Wind Loads on a flagpole??

[civilgee]

I do not see any reference to this in either AASHTO LTS-4, 2001 or ASCE-7, 98. Given F=0.00256*Kz*Kh*I*Cd*(V)^2*A, what would you use for the Cd? All other coefficients are easy to calculate. Is this the correct methodology?

 

[JedClampett]

See ANSI/NAAMM FP1001-97 Guide Specifications for Metal Flagpoles.

 

[dbuzz]

Australian Standard AS 1170.2:2002 Structural design actions: Wind actions, Appendix F, has a treatment for calculating the aerodynamic shape factor for free flags, which includes the dynamic effects from flutter.

C = 0.05 + [0.7 * m/(p*c) * (A/c^2)^-1.25]

Where:
- m is the unit mass of the flag (kg/m^2)
- q is the density of air (nominally 1.2 kg/m^3)
- c is the height of the flag (m) {Note this is not height above ground of flag but actual height of flag}
- A is the area of flag perpendicular to wind direction (m^2)

 

[J1D]

dbuzz,
Is A just the flag area? With the wind blow, the flag will be in the wind direction and vibrate.

 

[btrueblood]

civilgee,

Cd is the drag coefficient for a cylinder; roughly 1.0 max for high wind speeds (> 100 mph), assuming a 6" diameter; and it won't change much at higher speeds or at diameters within .5x to 2x of that. Most good fluid dynamics textbooks will give a plot of the Cd of a cylinder for various Reynold's numbers.

 

[civilgee]

I appreciate the help. I will order the NAAMM FP 1001-97 standard and see if that helps. As far as the wind load on the pole I have that under control....it is just how to determine the loads from a flag that is flapping. Thanks again.

 

[jheidt2543]

This may be an oversimplification, but why not call a flag manufacturer, give them the size of the flag and pole and where it is to be located and have them provide the foundation loads?

 

[blake989]

If you are accustomed to the ASCE 7 code, chances are this would be classified as a flexible structure with a frequency less than 1Hz. It is also a round pole. If you follow the code closely, there are specific methods for calculating the wind pressure for these types of structures. Reference ASCE 7-95 for some background information first.