Bamboo tenon-peg shear connectors for long-span mass timber composite floors: Experimental study and finite-element stress analysis

Mass timber products represent key materials in contemporary building design, supporting the transition towards a sustainable and circular construction economy. In mass timber construction, connections govern system-level structural performance and material efficiency. This study shows a new material design framework for long-span cross-laminated timber (CLT)-glulam composite flooring systems, incorporating bamboo-based tenon and peg connectors fabricated using computer numerical control (CNC) machining as an alternative to standard mechanical joints. Push-out shear tests were conducted to characterize the mechanical properties and failure modes of two variants of shear connectors: i) with parallel strands bamboo (PSB) used as tenons and pegs, and ii) with PSB used as tenons and laminated bamboo lumber (LBL) as pegs. The mean load-carrying capacities were 111.07 kN and 106.40 kN per shear plane for the PSB-PSB and PSB-LBL groups, respectively. Within the 6 replicas tested, governing failures were bending and local material crushing in the tenons and CLT lamella, respectively. A 3D mechanics-based finite-element model was developed in ANSYS to map stress and deformation distributions in proximity to the bearing areas, particularly along the mortise perimeter. The model incorporated cohesive zone material properties to capture damage evolution and nonlinearities and was validated against the load-slip experimental curves. The findings confirmed that local mortise deformation influences stiffness but does not compromise peak loads of the tested shear connectors. The stress analysis on the four identified local areas shows that the CLT innermost lamella has significant contribution to the joint’s capacity at a large slip (30 mm). Relating to the pre-design formulations, the joint load-carrying capacity is related to the actual shear plane location on the tenon; however, the possibility of local buckling on the CLT innermost layer is also necessary for ultimate load check. These results support alternative design options for timber joints in mass timber construction, enabling the integration of bio-based materials into large-scale composite floor fabrication for a more sustainable built environment.