Table 12.2F: Head pull-through design values
through provisions. Within the range of head diameters, thicknesses, and specific gravities in the NDS, the analysis found that head pull- through is related to the perimeter of the fastener head. For the design of roof sheathing fastening to resist wind uplift, the addition of head pull-through allows the controlling roof sheathing fastener spacing to be calculated from the lesser of the head pull-through design value or the fastener withdrawal design value from wood in accordance with the NDS. Previously, such design required use of a combination of design documents, including minimum prescribed spacing criteria for wood panels (see Table 12.2F). • Revised provisions for specifying diameter for threaded nails: A change in ASTM F 1575 Standard Test Method for Determining Bend- ing Yield Moment of Nails clarifies that nail bending yield strength, F yb , is based on the nominal diameter, D, not on the root diameter, D r . This change allows simplification of the calculation of nail moment resistance in the NDS yield equations for nails specified in F 1667 because D is provided for all nail types, but D r is not always provided for deformed shank nails. As a result, the revised NDS provisions al- low the use of D for deformed shank nails per F 1667 when calculating lateral design values in accordance with the yield limit equations. NDS Supplement It is also worth noting that NDS Supplement design values remain unchanged with only a few exceptions. New and revised grades of machine stress-rated lumber and machine evaluated lumber have been added. Redwood grades requiring “close grain” were removed due to general lack of availability for commercial use. Other revisions include the addition of Norway Spruce from Norway to foreign species di- mension lumber, and the addition of shear-free moduli of elasticity for structural glued laminated softwood timber (glulam).
Conclusion To make this code-referenced standard as user friendly as possible, AWC will also be developing supporting publications such as an NDS Commentary, revising technical reports and design aids, and conduct- ing further research to ensure continued widespread acceptance of wood in construction. The 2018 NDS and 2018 NDS Supplement: Design Values for Wood Construction are currently available online as free electronic down- loads in PDF format (www.awc.org/codes-standards/publications/nds- 2018). The NDS Commentary and other support documents will be available in the coming weeks as part of AWC’s “2018 Wood Design Package.” At that time, print versions of the 2018 NDS with Com- mentary and 2018 NDS Supplement, as well as printable PDFs, will be available for purchase. In the meantime, AWC thanks the volunteers on our Wood Design Standards Committee for their work on this important publication. The 2018 NDS represents the state-of-the-art for design of wood members and connections. BRAD DOUGLAS, P.E. , is vice president of engineering at the American Wood Council (AWC; www.awc.org), which represents the interests of the North American wood products industry. On behalf of the industry it represents, AWC is committed to ensuring a resilient, safe, and sustainable built environ- ment. To achieve these objectives, AWC contributes to the development of sound public policies, codes, and regulations that allow for the appropriate and responsible manufacture and use of wood products.
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