Towertalk
[Top] [All Lists]

## Re: [TowerTalk] "Wind Load" "Wind Area"

 To: towertalk@contesting.com, ersmar@comcast.net Re: [TowerTalk] "Wind Load" "Wind Area" K7LXC@aol.com Sat, 16 Dec 2006 11:05:22 EST
 ``` In a message dated 12/10/2006 7:11:24 A.M. Pacific Standard Time, towertalk-request@contesting.com writes: > The windload rating of a tower usually stipulates that the specified load is applied at some distance above the tower top, like maybe one or two f eet. If your multiple antenna installation spreads out your antennas over let's say 15 feet of mast (triband Yagi a foot above the tower, 2L 40M Yagi ten feet above that and a longboom VHF Yagi five feet above that), then you can't simply add the antennas' respective areas. You have to take into account the moment (leverage) that these various antennas at these various distances above the tower top impart to the tower. If you do this (spread out your antennas) you could very easily exceed the tower's maximum windload. > Another way of saying this is if your tower is rated at 20 sqft of load at one foot above the tower top, it is then rated for LESS than 20 sqft if that one antenna is MORE than a foot above the tower top. > There is an article by W7NI that was published in the NCJ for Sep/Oct 1982 and Mar/Apr 1983 and republished in Jan/Feb 1992 NCJ titled Antenna Mast Design. Stan goes over the fairly simple math involved in calculating the moment that is imparted on towers by antenna wind loads at various distances above the tower top. That was the article that got everyone aware of the increased windload bending moment with masts but unfortunately according to Dick Weber, PE, K5IU, his calculations and formulas were wrong. A much better and more accurate discussion of mast forces is in Dave Leeson's, ex-W6QHS, W6NL, book "Physical Design of Yagi Antennas". It's out of print but you can probably find a copy somewhere. It's got LOTS of interesting information about lots of tower and antenna system topics. Cheers, Steve K7LXC TOWER TECH _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
 Current Thread [TowerTalk] "Wind Load" "Wind Area", AD5VJ Bob Re: [TowerTalk] "Wind Load" "Wind Area", AD5VJ Bob Re: [TowerTalk] "Wind Load" "Wind Area", Pete Smith Re: [TowerTalk] "Wind Load" "Wind Area", Jim Lux Re: [TowerTalk] "Wind Load" "Wind Area", ersmar Re: [TowerTalk] "Wind Load" "Wind Area", Robert Chudek - KØRC Re: [TowerTalk] "Wind Load" "Wind Area", TexasRF Re: [TowerTalk] "Wind Load" "Wind Area", K7LXC <= Re: [TowerTalk] "Wind Load" "Wind Area", Todd Ruby