Experimental investigation on withdrawal resistance performance of nails in southern pine

Abstract

The objective of this study is to evaluate the structural performance and withdrawal capacity of three types of nails embedded in southern pine (SP) framing members. Pull-out tests on 430 specimens were conducted until complete withdrawal occurred. Representative variables derived from practical wall-to-wall or wall-to-floor connections were considered, including nail type, nail diameter, embedment length, and nail direction. Results reveal that the failure modes of specimens depend on nail shank roughness. Smooth shank nails (SSNs) and concrete nails (CNs) mainly experience nail-wood interface sliding and wood fiber tearing failures, while zinc-coated helically threaded nails (ZHTNs) exhibit wood fiber shearing and tearing failures. As expected, the ultimate withdrawal capacity increased with greater embedment length, with the highest capacity of nails in the perpendicular-to-grain direction, followed by parallel-to-grain. The withdrawal load-slip relationships of nails in SP consist of three stages: linear-elastic rise, plunge, and failure stage for SSNs and CNs, while ZHTNs exhibit elastic-plastic behavior during the second phase. The modified Rafi model suggested in this study can be used to translate the withdrawal bond-slip relationships of nails in SP. Finally, a withdrawal resistance calculation equation for SP was put forward and validated, showing an average difference of 10.33% between theoretical and experimental values.