[TowerTalk] 50' on 12" slab

[Roger Borowski]

Mike, Although 12" thick concrete may seem fairly substantial, concrete has
tremendous compressive strength but little in the way of tension or bending
strength. I would suggest if this is a plan you would prefer, to have the
tower mounting pattern concrete core drilled all the way through and in
addition to using long enough grade 4140 threaded rod with double nuts and
washers for your tower mounting. I'd also recommend a minimum 3/4" thick
cold roll steel plate approximately 4 ft square also drilled for the tower
mounting pattern in its center area and hoisted in place under the balcony
slab. With the concrete sandwiched significantly with steel and the tower
base, any movements at the tower would be putting the mounting in a safe
compression mode, rather than tension. With a thick and large steel
reinforcement plate, any movements or bending will be minimized, which is of
utmost importance. I realize that this will add significantly to the cost of
this installation,  but it would be the only really safe way as I see it
unless you have a really flimsy tower with very little antenna and overall
wind load. In that case, possibly lesser measures might be safely attempted.
It may be wise to contact a structural engineer in your area for his
evaluation for your exact application. I believe it would be money well
spent as I also see the sealing and flashing the roof around the tower to be
problemsome and that is something totally out of my arena of expertise.
One other item of importance is the consideration of grounding for lightning
protection. Although it may be possible to accomplish this with heavy and
wide copper stripping at the tower from above the roof, it could be a
compromise as to protect any equipment attached to the tower antennas and
rotator?, those cables must all come down to ground level also for lightning
protection. The 70 ft. tower in a typical full manufacturers recommended
foundation at grade level may become the more viable alternative considering
all the aforementioned. It certainly solves most all of the above ground and
through roof engineering considerations. Most anything is possible but many
not real feasible.
Best Wishes, -=Rog-K9RB=-

----- Original Message ----- 
From: "Mike Wrigglesworth" <mike.wrigglesworth at soundprint.com>
To: <towertalk at contesting.com>
Sent: Tuesday, August 19, 2003 6:37 PM
Subject: [TowerTalk] 50' on 12" slab


>
> Hello,
>
> I'm hoping to install a 50' self-supporting tower onto a 12" concrete slab
> that is a balcony on a building within a plant.  The balcony is 17' above
> grade and has a surface 12' x 17'.
>
> Is this possible or will I need to install a 70' tower in a full
foundation
> at grade?
>
> Any thoughts are greatly appreciated.
>
> Regards,
>
> Mike
>
>
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