Drag Coefficient 2

[sfinlayson]

Does anyone know what the drag coefficient is for an aluminum flag pole? I am trying to do an analysis with a 90 mph wind speed.

 

[LOKSTR]

sfinlayson,

If you have access to "EIA/TIA-222-F or G" Standard, there are tables for drag coeff. for round and octagonal monopoles.
In Canada, S37-01 is followed instead of EIA/TIA standard and also has the same tables.

In NBCC-95 Commentary Fig. B-18 can be used to get the wind pressure without going thru calculation of drag coeff.

Hope this helps.

Lokstr

 

[sfinlayson]

Thanks. I don't have access to that standard. I know it is located in AASHTO Standard Specifications of Highway Signs, Luminaires, and Traffic Signals, but I don't have access to that manual either.

 

[Lion06]

If you have access to AASHTO for design of luminaires, I am pretty certain you will find it in there. I don't think it is specific to aluminum, but you really just need it for a round pole, correct?
It is in Section 3.8.6 in the 2001 AASHTO code for signs, luminaires, and something else. They give equations for different shapes, but I didn't see anything about materials. I don't think it will matter, though.

 

[LOKSTR]

You can use a coeff. of 1.2 for drag for your pole. It doesn't matter what material it is made up of.

 

[dbuzz]

Don't forget the load induced by wind on the flag. This is how the Australian standard for wind loads, AS 1170.2, calculates the aerodynamic shape factor for free flags, including dynamic effects from flutter:

C_fig = 0.05 + 0.7 * [m_f / ([ρ]_air*c)] * (A_ref / c²)^-1.25

where
C_fig = aerodynamic shape factor (dimensionless)
m_f = unit mass of flag (kilograms per square metre)
[ρ]_air = density of air (1.2 kilograms per cubic metre)
c = height of flag (metres)
l_f = length of flag (metres)
A_ref = area of flag (square metres)
for a rectangular flag, A_ref = c * l_f
for a pennant flag, A_ref = 0.5 * c * l_f

The design wind pressure is then:

p = 0.5 * [ρ]_air * V_des² * C_fig

where:
p = design wind pressure (pascals, 1 Pa [≅] 0.02 psf)
[ρ]_air = density of air (1.2 kilograms per cubic metre)
V_des = design wind speed (metres per second)
C_fig = aerodynamic shape factor (dimensionless)

 

[dbuzz]

Further to my post yesterday, note that the aerodynamic shape factor, C_fig, has a maximum value of 0.76.

 

[oldrunner]

Buy the ANSI/NAAMM FP1001 "Guide Specifications for Design of Metal Flagpoles" It has a sample calculation of an aluminum pole.

https://www.naamm.org/items.aspx

It's $25 and you also get another manual. You will need to know the size of the flag and what's it is made of.