asce 7-05 open buildings - case a b

huangyhg

asce 7-05 open buildings - case a & b
i have searched through the code and cannot find anything to explain exactly what case a and b are for open buildings for pitched free roofs. any help??
the two load cases are used to encompass the worst case load combinations on free-standing canopies.
lc a - worst case uplift (or downard)
lc b - worst case moment (due to differential pressures)
bascially, for cantilevered canopies, like gas station canopies, only putting large uplift forces on the surface is only half the game.  most canopy failures occur due to the moment (look at pictures from andrew, hugo, etc.) from differential wind pressures.