Group Effect on In-Plane Shear Performance in Wooden Nail Connections

Cross-Laminated Timber (CLT) is ideal for tall timber structures but relies on environmentally concerning chemical adhesives. Nailed Cross-Laminated Timber (NCLT) offers a sustainable alternative by using densified wooden nails that form eco-friendly, adhesive-free bonds through lignin’s thermoplastic properties. However, significant uncertainties remain regarding the synergistic effects of multiple wooden nails. To address this, this study systematically analyzed the impact of the group effect on the mechanical performance of wooden nail joints. The results show that within the elastic range, the number of wooden nails has no significant effect on the elastic behavior of a structure. However, it is significantly positively correlated with both the joint yield load and yield displacement, enabling the accurate prediction of the structural yield point based on the number of wooden nails. With consistent nail arrangements, the group effect coefficient for the load-bearing capacity remains highly stable and shows no significant correlation with the number of nails. Additionally, an increase in the number of wooden nails significantly enhances the deformation resistance and structural stiffness, while having a minimal impact on ductility. This study reveals the linear additive nature of the group effect in wooden nails, providing important theoretical support for the design of NCLT.