Experimental investigation on the mechanical performance of 3D-printed concrete-glued laminated timber composite beams

This study presents a novel, reinforcement-free prefabricated composite beam system integrating 3D-printed concrete (3DPC) slabs and glued laminated timber (GLT) beams. The system employs an ultra-high-performance concrete (UHPC)-filled notch-screw shear connector to address the interfacial bonding challenge between the two materials. Push-out tests on the connector demonstrated that its load-bearing capacity and slip stiffness increased with notch depth and length, while the shear length ahead of the notch had a minor influence. For the critical 3DPC-UHPC interface, three failure modes were identified, with performance governed by matrix interlayer properties and interface morphology. The X-interface with an original 3DPC surface was optimal, and adding polyoxymethylene fiber further enhanced performance. Connectors with a vertical printing path showed superior performance, with approximately 8% higher load capacity than those with a horizontal path. Bending tests on composite beams clarified the influence of cross-sectional mesh configuration and printing material. Beams with a transverse mesh exhibited 28.8% greater initial stiffness than those with a top-surface mesh. Crucially, the system achieved satisfactory structural performance without traditional steel reinforcement, validating the feasibility of the proposed reinforcement-free, prefabricated approach. Finally, predictions for bending stiffness and interface shear capacity based on the gamma method showed good agreement with experimental values.