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.

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