Dear Kamali,
The horizontal shear force is distributed among all the legs based on their moment of inertia about an axis perpendicular to the direction of the wind (or Seismic). In the default method we find maximum inertia of one leg and then use it to find the maximum shear acting on any one leg.
I have added some more clarification in the printout recently. This should be available in the next build of PV Elite.
There is also another method that can be activated from the leg dialog "Employ Directional Check for W and C types". This method varies the angle of attack of the wind or seismic and tried to find the worst one. But, it only works for I-beams, Channels and Tubing. You can also try it out if you have one of these led shapes.
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Best Regards,
Mandeep Singh
CADWorx & Analysis Solutions
Hexagon PPM