Thanks for the details Chris. That roof must be a bit better constructed
than some of the industrial buildings Ive installed on. I left the
calculations to the building owners consultants but structure weight was
always a prime question with them. In all cases they opted for 25G and the
biggest antenna was a TH-7 with a 6 el for 6 above it. A 2 el 40M was out of
the question with the engineers.
Ice and high winds is always a concern out this way also.
Enjoy that setup, next you can plan for tower #2.
Carl
KM1H
----- Original Message -----
From: "Christopher J Galbraith" <cgalbrai@umich.edu>
To: "'towertalk'" <towertalk@contesting.com>
Sent: Friday, August 17, 2007 4:14 PM
Subject: Re: [TowerTalk] Our club's (W8UM) new tower and antennas
> Hi Carl,
>
> In a nutshell, we went with 55G for extra tower capacity and a safety
> factor. With the icing and wind conditions we had to meet with our
> proposed
> antennas at this height above grade, 55G had some extra load capacity, 45G
> may have just been sufficient, and 25G was insufficient according to Rohn
> specs and our structural engineer's analysis. For comparison, a MonstIR
> on
> 40 ft of 55G was just barely allowable according to the engineer's (FEM I
> believe) model.
>
> In the initial structural engineering work we had performed, the actual
> tower weight was a far second-order contributor to the total axial load at
> the base. It was interesting (and surprising to me) that most of peak
> axial
> load comes from guy forces that are transferred to the tower base.
> Putting
> 1.5 inches of radial ice on each guy line really makes for some
> astonishing
> axial load figures. In the end, the base axial load was indeed the most
> important factor.
>
> Anyhow, we decided to stay with 55G and add a very small axial load in
> return for extra tower capacity (for future antennas, more severe weather,
> climber's peace of mind, etc.).
>
> 73, Chris KA8WFC
>
>
> -----Original Message-----
> From: jeremy-ca [mailto:km1h@jeremy.mv.com]
> Sent: Friday, August 17, 2007 12:51 PM
> To: Christopher J Galbraith; 'towertalk'
> Subject: Re: [TowerTalk] Our club's (W8UM) new tower and antennas
>
> How come the extra weight of 55G when 45G or even 25G would suffice for
> that
>
> small load. Ive been involved in several roof top installs at
> commercial/industrial sites and roof loading weight was always the primary
> concern.
>
> Carl
> KM1H
>
>
> ----- Original Message -----
> From: "Christopher J Galbraith" <cgalbrai@umich.edu>
> To: "'towertalk'" <towertalk@contesting.com>
> Sent: Friday, August 17, 2007 3:14 PM
> Subject: [TowerTalk] Our club's (W8UM) new tower and antennas
>
>
>> Gang,
>>
>> For your enjoyment, here are some action shots of our new W8UM roof-top
>> tower installation from 7/30/07. It is a 40 ft Rohn 55G tower on top of
>> the
>> 60 ft tall Electrical Engineering and Computer Science (EECS) building at
>> The University of Michigan:
>>
>> http://www.umich.edu/~umarc/projects/towerConstruction.html
>>
>> And one view from the ground on Michigan's North Campus:
>>
>> http://www.umich.edu/~umarc/photos/tower/views/tower_Beal.jpg
>>
>> The new tower and antennas have evoked some positive responses from the
>> engineering types in the vicinity ("it is huge!") and we hope it will
>> serve
>> as our most valuable visual recruiting tool (enticing students into the
>> W8UM
>> shack).
>>
>> The 4-el SteppIR at 105 ft is a DX killer on 20m (and should be on 14-30
>> MHz
>> when propagation improves) and the dipole seems to be doing well on 40m,
>> too.
>>
>> We originally were going with a MonstIR for the HF Yagi but ran into a
>> series of engineering problems. It is a long story, but our problems
>> were
>> mostly due to having structural engineers that did not have any
>> experience
>> with roof-top antenna installations. In the end, the 6-20m Yagi with
>> 30/40m
>> dipole was a good compromise between overall performance and
>> size/weight/cost.
>>
>> I sincerely thank everyone on the list who gave us excellent advice
>> throughout the design process. We learned a great deal in the year or so
>> of
>> putting the design together, and a lot of information came from list
>> members' valuable experience. As you'll note on the web page, Hank
>> Lonberg
>> and Matt Strelow had a lot to do with our success, too!
>>
>> Support your college amateur radio clubs!
>>
>> 73, Chris KA8WFC
>>
>> The U-M Amateur Radio Club (W8UM)
>> www.umich.edu/~umarc
>>
>> P.S. If you know any U-M alumni, please spread the word. We love to hear
>> from former W8UM (and W8PGW, W8AXZ, even 8AX!) ops.
>>
>>
>> _______________________________________________
>>
>>
>>
>> _______________________________________________
>> TowerTalk mailing list
>> TowerTalk@contesting.com
>> http://lists.contesting.com/mailman/listinfo/towertalk
>>
>
>
>
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>
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