Conformal 3D printing on bending-active formwork: Fabrication methods and structural implications for wide-spanning concrete structures

This paper presents an integrated approach to the design, fabrication, and structural analysis of wide-spanning concrete structures by combining bending-active formwork with conformal 3D printing. Traditional large-scale additive manufacturing in construction is constrained by horizontal layer deposition, limiting applications to vertical elements such as walls. To extend 3D printing capabilities to roofs, floors, and other spanning elements, this study proposes using elastically deformed timber strips as lightweight formwork substrates onto which concrete is robotically deposited along non-planar, structurally informed toolpaths. The methodology is validated through a systematic experimental campaign progressing from material characterization and small-scale tests to a full-scale prototype spanning 4.6 meters. Complementing the physical investigations, a voxel-based finite element simulation framework is developed to evaluate the influence of toolpath strategies and interlayer timing on structural stability during the printing process. Results demonstrate that toolpaths aligned with the global span reduce formwork buckling and promote uniform stress distribution, while short interlayer pauses enhance printing stability. This research contributes a novel fabrication and analysis framework for sustainable, material-efficient construction of curved, long-span architectural elements.