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The rolling shear resistance Vs is checked:
Vs’ = CD Ct Vs
where the values of Vs are those listed in table A-2 of the PRG. For custom CLT layups, and for fire design, Vs is adapted from O86 8.4.4.2
Vs = 2/3 A Fs
A is the gross cross-sectional area for loading on the major axis, and for the minor axis it is the cross-sectional area minus the area of the outermost layers.
Fs is the rolling shear resistance, which is assumed to be the same for longitudinal and transverse laminations. If you have a custom CLT material with differing Fs for transverse vs. longitudinal layers, it is recommended to use the lower Fs as the material rolling shear resistance.
This method conservatively assumes that the maximum shear in the member cross section occurs in a transverse layer, where rolling shear governs, as rolling shear strength Fs is typically much lower than shear strength Fv. For custom CLT materials with higher Fs than Fv, it is recommended to enter the Fv value in the database as Fs.
Fire Design
The program applies an adjustment factor of 2.75 to the rolling shear strength Fs, from AWC Technical Report 10, Table 1.4.2, as it is not listed in NDS Table 16.2.2.
The calculation of the gross cross-sectional area does not include final partially charred layer if is transverse to the axis of loading.
For the unusual case of design in the transverse direction with double outermost layers, both layers at the top and the bottom of the panel are omitted from the calculation of A.