Wait a minute!!!
This application is NOT like a footing! I hope someone with some credentials
will chime in here and keep us from doing some dumb stuff! Footings do not
have to withstand overturning moments, and your freestanding tower base
does. The tower base does more than simply support the weight of the tower,
and the tower is not held vertical simply because of the weight of the base.
When the wind tries to tip the tower, the small 'pier' is pulled up and away
from the large 'pier' on the windward side. The large 'pier' is hooked under
several feet of (hopefully) undisturbed soil, and the two chunks of concrete
are being pulled apart. Now there might indeed be an epoxy or similar
compound or a rebar configuration which will give the two pours the tensile
strength of a single pour, but you need to ask the question relative to a
tower base, NOT a foundation/footing, and the answer needs to come from the
right source. Your concrete contractor no doubt knows a great deal about
foundations and footings, but I'll bet he knows diddley-squat about TOWER
BASES. Neither do I, for that matter, but let's not make the mistake of
thinking that if it looks just like a foundation/footing it can be treated
as a foundation/footing. These are two distinct applications despite the
fact that they LOOK identical. Tower bases have a unique set of requirements
which include a combination of compressive, tensile and shear loads, but a
foundation/footing is mostly compressive. Didn't the manufacturer specify a
SINGLE pour? Why?
Please check with someone who knows about TOWER BASES!
Chuck, N4NM
(hoping someone who knows about TOWER BASES will tell me I'm full of cr*p)
----- Original Message -----
From: "Phil - KB9CRY" <kb9cry@attbi.com>
To: "TowerTalk" <towertalk@contesting.com>
Sent: Tuesday, December 03, 2002 9:30 PM
Subject: Re: [Towertalk] Pouring base of tower
> Well I finally talked to my industrial concrete contractor and described
> the original question. He told me that the pier on a larger pier is
> just like a footing/foundation wall design and as long as the rebar ties
> the two pours together, one does not normally use an epoxy bonding agent
> between the two. If one if worried about water seeping in the cold
> joint and attacking the rebar, then normally epoxy coated rebar is
> specified. The bonding agent would certainly work but it is overkill.
> So I stand corrected and now slightly more educated. Hope this helps
> others too. Phil KB9CRY
>
>
>
>
> Guy Olinger, K2AV wrote:
>
> >I think you're a little off on this one, Steve.
> >
> >In construction of all concrete framed buildings, pours separated by
> >weeks and having rebar in common are all over the place, and have to
> >be. They occur at the boundary of floors and columns.
> >
> >The floor above cannot be poured until the one below has hardened to
> >the strength to carry the weight of the one above.
> >
> >There are simple, common, well-documented steps that are always taken
> >at pour boundaries by professionals, no more mysterious than the
> >vibrator used to eliminate voids in the pour.
> >
> >That it's not bandied about much on Towertalk merely reflects that
> >double pours are commonly not needed for amateur towers, not that
> >there's anything wrong with them.
> >
> >The base for my Trylon was designed by a fellow that does building
> >foundations. It was done in two pours so that we could stand the base
> >and bottom section on a firm surface, shim it to vertical and tie the
> >base directly into rebar aligned to the desired orientation (one face
> >edge on to 45 degrees).
> >
> >When the rest of the base was poured, the bottom section was securely
> >positioned by angled rebar across the square and fastened to the base
> >legs, no possibility of movement, and an automatic UFER ground.
> >
> >The layers were joined by a generous coating of some nasty epoxy stuff
> >put down the morning of the second pour.
> >
> >The base itself was an interesting 11 cubic yard over-engineered
> >design that forces the base to be lifted out of the ground and kick
> >sideways into undisturbed hardpan in order to be overturned. The tower
> >could be ripped off the base by a tornado, but the base is never going
> >anywhere. If I move, the base will be marketed as a pad for an
> >incinerator or large outdoor barbeque.
> >
> >When I asked the guy about the double pour and seepage, he just looked
> >at me like I was crazy, and my contractor son-in-law gave me one of
> >those shut-up-before-you-embarrass-me looks.
> >
> >Just because there's a wrong way to do something doesn't mean it
> >shouldn't be used.
> >
> >73, Guy.
> >
> >----- Original Message -----
> >From: <K7LXC@aol.com>
> >To: <wz7i@arrl.net>; <towertalk@contesting.com>
> >Sent: Sunday, December 01, 2002 11:04 AM
> >Subject: Re: [Towertalk] Pouring base of tower
> >
> >
> >>In a message dated 11/30/02 4:51:50 PM Pacific Standard Time,
> >>
> >wz7i@arrl.net
> >
> >>writes:
> >>
> >>>I am planning the installation of a self-supporting tower. My
> >>>
> >contractor
> >
> >>> asked me a question to which I don't know the answer. Is there
> >>>
> >any reason
> >
> >>> why he cannot pour the base in two pours as long as they are tied
> >>>
> >together
> >
> >>> by the rebar cage? The plans call for the foundation to be 9 x 9
> >>>
> >at the
> >
> >>> base and then 5 x 5 at the surface. He would prefer to pour the
> >>>
> >18" thick
> >
> >>> 9 x 9 foot section before the 5 x 5 foot section. Any reason why
> >>>
> >not?
> >
> >> It should be in one pour so that the base is totally bonded
> >>
> >together. If
> >
> >>the bottom pour has 'gone off' and hardened, you wind up with two
> >>
> >separate
> >
> >>layers.
> >>
> >> Sometimes there are two pours if you have to have two trucks
> >>
> >worth of
> >
> >>concrete but they are poured consecutively with little or no time
> >>
> >delay.
> >
> >> Are you looking at something like a pedestal base where it's not
> >>
> >a cubic
> >
> >>hole? Did you take the manufacturer's specs or have a PE design it?
> >>
> >Sometimes
> >
> >>manufacturer's specs are pretty impractical (i.e. Trylon's undercut
> >>
> >base, US
> >
> >>Tower's deep skinny holes) so it'd probably be easier if you could
> >>reconfigure it for simplicity's sake. The problem is that the bases
> >>
> >are
> >
> >>designed by engineers sitting in an office somewhere and they never
> >>
> >have had
> >
> >>to install one of their (stupid) designs.
> >>
> >> What kind of contractor wouldn't know the answer to your
> >>
> >question?
> >
> >>Cheers,
> >>Steve K7LXC
> >>TOWER TECH
> >>_______________________________________________
> >>AN Wireless Self Supporting Towers at discounted prices,
> >>See http://www.mscomputer.com
> >>
> >>Wireless Weather Stations now $349.95. Call Toll Free,
> >>888-333-9041 for additional information.
> >>_______________________________________________
> >>Towertalk mailing list
> >>Towertalk@contesting.com
> >>http://lists.contesting.com/mailman/listinfo/towertalk
> >>
> >
> >
> >_______________________________________________
> >AN Wireless Self Supporting Towers at discounted prices,
> >See http://www.mscomputer.com
> >
> >Wireless Weather Stations now $349.95. Call Toll Free,
> >888-333-9041 for additional information.
> >_______________________________________________
> >Towertalk mailing list
> >Towertalk@contesting.com
> >http://lists.contesting.com/mailman/listinfo/towertalk
> >
>
>
>
> --- StripMime Report -- processed MIME parts ---
> multipart/alternative
> text/plain (text body -- kept)
> text/html
> ---
> _______________________________________________
> AN Wireless Self Supporting Towers at discounted prices,
> See http://www.mscomputer.com
>
> Wireless Weather Stations now $349.95. Call Toll Free,
> 888-333-9041 for additional information.
> _______________________________________________
> Towertalk mailing list
> Towertalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
>
|