Influence of repeated wetting and drying on withdrawal capacity of wooden nails and metal nails

Abstract

Metal nails pose inherent safety risks to wood structures due to their susceptibility to moisture-induced rusting. Currently, densified wooden nails create an opportunity to replace metal fasteners with renewable materials, so the durability of wooden nail joints is crucial for the stability of wood structures. This study investigated the withdrawal resistance and corrosion resistance of densified wooden nails (gun-driven and manual-driven) and low-carbon steel nails (smooth shank and helical shank) when inserted on Chinese fir(Cunninghamia lanceolata (Lamb.) Hook.) specimens following repeated wet-dry cycles, aiming to provide scientific evidence for the engineering application of densified wooden nails. The results demonstrated that among the untreated samples, gun-driven wooden nails exhibited the highest withdrawal strength, surpassing manual-driven nails by factors of 4.16 (wooden nails), 3.19 (smooth nails), and 1.24 (helical nails). However, following the wet-dry cycles, the withdrawal strength and withdrawal energy of gun-driven wooden nails experienced significant reductions, but no obvious corrosion traces were found on the nail surfaces. Although the mechanical properties of smooth nails were obviously increased, the degree of corrosion was the most serious. In contrast, the mechanical properties of manual-driven wooden nails and helical nails remained relatively stable. Except for cycle-0, all types of nails displayed small stiffness fluctuations throughout the wet-dry cycles.