[TowerTalk] Rohn 45G/55G bracketed towers

[K7LXC]

In a message dated 98-03-08 20:04:07 EST, ginsburg@BayNetworks.COM writes:

> I'm interested in hearing from anyone out there who has had a Rohn 45G
>  or 55G bracketed tower design done for them by a PE or Mechanical
>  Engineer. In particular, I'd like to know how high above a single
>  house bracket I can go without extra support, given an antenna of 8
>  sq. ft. windload. If I'm reading the Rohn catalog right, it looks like
>  55G can handle 10 sq ft at about 30' above the bracket, 80 MPH no ice.

     The Rohn pamphlet "Manufacturer's Technical Information for Bracketed or
Self Supporting Towers" has free-standing and housebracketed specs for 25, 45,
55G and SSV. It's free for an SASE to TOWER TECH, Box 572, Woodinville, WA,
98072. 

     The specs cited above are for a tower height of 100 feet with
housebrackets at 66 and 33 feet. For a 50 foot tower (brackets at 36' and
18'), 55G is rated for 51.7 square feet. 

     Also, 55G will free-stand at 40 feet with 8.0 sq.ft. of capacity at 80
MPH. Obviously, using any kind of additional bracing will increase the
capacity and reliability significantly. 

    If you're in Essex County, MASS, you're in a 90 MPH wind speed zone plus
being within 100 miles of hurricane oceanline so I'd recommend over-
engineering the whole installation.
>  
>  I read the article in Aug. 96 QST by K1KP and N1CQ that describes an
>  interior support system for the bracket. Unfortunately I don't have an
>  attic so this isn't an option. Am I out of luck without the ability to
>  provide interior support? Is it impossible even with 45G or 55G to
>  have 20 or 30' of tower above a single bracket which is just secured
>  to house studs?

      I wouldn't do it. You need to anchor the housebracket to a wall plate -
either the wooden kind on top of your stud wall or one installed on the other
side of the wall. The hardware and studs will probably rip right out in the
event of a big one.      
>  
>  Before seriously pursuing a bracketed design I would definitely hire a
>  PE. I'm just looking for a sanity check on whether or not what I'm
>  inquiring about is feasible.
>  
      Go to the ARRL web page and look under VCE's (Volunteer Civil Engineers)
to get a professional opinion in your area. Or hire the PE. Anything's
possible but you need professional advice and guidance. 

     A TowerTalkian in Utah had an aggressive antenna system on 45G
housebracketed to his brick wall. From the photos, I think the bolts or screws
were just in lead anchors. There was no backing plate or reinforced anchor ala
K1KP. The hardware let loose in a microburst and fortunately the whole thing
fell across the fence without any injuries or damage to anyone's house. Other
than about a $15K insurance claim and a lot of work to get it rebuilt, it
could have been worse. 

73,  Steve  K7LXC

      TOWER TECH --- professional tower supplies and services for amateurs

--
FAQ on WWW:               http://www.contesting.com/towertalkfaq.html
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com
Search:                   http://www.contesting.com/km9p/search