[TowerTalk] "Wind Load" "Wind Area"

[ersmar at comcast.net]

Bob:

     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 feet.  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.  


73 de
Gene Smar  AD3F


 -------------- Original message ----------------------
From: "AD5VJ  Bob" <rtnmi at sbcglobal.net>
> Also for total WINDLOAD with multiple antennas, do I determine each individual 
> antennas WINDLOAD and then simply add them all
> together to know if a structure will support them all based on its rated 
> WINDLOAD?
> 
>   73 fer nw es gud DX,
> QSL VIA: BUR, LotW, e-QSL
> Bob AD5VJ(AAR6VM)
> Old calls: WY5L/KH3-KE5CTY-N5IET
> http://www.ad5vj.com/
> 
> Member: CTDXCC, NTCC, STXDXCC
> FISTS: # 12637, SKCC# 2369
> 10X# 37210, FP#-1141
> SMIRK#-5177, RARS #-149
> 
>  
> 
>  
> 
> > -----Original Message-----
> > From: towertalk-bounces at contesting.com 
> > [mailto:towertalk-bounces at contesting.com] On Behalf Of AD5VJ Bob
> > Sent: Saturday, December 09, 2006 11:00 PM
> > To: towertalk at contesting.com
> > Subject: [TowerTalk] "Wind Load" "Wind Area"
> > 
> > In searching around learning abt WINDLOAD, I have found two 
> > terms that seem to be the same:
> > 
> > "Wind Load" "Wind Area"
> > 
> > Are these one and the same?
> > 
> >   73 fer nw es gud DX,
> > QSL VIA: BUR, LotW, e-QSL
> > Bob AD5VJ(AAR6VM)
> > Old calls: WY5L/KH3-KE5CTY-N5IET
> > http://www.ad5vj.com/
> > 
> > Member: CTDXCC, NTCC, STXDXCC
> > FISTS: # 12637, SKCC# 2369
> > 10X# 37210, FP#-1141
> > SMIRK#-5177, RARS #-149
> > 
> >  
> > 
> > 
> > 
> > _______________________________________________
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