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The setting Always use DF plywood specific gravity for nail embedment strength f1 in O86 12.9.3 , as permitted by 11.6.2.2 allows you to decide whether to take advantage of the non-mandatory equation for plywood or OSB sheathing embedment strength from O86 11.6.2.2.(a)
f1 = 51 (1 - 0.1dF)
rather than the equation for connection design in O66 12.9.3.2
f1 = 104 G (1 - 0.1dF),
Since G is the mean relative density (specific gravity) = 0.49 for Douglas-fir plywood (DFP) and 0.42 for Canadian Softwood plywood (CSP), effectively this means to use DFP strength for CSP plywood and OSB sheathing panels.
f1 is used in the calculation of unit lateral nail strength Nu, which is used in the calculation in 11.6.2.2.(a) of the shear resistance Vrs when governed by fastener strength.
In the Detailed Shear Wall Design output, the words (DF plywood) appear after the value for G if this setting has been selected.
This setting is available only if CSA O86-19 is selected as the design code.