I know this isn't the answer you are looking for, how much force does it take to buckle sheet steel? Not much, it would depend on gauge, fastening schedule, scheme and the specfic product. Call a supplier's tech rep. Ask youself what does failure look like, how rapid and how well can you predict and avert failure during a storm? Lumber truss roof pole barns require bracing across the webbing and so should other forms.
