Hi, PvElite implements procedure 4-11 by Moss.
For horizontal loads in longitudinal direction, outside and inside ribs are verified by determining a unit force per length "fu", and then using this unit force to check Outside and Inside ribs as if they where beams.

Now, Moss and consequently PvElite define fu as reported in attached image.

I wonder, why defining fu=FL / 2*A ?
Wouldn't it be correct to use FL / A ?

It seems that Moss and PvElite use half the required force per unit length to do the calculation...