[TowerTalk] Do Bracketed Towers Have an Overturning Moment?

[Roger (K8RI)]

Gene Smar wrote:
> Jeff:
>
>      In a self-supporting tower, all the overturning moment is applied at the concrete base.  For my short (64-foot) tower and its modest HF Yagi load I constructed a base of 10.5 cuyd of 3500 PSI concrete with rebar, per Trylon specs.
>
>      For a house-bracketed tower, this overturning moment is applied to the bracket, its mounting hardware and the house structure.  (Because the rigid fastening (bracket) is higher above ground than a SS tower, this force would be lower than on a SS tower.) You can see why using a couple of half-inch lag bolts into the siding and wood sheathing of a typical residential installation may not generate enough holding force to keep from pulling out in high winds.  That's why using a house bracket requires a bit more engineering than we have been discussing here on TT.  
>
>   
And why the wood walls of many homes are not sufficient without 
modification to hold a tower bracket.
OTOH at one time ROHN made a dirt base and I believe they still make the 
drive rods. If the soil is of the proper quality I'd have not problem 
using a dirt base under a 30' bracketed 25G holding a couple of UHF and 
VHF antennas or even a small tribander.
>      For more info on the subject of house brackets for towers check out the 8/96 QST article by K1KP.  Good luck with your study/project.
>
>   
73

Roger (K8RI)