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The third term of the 4-term equation is related to the slippage of nails fastening the sheathing to the top and bottom shear wall chords, i.e top and bottom wall plates.
Fastener Slip en - Wood Panels
The fastener slip en is taken from SDPWS Table C4.2.2D. Note that the slip is non-linear with respect to shear-per-fastener Vn .
Fastener Slip en - Gypsum Wallboard and Other Non-wood-panel
For gypsum wallboard, fiberboard, and lumber sheathing the value is taken from SDPWS Table C4.2.2D. Note that it does not depend on v at all for other materials, in fact is a constant, 0.76 mm = .03".
Fastener Load Vn
The load per fastener Vn is calculated by dividing the shear-per-unit-length v by the user-input panel edge spacing, yielding the force on each edge fastener.
Shear Value v on Either Side of Wall
Refer to Distribution to Sides of Composite Wall for an explanation of how shear is apportioned to each side of a composite wall.
Nails Greater than 10d
The 10d value is conservatively used for 16d nails, which may be selected for nail withdrawal strength for wind C&C loads.
Maximum Load per Fastener
The program does not limit the fastener shear to the maximum in Table C4.2.2D, or issue a failure warning in this case, as we determined that this level of loading always results in shear wall design failure for which a failure message is already output.
Specific Gravity Limitation
SDPWS Table C4.2.2D indicates that nail slip applies for lumber framing members with specific gravity of 0.5 or greater. As there is no guidance in SDPWS about what to do with materials such as S-P-F with specific gravity less than 0.5, analysis proceeds with the Table C4.2.2D values and a warning note appears under the Deflection table in the output