EVALUATING LOADS DUE TO ANTENNAS ON TOWERS
Every communication tower has a large number of different types of antennas , panel/dish, at various heights and different azimuth angles. Objective of the article is to convert all antenna loads to a single “equivalent wind obstruction area” at top of the tower for that particular case.
Having done that , it will become possible to compare various antenna installations for loading and to determine available structural capacity of existing communication towers to take up more antennas.
Load generated by any antenna on tower depends on following factors
a) Height of installation More the height, more the load
b) Relative angle between direction of wind and face of antenna
If antenna is presenting its face to wing then the drag coefficient is expected to be more
than in other cases.
c) Physical geometry of antenna - A dish facing wind will generate more resistance compared to flat surface or a round rod. A dish with radome will put less wind load s compared to dish without radome on tower. A 3 m dia dish will generate more wind resistance as compared to a 1 meter dia dish.
If 4 similar antennas are mounted in different directions on a tower and wind is blowing in one direction , then all 4 antennas will present different angles to the wind.
This means that each of these 4 antennas will exert different loads on tower.
The direction of wind also will keep on changing with time.
Which means that it is necessary that load on tower should be calculated with different wind directions for a particular set of antennas on tower.
The worst load should be taken out of all these wind directions. This worst load be converted into a “ single equivalent wind obstruction Area “: at top of tower.
Elaborate software has been developed by POLYQUAL based on drag coefficients provided for different angles by International standards to calculate the equivalent wind obstruction area.
You are welcome to fill , data for 3 antennas in appended form “equivalent wind obstruction area “ below, Click on Submit button and result will be displayed on "Display Sheet" below the form after processing time of 3 minutes approx