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Wind is an almost horizontal flow of air moving from an area of high pressure to an area of low pressure. [1] X Research Source Strong winds can cause great damage because it puts pressure on the surface of the structure. The magnitude of this pressure is called the wind load. The effect of wind depends on the size and shape of the structure. Wind load is a must-know parameter to design and build buildings with better safety and resistance to wind, and to install objects on the roof of buildings such as antennas.
Steps
Calculate the wind load using the general formula
- The formula for calculating the area depends on the surface shape. For flat walls, you use the formula Area = length x height. Calculate the approximate column surface area using the formula Area = diameter x height.
- In the SI system, you need to measure A in square meters (m 2 ).
- In the British system, you need to measure A in square feet (ft 2 ).
- This formula is taken from the American Society of Civil Engineers standards set. The factor 0.00256 is the result of a calculation based on typical values of air density and gravitational acceleration. [6] X Research Source
- Engineers use a more precise formula that considers factors such as the surrounding topography and type of building. You can find the calculation formula in the ASCE 7-05 series of standards, or use the UBC formula below.
- If you don’t know what the wind speed is, look up the highest wind speed in the area according to the Electronic Business Association (EIA) standards. For example, most of the United States is in Zone A with wind speeds of 38.7 m/s, but coastal areas are in Zone B (44.7 m/s) or Zone C (50 m/s).
- The standard drag coefficient for long cylinders is 1.2 and short cylinders is 0.8. These coefficients apply to antenna holders on many buildings.
- The standard drag coefficient for flat slabs such as building faces is 2.0 for long flat slabs, or 1.4 for short flat slabs.
- The drag coefficient has no units.
- Start by estimating the projected area. In this case, A=dw=(firstm)(0,02cm)=0,02m2{displaystyle A=dw=(1m)(0.02cm)=0.02m^{2}}
- Calculate wind pressure: P=0,613DRAW2=0,613(thirty first,32)=600WOMEN/m2{displaystyle P=0.613V^{2}=0.613(31.3^{2})=600N/m^{2}} .
- For short cylinders the drag coefficient is 0.8.
- Substitute into the equation: F=APOLDd=(0,02m2)(600WOMEN/m2)(0,8)=9,6WOMEN.{displaystyle F=APCd=(0.02m^{2})(600N/m^{2})(0.8)=9.6N.}
- 9.6 N is the wind load acting on the antenna.
Calculate the wind load using the E-Business Association’s formula
- A , P and Cd have the same meaning as in the generalized formula.
- Kz is the contact coefficient and is calculated from the height from the ground to the midpoint of the object. The unit of Kz is the meter.
- Gh is the recoil factor and is calculated over the entire height of the object. The unit of Gh is 1/m or m -1 .
- For flat walls, using the formula Area = length x width, measure the length and width of the wall where the wind is blowing.
- For cylinders or columns, you can approximate the area by length and width. In this case, the width is the cylinder or column diameter.
- For example, if the wind speed is 31.3 m/s, the wind pressure is 0.613 x 31.3 2 = 600 N/m 2 .
- Another way to calculate wind pressure at a particular velocity is to use standards for wind speeds in different geographical areas. For example, according to the Electronic Business Association (EIA), much of the United States is in Zone A with wind speeds of 38.7 m/s, but coastal areas are in Zone B (44.7 m/s). ) or Zone C (50 m/s).
- The standard drag coefficient for long cylinders is 1.2 and short ones is 0.8, commonly applied to antenna masts on many buildings.
- The standard drag coefficient for flat slabs such as building faces is 2.0 for long flat slabs, or 1.4 for short flat slabs.
- The difference between the drag coefficient of the flat plate and the cylinder is approximately 0.6.
- The drag coefficient has no units.
- For example, if you have an antenna 1 meter long and located 15 meters above the ground, z will be 14.5 meters.
- Kz = [z/33] (2/7) = [14.5/33] (2/7) = 0.8 m.
- For example, if you have an antenna 1 meter long and located 15 meters above the ground, Gh = 0.65+0.6/[(h/33) (1/7) ] = 0.65+0, 6/[(16/33) (1/7) ] = 1.32 m -1
- Let’s say you want to calculate the wind load acting on an antenna with a length of 1 meter and a diameter of 2 cm, with a wind speed of 31.3 m/s. The antenna is placed on the roof of a 15m high building.
- Start by calculating the projected area. In this case, A = lxw = 1 mx 0.02 m = 0.02 m 2 .
