Withdrawal capacity of plain, annular shank and helical shank nail fasteners inspruce-pine-fir lumber
Published: 2013
Publication Name: Forest Products Journal 63(5/6)
Publication URL: https://meridian.allenpress.com/fpj/article/63/5-6/213/136823/Withdrawal-Capacity-of-Plain-Annular-Shank-and
Abstract:
This study examines the withdrawal load and energy capacity of three types of nail fasteners that are commonly used to attach sheathing to framing members: 8d common, annular ring shank, and helical shank. A baseline set of data was collected for single nails in accordance with test methods defined in ASTM D1761. Tests were performed until complete withdrawal occurred in order to quantify the total withdrawal energy. The average peak loads from testing were within 7 to 8 percent of predicted values. The annular and helical nails had much higher peak load capacity as expected, and the withdrawal energy was also greater. A new device was developed in order to subject multiple nails to withdrawal loading simultaneously. Reinforced sheathing was used to transfer load from the hydraulic actuator to the nails, which is more representative of actual structural response where there is load sharing among the nails. This device allowed direct comparison with the single nail results. Further, it also allowed the examination of a stitched nailing pattern, where fasteners are driven at alternating angles of ±60° measured from the framing member face. It was found that the stitched pattern resulted in 42 percent higher peak load capacity per fastener for 8d common nails, but for the helical and annular nails, peak load was similar to that achieved with a normal 90° drive angle. Withdrawal energy was 24 to 48 percent higher for all nail types using the stitched pattern.
In roof and wall building systems, a sheathing panel’s ability to support negative pressures is mainly provided by the fastener resistance to withdrawal and pull-through (Sutt et al. 2008). In withdrawal and pull-through failures, withdrawal refers to the fastener withdrawing from the framing members, and pull-through refers to the head of the fastener pulling through the sheathing. The resistance of a nail to withdrawal from wood-based materials is characterized by several factors, including framing member material density and moisture content/conditioning, nail shank diameter, and the depth of penetration (US Department of Agriculture [USDA] 2010). The resistance to nailhead pull-through in sheathing is influenced by similar factors, including material density and conditioning, as well as other factors, such as nailhead diameter and the sheathing thickness (Herzog and Yeh 2006).
Several nail types designed to increase nail withdrawal capacityincluding ring shank and helically threaded shankhave been developed. When comparing annular and helically threaded nails in spruce-pine-fir (SPF) at 12 percent moisture content, Rammer et al. (2001) found no significant difference in mean withdrawal strength. The Wood Handbook, Chapter 8, Fastenings (USDA 2010) provides peak withdrawal values for annular, helical, and common nails but indicates the peak withdrawal load can vary significantly from nail to nail depending on the shank’s surface coating or even the type of chemical residue present after production. Based on these observations, the Wood Handbook only presents nail performance up to and for a limited displacement postpeak. Previous testing and development of reference design values are based on single fastener withdrawal standard test methods per ASTM D1761 (ASTM International 2006) and do not consider the simultaneous loading of multiple fasteners. The current reference design value for multinail connections is the sum of the individual fastener design values (American Forest & Paper Association [AF&PA] 2005), which may produce a nonconservative design value for panels under negative pressure (Sutt et al. 2008). In most cases the connection designer must make judgment decisions regarding pull-through resistance, potential load sharing between fasteners, and the actual capacity of annular and helical shank nails (Sutt et al. 2008).
The objective of this study was to assess the relative withdrawal capacity of annular, helical, and smooth shank nails in single nail and