Wooden nail connections could outperform metal fasteners when optimised for factors like nail diameter, sheathing material, and spacing, greatly assisting in rapidly assembling timber parts in prefab construction.
That is according to a new Chinese study, which revealed that new and improved densified wooden nails could hold the key to improving the shear performance of timber walls and, importantly, offer a more durable and longer-lasting alternative to metal-based connectors.
The study, “Lateral Resistance Performance of Wall-Frame Shear Walls with Wooden Nail Connections: Experimental and Finite Element Analysis,” conducted a series of full-scale loading tests on structural-grade spruce-pine-fir (SPF) oriented strand board (OSB) and structural plywood (SF) samples, all with varying panel thickness, spacing, and cap configuration.
“Historically, metal fasteners like smooth nails, angle brackets and screws have been the go-to for connecting wooden components. However, their long-term durability can be compromised in environments with fluctuating humidity and temperatures,” according to the researchers led by Shuo Wang of the Nanjing Forestry University. “(At the same time), densified wooden nails have emerged as a more sustainable alternative, offering continuous production capabilities and better environmental compatibility.”
“By fine-tuning high-density thermosetting resin formulations and pneumatic gun technology, wooden nails can form strong chemical and mechanical bonds with wood,” the researchers said, adding that nail improvements also help automated assembly and enhance overall production efficiency. “This study assesses whether these connectors can hold their own in structural applications like wood-frame shear walls.”
Structural plywood and OSB were tested to the Chinese National Standards for timber.
Testing the structural-grade SPF lumber with different types of beech wooden nails, the researchers showed that larger nail diameters and thicker shearing panels led to a higher load-bearing capacity.
“Structural plywood sheathing outperformed OSB in terms of peak load and joint stiffness. (Crucially) the inclusion of nail caps and closer nail spacing further improved shear resistance with larger-diameter nails showing the best overall performance.”
According to the researchers led by Shuo Wang of the Nanjing Forestry University
According to Wang, the study provides strong evidence that carefully engineered wooden nail connectors can enhance the shear performance of timber joints. However, he cautioned, “(this) research was limited to monotonic loading, with additional studies needed to assess how connectors would perform under cyclic or extreme conditions.”
He said that future studies should explore other types of fasteners, including wood-based adhesives, and refine modelling techniques to account for dynamic loads, material aging, and moisture effects. “These steps will be essential for advancing the role of wood-based connectors in resilient, energy-efficient building systems.”
- To read more about the potential for hardwood-based dowels to replace metal fasteners in cross-laminated timber walls and floors, click here for Wood Central’s special feature from last year.
