structures + buiLdings
What the 2018 IBC means for wood construction: Part I American Wood Council updates its 2018 National Design Specification. By Brad Douglas, P.E.
Following availability of the International Code Council’s 2018 International Building Code, the AmericanWood Council updated its National Design Specification (NDS) for Wood Construction
When it comes to modernizing building codes and standards, ensuring the buildings in which we live and work are safe is a top priority for the American Wood Council (AWC). AWC experts work to achieve this through ongoing research and development of design standards and guidelines that demonstrate how wood products can safely and ef- ficiently meet or exceed U.S. requirements. With technological advances and material innovations regularly affect- ing the use of wood products, AWC is committed to ensuring these changes are accurately reflected in the codes and properly implemented by industry professionals. Now that the International Code Council’s 2018 International Building Code (IBC) is available for enforcement, AWC has updated its National Design Specification (NDS) for Wood Construction (http://awc.org/codes-standards/publications/nds-2018) accordingly. The 2018 NDS was developed by AWC’s Wood Design Standards Committee and is referenced for wood design in the 2018 IBC. It has been approved as an American National Standard by the American National Standards Institute (ANSI). Significant additions to the 2018 NDS include new Roof Sheathing Ring Shank nails and fastener head pull-through design provisions to address increased wind loads in ASCE 7-16 Minimum Design Loads and Associated Criteria for Build- ings and Other Structures.
More specifically, changes in the 2018 NDS include: • allowance for incising factors for specific incising patterns and lumber sizes when obtained from the company providing the incising; • inclusion of a volume factor for structural composite lumber tension parallel to grain values; • inclusion of effective shear stiffness for cross-laminated timber; • added equation for withdrawal design values for smooth shank stainless steel nails; • new provisions for Roof Sheathing Ring Shank (RSRS) nails in accor- dance with ASTM F 1667; • new design provisions for fastener head pull-through of fasteners with round heads; • revision to method for calculation of lateral design values for threaded nails to be based on use of shank diameter instead of root diameter in accordance with changes in ASTM F 1575; • revised timber rivet design value tables to limit maximum distance per- pendicular to grain between outermost rows of fasteners; and • revised terminology for Fire Design of Wood Members to clarify the difference between “char depth” and “effective char depth” used in structural calculations. Provisions for connections is also revised to more precisely describe the requirements for protection of the connec- tion from fire exposure.
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march 2018
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