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The three-term deflection combines the shear and nail slip terms
with
where Ga is published in the SDPWS shear capacity Tables 4.3A and 4.3B for seismic design only. The formula for Ga for seismic design is given ins C4.2.2-3 as
Where vs is the shear wall capacity for seismic design. Shearwalls calculates Ga using the formula. In most case, the value of Ga is the same as that listed in Table 4.2B, but it may be slightly different because the use of the equation allows us to consider the number of plywood plies when evaluating Gvtv, whereas note 3 of Table 4.2B approximates this effect by applying a factor of 1.2.
Wind Deflections
The factor 1.4 appearing in the formula for Ga converts ASD-level shear wall design forces to strength-level deflections (refer to Shear v, Height h, and Length b for details ). For main wind force resisting system deflections that are used to distribute forces in shear line, ASD-level forces are used, so the 1.4 factor is unnecessary. The formula for Ga is just
For wood structural panels and fiberboard, this results in the same Ga values as for seismic design because the shear wall capacity vw = 1.4 vs. It is important to note that this is merely a coincidence; the difference in capacity for wind vs. seismic is for unrelated reasons pertaining to a historical increase in design wind loads related to test strengths. The increase was not applied to other materials such as gypsum wallboard, and these have different Ga values for wind vs. seismic design.