This thread has been going on for a while and I forgot the original
question. I don't recall anyone saying this is for a self supporting
tower. If it is for a guyed tower and he's building it to Rohn's specs,
than I see no problem with separate pours as the lower section IS just a
footing.
John
>
>----- Original Message -----
>From: "Red" <RedHaines@centurytel.net>
>To: "Towertalk" <towertalk@contesting.com>
>Sent: Wednesday, December 04, 2002 12:40 PM
>Subject: Re: [Towertalk] Pouring base of tower
>
>
>
>
>>Chuck is correct regarding the direction of stresses, and that the pier
>>must be fastened to the base or it will overturn on top of the base.
>> However, it is not difficult to achieve that with the re-bar,
>>especially if the re-bar is anchored in the concrete with J bends at
>>each end. Calculate the overturning moment at the junction (overturning
>>moment at the tower base minus the righting moment of the pier) and use
>>that difference to calculate the tension that may appear in the re-bar.
>> Do not place the re-bar too close to the outer surface of the pier; 3"
>>absolute minimum, 6" insures against variables. The moment that each
>>re-bar can support is the yield (not ultimate) strength of the re-bar
>>times its distance from the center of the pier.
>>
>>Putting the J bend at each end of the re-bar is easily accomplished with
>>a 'rod buster', a tool available at contractor supply firms that both
>>cuts the re-bar and bends it. I recently priced one at about $200,
>>manually operated. No local rental agencies offered one.
>>
>>I bought the re-bar from a local ready mix supplier, already cut to my
>>specifications. I didn't put in the J bends, as I used a single pour
>>and had welded cross members on each of the vertical members, so each
>>vertical member had its full length engaged with the concrete and had
>>several welded cross members giving it additional grip on the concrete.
>> The tower manufacturer didn't specify any re-bar and the tower base
>>legs have welded lugs to grip the concrete. I added the re-bar
>>primarily to make a UFER cage; any additional strength was a plus.
>>
>>73 de WOØW
>>
>>Chuck Lewis wrote:
>>
>>
>>
>>>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.
>>>>>>_______________________________________________
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>>>>>>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
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>>>>>http://lists.contesting.com/mailman/listinfo/towertalk
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
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>>>>AN Wireless Self Supporting Towers at discounted prices,
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>>>>
>>>>Wireless Weather Stations now $349.95. Call Toll Free,
>>>>888-333-9041 for additional information.
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>>>>
>>>>
>>>>
>>>>
>>>>
>>>
>>>_______________________________________________
>>>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.
>>>_______________________________________________
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>>>
>>>
>>>
>>>
>>>
>>
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>>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
>>
>>
>>
>>
>
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>
>
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>
>
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