. Although recent computational studies have modeled rup-rup using curvature-based segmentation, most approaches assume uniform culm geometry and do not account for longitudinal variability in internode spacing and diameter fluctuation. This study develops a material-informed parametric framework that translates tacit craft heuristics into rule-based computational logic while integrating culm-specific geometric data. An experimental–computational methodology was employed, combining craft observation, manual geometric measurement of twenty-one Gigantochloa apus specimens, parametric scripting in Rhinoceros/Grasshopper, and full-scale bending experiments. Two computational models were evaluated against traditional practice: a curvature-driven Tangent-Curve Method and a craft-informed Length-Differential Method. Each model was tested with and without incorporation of literature-based elastic parameters. Results indicate that generalized morphological datasets were insufficient for accurate curvature prediction, whereas element-specific geometric input significantly improved bending accuracy and reproducibility. Furthermore, stabilizing cut width within the parametric logic reduced operator-dependent variability while preserving adaptive material response. The findings demonstrate that computational formalization does not substitute craftsmanship but redistributes decision-making by encoding geometric consistency while maintaining material sensitivity. The proposed framework advances material-aware parametric modeling for non-uniform natural materials and contributes to hybrid digital–craft design methodologies in architectural computation.