The formula to calculate area depends on the shape of the face. For a flat wall, use the formula Area = length x height. Approximate the area of a column face with Area = diameter x height. For SI calculations, measure A in square meters (m2). For imperial calculations, measure A in square feet (ft2).
This formula is based on the American Society of Civil Engineers code. The 0. 00256 coefficient is the result of a calculation based on typical values for air density and gravitational acceleration. [6] X Research source Engineers use a more accurate formula to take into account factor such as the surrounding terrain and type of construction. You can look up one formula in ASCE code 7-05, or use the UBC formula below. If you’re not sure what the wind speed is, look up the peak wind speed in your area using the Electronic Industries Alliance (EIA) standard. For example, most of the U. S. is in Zone A with 86. 6 mph wind, but coastal areas might lie in Zone B (100 mph) or Zone C (111. 8 mph).
The standard drag coefficient for a long cylinder tube is 1. 2 and for a short cylinder is 0. 8. These apply to antenna tubes found on many buildings. The standard coefficient for a flat plate such as the face of a building is 2. 0 for a long flat plate or 1. 4 for a shorter flat plate. The drag coefficient has no units.
Start by estimating the projected area. In this case, A=dw=(3ft)(0. 5in)(1ft/12in)=0. 125ft2{\displaystyle A=dw=(3ft)(0. 5in)(1ft/12in)=0. 125ft^{2}} Calculate the wind pressure: P=0. 00256V2=0. 00256(702)=12. 5psf{\displaystyle P=0. 00256V^{2}=0. 00256(70^{2})=12. 5psf}. For a short cylinder the coefficient of drag is 0. 8. Plugging into the equation: F=APCd=(0. 125ft2)(12. 5psf)(0. 8)=1. 25lbs. {\displaystyle F=APCd=(0. 125ft^{2})(12. 5psf)(0. 8)=1. 25lbs. } 1. 25 lbs is the amount of wind load on the antenna.
A, P, and Cd are the same variables used in the generic equation. Kz is the exposure coefficient and it is calculated by taking into account the height from the ground to the midpoint of the object. The units of Kz are feet. Gh is the gust response factor and it is calculated by taking into account the entire height of the object. The units of Gh are 1/feet or ft-1.
For a flat wall, use the formula Area = length x width, measuring the length and width of the wall where the wind is hitting it. For a tube or column, you can also approximate the area using length and width. In this case, the width will be the diameter of the tube or column.
For example, if the wind speed is 70 mph, the wind pressure is 0. 00256 x 702 = 12. 5 psf. An alternative to calculating wind pressure at a particular wind speed is to use the standard for various wind zones. For example, according to the Electronic Industries Alliance (EIA) most of the U. S. is in Zone A with 86. 6 mph wind, but coastal areas might lie in Zone B (100 mph) or Zone C (111. 8 mph).
The standard drag coefficient for a long cylinder tube is 1. 2 and for a short cylinder is . 8 These apply to antenna tubes found on many buildings. The standard coefficient for a flat plate such as the face of a building is 2. 0 for a long flat plate or 1. 4 for a shorter flat plate. The difference between drag coefficients for flat and cylinder items is approximately 0. 6. The drag coefficient has no units.
For example, if you have an antenna that is 3 ft long and 48 ft off the ground, z would be equal to 46. 5 ft. Kz = z/33 = 46. 5/33 = 1. 1 ft.
For example, if you have an antenna that is 3 ft long and 48 ft off the ground, Gh = . 65+. 60/[(h/33)(1/7)] = . 65+. 60/(51/33)(1/7) = 1. 22 ft-1
For example, let’s say you want to determine the wind load on an antenna that is 3 feet long with a diameter of 0. 5 inches in a gust of 70mph winds. It is placed on top of a 48 ft high building. Start by calculating the projected area. In this case, A = l x w = 3 ft x (0. 5in x (1 ft/12 in)) = 0. 125 ft2. Calculate the wind pressure: P = 0. 00256 x V2 = 0. 00256 x 702 = 12. 5 psf. For a short cylinder the coefficient of drag is 0. 8. Calculate the exposure coefficient: Kz = z/33 = 46. 5/33 = 1. 1 ft. Calculate the gust response factor: Gh = . 65+. 60/[(h/33)(1/7)] = . 65+. 60/(51/33)(1/7) = 1. 22 ft-1 Plugging into the equation: F = A x P x Cd x Kz x Gh = 0. 125 x 12. 5 x 0. 8 x 1. 1 x 1. 22 = 1. 68 lbs. 1. 68 lbs is the amount of wind load on the antenna.
Wind pressure (PSF) is calculated as P= Ce x Cq x Qs x Iw, where Ce is the combined height, exposure and gust response factor, Cq is a pressure coefficient (it is equivalent to the drag coefficient in the previous two equations), Qs is wind stagnation pressure, and Iw is importance factor. All of these values can be calculated or obtained from the appropriate tables.
For a flat wall, use the formula Area = length x width, measuring the length and width of the wall where the wind is hitting it. For a tube or column, you can also approximate the area using length and width. In this case, the width will be the diameter of the tube or column.
“Exposure B is terrain with buildings, trees or other surface irregularities covering at least 20 percent of the surrounding area and extending 1. 6 kilometers or more from the site. ” “Exposure C has terrain that is flat and generally open, extending 0. 8 km or more from the site. ” “Exposure D is the most severe, with basic wind speeds of 129 km/hr or greater and terrain that is flat and unobstructed facing large bodies of water. ”
The standard drag coefficient for a long cylinder tube is 1. 2 and for a short cylinder is . 8 These apply to antenna tubes found on many buildings. The standard coefficient for a flat plate such as the face of a building is 2. 0 for a long flat plate or 1. 4 for a shorter flat plate. The difference between drag coefficients for flat and cylinder items is approximately 0. 6. The drag coefficient has no units.
For example, if the wind speed is 70 mph, the wind stagnation pressure is 0. 00256 x 702 = 12. 5 psf. An alternative to this calculation is to use the standards set for various wind zones. For example, according to the Electronic Industries Alliance (EIA) most of the U. S. is in Zone A with 86. 6 mph wind, but coastal areas might lie in Zone B (100 mph) or Zone C (111. 8 mph).
Calculations for buildings with standard use have an importance factor of one.
For example, let’s say you want to determine the wind load on an antenna that is 3 feet long with a diameter of 0. 5 inches in a gust of 70mph winds. It is placed on top of a 48 ft high standard building in an area with an exposure B terrain. Start by calculating the projected area. In this case, A = l x w = 3 ft x (0. 5in x (1 ft/12 in)) = 0. 125 ft2. Determine Ce. Based on table 16-G, using the height of 48 ft and exposure B terrain, Ce is 0. 84. For a short cylinder the coefficient of drag or Cq is 0. 8. Calculate Qs: Qs = 0. 00256 x V2 = 0. 00256 x 702 = 12. 5 psf. Determine importance factor. This is a standard building therefore, Iw is 1. Plugging into the equation: F = A x P = A x Ce x Cq x Qs x Iw = 0. 125 x 0. 84 x 0. 8 x 12. 5 x 1= 1. 05 lbs. 1. 05 lbs is the amount of wind load on the antenna.
