Yeah, any sentence that starts with "messing with a tower foundation" is
likely to end with me saying "see a professional."
My unmodified tower base is overengineered and I know it, but at least I
know that it _is_ overengineered. Beats the crap out of "under".
Larry Wo0Z
On Thu, Jan 31, 2013 at 11:48 AM, Patrick Greenlee <patrick_g@windstream.net
> wrote:
> You need to go to the required lengths to ensure the new work is well
> attached to the old concrete. Drilling holes and doweling is a common
> practice. Use a large powerful hammer drill and carbide masonry bits. I
> prefer to drill into the existing concrete at say 10-15 degrees or more
> from square and in different directions of lean for the different dowels.
> This makes it harder for the dowels to pull out than if they were all
> parallel to each other.
>
> Thin caps (thin slab of concrete poured over the original concrete) are to
> be avoided as they often do not bond well and under stress will detach. An
> electric demo hammer (small electric jack hammer) can ne used to take off
> several inches of the original concrete surface. "Real" jack hammers are
> quite a handful weighing in at about 100 lbs but if you are young, spry,
> strong, and not terribly bright you can get the job done faster (or hire it
> done.) You then form up the new concrete pour. Weld plates sufficiently
> heavy duty for the loads expected can be placed in the new pour and then
> later welded to to attach tower mounting hardware. I'd consider a single
> large HD steel weld plate considerably larger in width and length than the
> footprint of the tower with several "J" bolts ("J" shaped rebar works well.)
>
> Drilling the added concrete and epoxying in bolts would not be my personal
> first choice. My personal first choice due to my experience (and lack
> thereof in some situations) is to lay out my ideas with sketches and submit
> them to a close personal friend who has a masters degree in mechanical
> engineering from UCLA and over 35 years hands-on experience. He sanity
> checks my ideas and sometimes suggests alternatives.
>
> I don't loan him out so I recommend you run any ideas you intend to
> incorporate by a PE. The most dangerous time for us is when we don't know
> that we don't know. Sometimes I resemble that remark but with luck I am
> usually smart enough to get appropriate help. I also have a friend with 35
> plus years in antenna design. They both consult with me when I do non
> standard things such as putting a Hy-Gain Hy-Tower vertical on top of my
> metal barn with no radials and no concrete base.
>
> Any $ saved by not getting some pro advice will pale in comparison to the
> potential losses if you have a mechanical failure.
>
> Best of luck to you and share with us what your approach turns out to be.
>
> Patrick AF5CK
>
>
> -----Original Message----- From: Jack Berry
> Sent: Thursday, January 31, 2013 11:43 AM
> To: towertalk@contesting.com
> Subject: [TowerTalk] Refitting existing concrete base
>
>
> Question: Does anyone have knowledge or experience adding concrete to an
> existing base to increase the mass and adding new anchor bolts? Bolts
> would have to be drilled and epoxied in the resulting base??
>
> I have a substantial base for an existing tower, ~ 2.7 yds of concrete.
> It's in use with a guyed 60' GM aluminum tower.
> I will replace this tower with a USTower 72' crankup that needs a 5x5x8 ft
> cube of concrete with different & more anchor placements.
> Current base is 5ft x 5ft x 6" pad on top of a 42"x6' deep cylinder of
> concrete. All is tied together with rebar, one pour.
>
>
> God Bless & 73!
> Jack - WE5ST
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