russed tower wind loads - epsilon 9ratio of solid to gross

huangyhg

trussed tower wind loads - epsilon (ratio of solid to gross
this is in regards to the calculation of cf (see fig. 6-22 in asce 7-02) for trussed towers using the following formula:
cf = 4.0e^2 - 5.9e + 4.0, where e is epsilon
max cf = 2.1 when e=1
~min cf = 3.94 when e=0.01
as epsilon (ratio of solid to gross area) increases, cf descreases.  according to this, as the element in question becomes more "solid", cf, and therefore the wind force f in eq. 6-25 decreases.  this seems counterintuitive to me, since the more "solid" something is, the more surface area it has for wind pressure to act upon.  what am i missing here?
as the tower becomes more solid, cf decreases, so your wind pressure decreases.  the area increases, however.  i would expect that the net effect would be that your wind force f increases.
fig 6-22 shows cf increasing for more solid round members but decreasing for more solid flat-sided members.  i'm not sure i understand this logic either.  try the wind loads and anchor bolt design for petrochemical facilities standard.  it seems to have a more reasonable approach.