14 pages (227 KB PDF)
In the 2001 and 2005 National Design Specification® (NDS®) for Wood Construction, calculation of reference lateral design values for lag screws and wood screws will typically require use of the fastener root diameter, Dr, unless a more detailed analysis is performed to account for the varying moment and bearing resistance of the fastener (NDS Section 11.3.2). One alternate method of accounting for the moment and bearing resistance of the threaded portion of the fastener and moment acting along the length of the fastener is provided in AWC's Technical Report 12 (TR12) - General Dowel Equations for Calculating Lateral Connection Values.
Example calculations in this Design Aid are shown for lag screw connections; however, the design approach is also valid for wood screws. Example 1 addresses application of TR12 for three lag screw connections having identical side and main members but different screw geometry. Example 2 addresses calculation for the required length of unthreaded shank into the main member such that diameter, D, is applicable for calculation of reference lateral design values.