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The slenderness ratio CB in 7.5.6.4.3 is used to compute the lateral stability factor KL in 7.5.6.4.4, and itself is limited to being less than 50 . If this value is exceeded, a message appears on the screen and moment design is not calculated, showing instead a failure for slenderness ratio.
Multi-ply members:
For multi-ply members, the CSA O86 (6.5.3.2.4 and 7.5.6.3.3) indicates that the full member width may be used to calculate the depth-to-width ratio in 7.5.6.3.1 provided the individual members are fastened together securely at intervals not exceeding 4 times the depth, however it does not provide guidance on whether the full member width can be used to calculate the slenderness ratio in 7.5.6.4.3.
Unpublished research has shown that nailed and bolted beams have at most 30% composite action effect in terms of resisting torsional buckling, so there is an option in the Design Settings to allow either the full member width or the individual ply width for slenderness calculations. It is recommended to use singly ply width unless there is certainty that the individual members are fastened together such that they act as a unit