Tension-Tree: Digitally fabricated connection for cross laminated timber construction

Cross laminated timber (CLT) construction is an emerging mass timber system whose performance depends strongly on connection design, particularly stiffness, strength, and ductility. This article introduces and characterizes a novel hold-down connection for CLT construction, termed Tension Tree . The connection integrates digitally fabricated interlocking timber elements with threaded rods and a steel plate. The rods provide a mechanically coupled inter-story load path for the tensile forces generated at wall boundaries, and the plate distributes these forces into the interlocking timber geometry. By studying the force-transfer mechanism, an analytical framework is proposed, and four prototype configurations are designed. Key geometric design parameters are further examined using finite element analysis to compare force transfer and stress distributions among the candidate configurations. The prototypes are then physically fabricated from 3-ply and 5-ply CLT panels using industrial computer numerical control (CNC) milling machines. They are tested experimentally in a series of pilot and replicate campaigns at 1:1 scale. Performance is evaluated using both quantitative and qualitative metrics. Results show that the proposed connection achieves high monotonic deformation capacity through controlled flexural and shear deformation of the interlocking elements, timber-steel interaction, and deformation of steel components. Overall, the connection provides a high-capacity solution and highlights the potential of digital fabrication to enable geometry-controlled timber connections.