Does the penetration depth factor, C_d, apply to design values for lag screws, wood screws, or nails?
The 1997 National Design Specification® (NDS®) for Wood Construction (and 1996 LRFD Manual) only required the designer to check 3 yield mode equations for screwed and lag screwed connections or 4 yield mode equations for nailed connections in single shear. The penetration depth factor was assumed to account for the other modes. The 2001 NDS eliminated the penetration depth factor, C_d, for nails, wood screws, and lag screws. The removal of this factor was coupled with the requirement to check all 6 yield limit equations per section 11.3.1. This change allows the effect of reduced penetration on strength to be calculated in a consistent manner with the yield mode equations. Nails in double shear are now calculated using the double shear equations in the 2001 NDS.
The 2001 NDS still has provisions for the minimum penetration permitted. For lag screws, this penetration limit is 4D excluding the tip. For nails and screws, this penetration limit is 6D including the tip, except in cases where 12d or smaller nails are used in double shear. When this exception occurs, the side member must be at least 3/8" thick and the nails must extend at least 3D beyond the side member and be clinched.
The 2001 NDS tabulated lag screw, wood screw, and nail values were calculated using penetrations of 8D, 10D, and 10D respectively. For users that rely on tabulated values for design rather than the calculation method, values for connections with reduced penetration can be conservatively calculated using the table footnotes. Note that main member thickness is assumed to be sufficient to provide full penetration of the fastener, except where noted in the table footnotes.
A connection calculator has been developed for the AWC website which provides a way to calculate design values for dowel-type connectors:
http://www.awc.org/calculators/connections/ccstyle.asp
The 2001 NDS still has provisions for the minimum penetration permitted. For lag screws, this penetration limit is 4D excluding the tip. For nails and screws, this penetration limit is 6D including the tip, except in cases where 12d or smaller nails are used in double shear. When this exception occurs, the side member must be at least 3/8" thick and the nails must extend at least 3D beyond the side member and be clinched.
The 2001 NDS tabulated lag screw, wood screw, and nail values were calculated using penetrations of 8D, 10D, and 10D respectively. For users that rely on tabulated values for design rather than the calculation method, values for connections with reduced penetration can be conservatively calculated using the table footnotes. Note that main member thickness is assumed to be sufficient to provide full penetration of the fastener, except where noted in the table footnotes.
A connection calculator has been developed for the AWC website which provides a way to calculate design values for dowel-type connectors:
http://www.awc.org/calculators/connections/ccstyle.asp
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