Primary changes in the 2018 WFCM include: • Updated design load standard reference from ASCE 7-10 to ASCE 7-16 Minimum Design Loads and Associated Criteria for Buildings and Other Structures. • Revised “Basic Wind Speeds for One- and Two-Family Dwellings” figure based on three-second Gust Basic Wind Speeds for Risk Category II Buildings to coordinate with updated reference to ASCE 7-16. • Added requirements for identification and description of wood structural panels to recognize “Performance Category” consistent with the IBC. WFCM references to wood structural panel (WSP) thickness appear in several forms. References to WSP thickness were revised throughout the standard to consistently describe wood structural panels and more accurately describe thickness as a nominal value to coordinate with changes to Section 1.2.1.8 and the codes. For example, 15/32-inch WSP becomes Nominal 15/32-inch WSP; 7/16-inch becomes Nominal 7/16-inch; and Minimum Panel Thickness (inches) becomes Minimum Nominal Panel Thickness (inches). • Revisions to coordinate with ASCE 7-16’s increased roof uplift require- ments due to changes in localized roof wind design pressures and ad- dition of lower wind speed categories (e.g. 90, 95, 100, and 105 mph). • Addition of roof rafter uplift tables to provide roof uplift requirements and maximum spans for roof rafters in accordance with ASCE 7-16 localized roof wind design pressures. • Incorporation of fastener criteria from AWC’s 2018 NDS to include pro- visions for roof sheathing ring shank (RSRS) nails and fastener head pull-through design values.
• Clarification of terminology used for rake overhangs and limit of rake overhang lookout blocks to 9 inches based on increased roof uplift requirements due to localized roof wind design pressures (see Figures 1 and 2). • Revised “Shear Wall Assembly Allowable Unit Shear Capacities,” “Maximum Shear Wall Segment Aspect Ratios,” and “Sheathing Type Adjustments” tables to incorporate updated aspect ratio adjustments consistent with AWC’s 2015 Special Design Provisions for Wind and Seismic (SDPWS). • Revised “Roof Sheathing Attachment Requirements for Wind Loads” table to give common, box, and RSRS nail size and sheathing options by includ- ing requirements for uplift load per nail and fastener uplift capacity. Visit www.awc.org/codes-standards/publications/wfcm-2018 to down- load a free version of the 2018 WFCM in PDF format, see more details regarding changes, and view a recent webinar to obtain free education credits. A print version of the standard is expected to be available for purchase in the coming months. 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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csengineermag.com
may 2018
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