Towertalk
[Top] [All Lists]

## Re: [TowerTalk] Aluminum mast

 To: kc8hz@hotmail.com, towertalk@contesting.com Re: [TowerTalk] Aluminum mast Telegrapher9@aol.com Thu, 4 Jan 2007 10:50:00 EST
 ```Roger, here's a link to some good information on tower stresses: http://www.heightstowers.com/tower_specs_and_tutor.htm http://www.google.com/search?q=antenna+element+bending+moment+formula&hl=en&lr =&ie=ISO-8859-1 The "I" value for a circular pipe is I= Pi (Do^4-Di^4)/(64) where Do=outer diameter of pipe Di= inner diameter of pipe For your 2.000", 0.25" wall pipe this gives I = 0.54 The yield strength of 6061-T6 is 35,000 PSI. The bending moment when the mast will yield is 0.54(35,000) = 19,000 PSI Let's say you have an antenna with a 6 sq. ft. wind area at the top of the 20 ft. mast. The wind is gusting to 80 mph. The force per sq. foot is about 16 lb. There are more accurate numbers then the 9 lb/sq ft I use at 60 mph. This is conservative and is from an old ARRL antenna handbook. For 80 mph the force per sq foot is (80/60)^0.5 X 9 lb. The wind force on the antenna is 96 lb. The bending moment at the base of the mast is (96lb)(20') = 1920 lb-ft. Muliply by 12 to get PSI, (1920 lb-ft)(12 in/ft) = 23,000 PSI (is this correct?). This mast will fail. It can stand a gust to 72 mph. The highest recorded wind velocity for your area can be found by a google search. This must be adjusted for antenna height and the terrain. The links above contain some information on this. Physical Design of Yagi's has all of this. I can't find my copy right now. Before using the formula's I have put down here one should (must) double check using a good written source. I could be in error. There is also icing to take into consideration in some areas of the world. Altogether this mast thing is just an engineering calculation. When performed with worst case numbers you can be sure that your antennas will stay in the air. Dave WX7G http://72.14.253.104/search?q=cache:fJ4kX54h3aAJ:www.arraysolutions.com/images/KT9OMpartI.pdf+antenna+mast+bending+moment+formula&hl=en&gl=us&ct=clnk&cd=3&; ie=UTF-8 _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
 Current Thread [TowerTalk] Aluminum mast, Roger Kissel Re: [TowerTalk] Aluminum mast, D. Scott MacKenzie Re: [TowerTalk] Aluminum mast, Bob Maser Re: [TowerTalk] Aluminum mast, Dave NØRQ [TowerTalk] RE : Aluminum mast, hermans Re: [TowerTalk] Aluminum mast, Clint Talmadge Re: [TowerTalk] Aluminum mast, Telegrapher9 Re: [TowerTalk] Aluminum mast, Telegrapher9 Re: [TowerTalk] Aluminum mast, Dave NØRQ Re: [TowerTalk] Aluminum mast, Telegrapher9 <= Re: [TowerTalk] Aluminum mast, K7LXC