Lateral resistance of ring-shank nail connections in Southern Pine lumber

Abstract

The goals of this research were to gain a better understanding of the performance of ring-shank (annularly threaded) nails in lateral connections common to the post-frame industry, and to evaluate the European yield model (EYM), the basis for derivation of allowable design values, for ring-shank nails. Inputs to the EYM include nail bending yield strength, dowel bearing strength, and connection geometry. These parameters as well as single-shear connection strength were determined for nine nail groups tested in Southern Pine lumber. Nail specimens included three suppliers, two shank types (smooth and ringshank), two diameters (3.76 and 4.50 mm), and two coatings (galvanized and ungalvanized). Ring-shank nails averaged 85% higher nail bending yield strength than the common nails for all but two groups. A regression model relating dowel bearing strength to specific gravity was developed based on tests with the nine nail groups loaded parallel-to-grain in Southern Pine. A statistically significant reduction in dowel bearing strength was observed for 4.50 compared to 3.76 mm diameter nails. While ring-shank nail connection maximum loads were roughly twice that of common nails for the same diameter, no significant differences were observed for yield loads. The current yield load definition is based on the slope of the initial portion of the load-displacement curve and does not adequately account for increases in connection strength resulting from higher steel quality. As a result, predicted yield loads based on the EYM were significantly higher than observed yield loads. A revised yield load definition is needed which includes yielding predicted by the EYM without including factors extraneous to the model. Ring-shank nails exhibited significantly higher lateral connection strengths than the common nails tested as a result of increased steel strength and gripping action of the threads. Finally, standardization in ringshank nail manufacturing must be instituted to ensure minimum steel and thread quality, before any increase in design values for ring-shank nails is implemented.