Experimental and finite element studies of 3D-printed concrete-glued laminated timber composite beams

This study investigates a composite beam structure system combining glued laminated timber (GLT) and 3D-printed concrete (3DPC), which employs a notched-screw connection filled with ultra-high-performance concrete. Experimental results indicate that the distance from the beam end to the connection should be increased to prevent shear failure of the timber at the beam ends. Increasing the height of the 3DPC slab from 110 mm to 150 mm improves the overall stiffness and load-bearing capacity of the beam. With the incorporation of polyoxymethylene fibers, the material demonstrates ductile fracture behavior. Furthermore, the use of polyethylene fibers notably improves the ductility of 3DPC while also providing significant enhancement in crack resistance. Parameter analysis shows that increasing the height of the GLT beam is the most effective measure for enhancing both load-bearing capacity and stiffness, resulting in a maximum improvement of 43 %. The spacing between connections can be reduced to effectively improve the combination efficiency. An increase in the GLT strength grade enhances the load-bearing capacity but reduces ductility. In the serviceability and ultimate limit states, composite beams incorporating UHPC notches and screw connections exhibit composite action coefficients of approximately 78 % and 68 %, respectively. Compared with existing similar connection details, this configuration shows enhanced composite efficiency. To address the overestimation of bending stiffness by the γ method, this study validates a modified model that accounts for the non-uniform strain distribution induced by axial forces. Finally, regarding the bending failure mode at the bottom of the GLT beam, a formula for calculating the ultimate load-bearing capacity was established.