open structure wind force on diagonal direction

huangyhg

open structure wind force on diagonal direction
asce figure 6-23 has cf factor calculation for open trussed tower. does anybody know how to calculate the wind force if the wind blows from other direction? say, digonal direction.
asce says to use 75% wind force simultaneously on both orthogonal directions. that's true for enclosed building. but if i follow the figure 6-23, i will get a much higher result. here is the calc.:
say, i have a 4 column square tower. i assign wind force on the windward 2 columns according to the figure. if i look at the diagonal direction, there are 3 columns exposed to the wind direction. that's means all the 3 columns must be assigned.
i wonder is there any guideline for calculating the diagonal wind force on open structure.
thank you
footnote 4 of figure 6-23 of 7-05 seems pretty clear: use the direction producing maximum   
my question was: how to calculate the diagonal wind force on open structure?  
in an open-trussed tower with four legs, i fail to see how any fewer than four legs would be exposed to the wind, regardless of the direction.  load all four and check overturning in the orthoginal and diagonal directions.
mike mccann
mmc engineering
but the "guideline for wind load of asce" says you only need to apply to the front face of the truss tower.only 2 columns needs to be assigned.
ok.  i'm looking at figutre 6-23, note 1 where it says that ... "... the area af ... shall be the solid area of a tower face projected on the plane of that face for the tower segment under consideration." (caps added for emphasis)
to me, this implies that if you are considering all four legs of the tower, the structure as a whole, then all the members of both the front and rear faces of the tower need to be considered for normal wind forces.  
correspondingly, if you are looking at in diagonal direction, then the projected area of all four sides needs to be considered, but the resultant wind force multiplied by 0.707 to account for the diagonal inclination of the sides of the structure - a wind shedding effect as it were.   
mike mccann
mmc engineering