- Calculate wind pressure: P = 0.613 x V 2 = 0.613 x 31.3 2 = 600 N/m 2 .
- For short cylinders the drag coefficient is 0.8.
- Calculate the coefficient of contact: Kz = [z/33] (2/7) = [14.5/33] (2/7) = 0.8 m.
- Calculate the wind recoil coefficient: Gh = 0.65+0.60/[(h/33) (1/7) ] = 0.65+0.60/[(16/33) (1/7) ] = 1.32 m -1
- Substitute into the equation: F = A x P x Cd x Kz x Gh = 0.02 x 600 x 0.8 x 0.8 x 1.32 = 10 N.
- 10 N is the wind load acting on the antenna.
Calculate the wind load using the formula of the UBC-97 standard (Uniform Building Code)
- Wind pressure (N/m 2 ) is calculated according to the formula P= Ce x Cq x Qs x Iw , where Ce is the combined coefficient of the height, exposure and recoil of the wind, Cq is the pressure coefficient force (equivalent to the drag coefficient in the two equations above), Qs is the stagnation pressure of the wind, and lw is the important factor. All these values can be calculated or looked up from the respective tables.
- For flat walls, using the formula Area = length x width, measure the length and width of the wall where the wind is blowing.
- For cylinders or columns, you can approximate the area by length and width. In this case, the width is the cylinder or column diameter.
- “Exposure type B is terrain with buildings, trees or other unevenness, covering at least 20% of the surrounding area and extending for 1.6 km or more from the considered location.”
- “Contact type C is flat and generally open terrain, extending 0.8 km or more from the site of consideration.”
- “Exposure type D is the most severely impacted terrain, with an average wind speed of 129 km/h or higher, and a flat, unobstructed terrain, surrounded by open water.”
- The standard drag coefficient for long cylinders is 1.2 and short ones is 0.8, commonly applied to antenna masts on many buildings.
- The standard drag coefficient for flat slabs such as building faces is 2.0 for long flat slabs, or 1.4 for short flat slabs.
- The difference between the drag coefficient of the flat plate and the cylinder is approximately 0.6.
- The drag coefficient has no units.
- For example, if the wind speed is 31 m/s, the stagnation pressure of the wind is 0.613 x V 2 = 0.613 x 31.3 2 = 600 N/m 2 .
- Another way is to use standards for wind speeds in different geographical areas. For example, according to the Electronic Business Association (EIA), much of the United States is in Zone A with wind speeds of 38.7 m/s, but coastal areas are in Zone B (44.7 m/s). ) or Zone C (50 m/s).
- Calculations for a standard use building will have an important factor of 1.
- Let’s say you want to calculate the wind load acting on an antenna with a length of 1 meter and a diameter of 2 cm, with a wind speed of 31 m/s. The antenna is located on the roof of a 15 m high building in an area with Exposed Type B terrain.
- Start by calculating the projected area. In this case, A = lxw = 1 mx 0.02 m = 0.02 m 2 .
- Determine Ce . According to table 16-G, using the height of 15 m and the terrain of Contact Type B, we can find Ce is 0.84.
- For short cylinders the drag coefficient or Cq is 0.8.
- Calculate Qs : Qs = 0.613 x V 2 = 0.613 x 31.3 2 = 600 N/m 2 .
- Determine the critical factor. This is a standard building so lw = 1.
- Substitute into the equation: F = A x P = A x Ce x Cq x Qs x Iw = 0.02 x 0.84 x 0.8 x 600 x 1= 8 N.
- 8 N is the wind load acting on the antenna.
Advice
- You should know how wind speed varies at different heights from the ground. The wind speed increases with the height of the structure and the closer it is to the ground, the more erratic it is, because it is affected by structures on the ground.
- It should be remembered that it is this erratic variation that will reduce the accuracy of the wind load calculations.
wikiHow is a “wiki” site, which means that many of the articles here are written by multiple authors. To create this article, 14 people, some of whom are anonymous, have edited and improved the article over time.
This article has been viewed 28,608 times.
Wind is an almost horizontal flow of air moving from an area of high pressure to an area of low pressure. [1] X Research Source Strong winds can cause great damage because it puts pressure on the surface of the structure. The magnitude of this pressure is called the wind load. The effect of wind depends on the size and shape of the structure. Wind load is a must-know parameter in order to design and construct buildings with better safety and resistance to the wind, and to install objects on the roof of buildings such as antennas.
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