I'm not sure if they are ineffective at all. If I were going to model them, I'd check deflections using Roark or other reference for a plate fixed end supported on two adjacent sides with one that was cantilevered.
I'd then calculate the equivalent stiffness plate thickness that would give the two side supported model the same deflection. I'd use that reduced thickness for my prying action thickness to calculate tension. Alternatively, use the cantilevered thickness with the two side supported model to determine the reduced prying action force.
As I noted, "I suspect the prying action will be reduced substantially." That's the reason I sent on the query.
As far as double Q forces, I just checked my SMath program of 21/11/26, and both forces are included.
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So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates
-Dik