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[TowerTalk] SUMMERY Mast Lenght to Wind Load Question

 To: [TowerTalk] SUMMERY Mast Lenght to Wind Load Question RCARIELLO@si.rr.com (RCARIELLO) Sat Feb 8 07:25:50 2003
 ```Hello to all, A very hardy thanks to all that replied to my question. I have summarized some of the messages and included below. I hope this information will be as useful to others as is has been to me. Rich AA2MF ------------------------------------------ If you can get an answer from them, try the manufacturer. Years ago a Triex engineer told me at what point above the tower the allowed wind load went to zero (can't remember his name now). He said to do a linear derating from the top of the tower to zero. Sounds reasonable to me. 73 Don K5AQ --------------------------------------- Jim Lux IF you assume identical mast and identical connection to the top of the tower. AND If you assume that the wind speed is the same at both places (not necessarily valid.. average wind speed goes up with height, which is factored into "real" wind loading calculations) If the actual force due to wind remains the same, the bending force at the mast/tower attachment will be 15 times greater, because the same force is acting on a lever arm that is 15 times longer. Superficially, then, the limit would be 1 square foot (based on keeping the bending load the same). However, the mast's equivalent cross section will start to be a significant fraction of the total cross section (a 2" pipe 12 feet long has a 2 square foot cross section) The real question, in a practical situation, will be what's the strength limiting component? Is it the mast strength in flexure? Is it the load on the bearings? In this case how much of the mast sticks into the tower becomes quite important, although... if the moment is 15 times greater, the loads are 15 times greater, assuming the geometry doesn't change. -------------------------------------- The first thing you need to know is your county windspeed rating. You can look it up at www.championradio.com under Tech Notes. I offer a little program called MARC - the Mast, Antenna, and Rotator Calculator. you can get it at the aforementioned website for ten bucks. Steve K7LXC TOWER TECH CHAMPION RADIO PRODUCTS ===================================== ```
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