Effect of Nail Models and Diameters on Withdrawal Strength of a Tropical Hardwood: A Preliminary Study

Nails are a simple and viable solution to connect sections of wooden structures. Although they are the oldest and most traditional connection elements, there is a considerable knowledge gap concerning the use of larger sized, threaded nails, in tropical hardwoods. The objective of this study was to evaluate the effect of different nail models and diameters on the withdrawal strength of Allantoma decandra wood and verify the efficiency of the existing prediction equations of nail withdrawal. Withdrawal tests were carried out using three nail models (smooth, helical, and annular), of two different diameters (2.8 mm and 3.5 mm). For each combination, ten A. decandra wood specimens were used. Four nails were inserted 32 mm into each wood specimen and then withdrawn using a universal testing machine with a 600 kN capacity, according to the procedures of ASTM D143 (2014). The nail model was the most relevant factor in this study, having a direct influence on withdrawal strength. Annular nails presented the highest strength values, followed by helical and smooth nails. The nail diameter had no significant effect on the maximum load result. The equations for withdrawal strength prediction demonstrated considerable accuracy regarding the experimentally obtained data, being important tools to anticipate the behavior of wooden structures.