Re: [TowerTalk] Roof Mounted Self Supporting Tower...

[Jim Lux <jimlux@earthlink.net>]

At 10:02 AM 11/12/2003 -0800, Dino Darling wrote:
> Hello Comrades!
>
> I doing some leg work for the possibility of placing a 40' self supporting 
> tower on the flat roof of a gym for a communications station/disaster 
> shelter.  The tower will most likely hold the M2 Log Periodic and a 
> substantial vertical for VHF/UHF.  Also, a 80 meter dipole.  I picked 40' 
> because the roof is 20'+ and I want to be at least 60' off the ground.
>
> I am doing my homework to look at different towers with their different 
> wind load ratings, etc.  My initial thinking is to build a "platform" that 
> will tie into the roof members, spreading out the load, and giving me 
> multiple anchor points....say 10' x 10' covering 5 beams.  An engineer 
> will be consulted.


What about building a rigid pyramid to support a free standing tower. 
Because the members are rigid they can carry both compression and tension 
loads (as opposed to tension only guys).  The members could be something 
like pipe, and probably wouldn't need to be all that tall, and might be 
invisible from the ground (particularly if there's a parapet around the roof)

What you're really looking to do is to carry the overturning forces on the 
tower to multiple roof members.

This would be a lot lighter weight (for a given strength) than a flat plate 
platform.

The other approach would be to make the platform a truss, supported some 
small distance off the roof, which is anchored to the beams under the roof 
at the appropriate places.  The design would be a big more sophisticated, 
but, think of it in these terms:

A 40 foot freestanding tower can transmit all the bending loads to the base 
and isn't particularly huge.  Now, imagine that tower laid on its 
side.  Assume a perfectly rigid tower sticking up and attached perfectly 
rigidly to your laying down tower.  The loads on the laying down tower are 
basically the same as they were in the previous case, and you could 
transmit the entire bending load to the other end of the tower without failure.

In reality, your truss wouldn't need to be anywhere as big as the tower: 
you've got multiple places of support, for one.




> If you have mounted a tower on a roof, I'd like to hear what you have to 
> say and any tower manufacturer recommendations you may have!  I was 
> thinking about aluminum in order to keep the weight down to a 
> minimum.  Another option was a guyed Rohn 25G.
>
> When I was Chief Operator for Naval Station Long Beach MARS Station in 
> 1990, we had a crank-up tower mounted over a single beam and guyed.  I 
> didn't install it, but I had to work on it!
>
> I would rather NOT have to run guy wires in order to keep the "looks" clean.
>
> As always, THANK YOU!!!
>
> Dino...k6rix@earthlink.net
>
> _______________________________________________
>
> See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless 
> Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with 
> any questions and ask for Sherman, W2FLA.
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk

_______________________________________________

See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any questions and ask for Sherman, W2FLA.

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