Foundation For 100' Self Supporting Tower

 
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Old 12-30-2011, 10:37 PM   #1
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Foundation For 100' Self Supporting Tower


I have done several of these at 45 and 60 feet, not really too hard. Now I have been asked to bid a 100 footer. Calls for a nice big 4' by 4' by 5' base. Again nothing special, but the ground is my concern. Very sandy soil and water table at about 3 feet.

I put in a guyed tower in this soil this summer, and the water was a problem but I was able to get it in just fine. Self supporting is another animal and I need some ideas how to compensate for the soil conditions.
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Old 12-30-2011, 10:49 PM   #2
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Re: Foundation For 100' Self Supporting Tower


How is there not a Geo-Tech Report & and Engineer involved in this.

You doing it with by guess & by golly & a little Kentucky windage gonna find your arse in the wrong side of court proceedings.

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Old 12-30-2011, 11:04 PM   #3
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Re: Foundation For 100' Self Supporting Tower


yeah kinda wondering why an engineer is not involved....seems like these are not problems you should be solving...for liability reasons....but you already know this having participated in these discussions for a long time....
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Old 12-30-2011, 11:37 PM   #4
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Re: Foundation For 100' Self Supporting Tower


Residential, no inspection, and minimal prints. Basically a sheet that comes with the tower sections that give a brief discription. The GC is on the hook for liability, he thinks he knows every thing there is to know about this crap, but he doesn't.

I know enough to know I don't know enough, just looking for any experience that is deeper than mine.

I dont care if you think it is careless or whatever, its gonna go up with or without me so if you have some ideas about making it more stable, I'm all ears.

Thanks for your concern about my financial well fare, but I actually pay for that type of advise.
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Old 12-31-2011, 05:46 AM   #5
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Re: Foundation For 100' Self Supporting Tower


100 ft is a long way up. I wouldn't touch it without a stamped drawing.
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Old 12-31-2011, 05:57 AM   #6
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Re: Foundation For 100' Self Supporting Tower


cloud anchors
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Old 12-31-2011, 06:38 AM   #7
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Re: Foundation For 100' Self Supporting Tower


You should be asking an engineer who designed the tower not here... You need a design based on different load calculations,i.e wind speed, lateral loads, etc. I doubt you want to pull that wagon with out stamped and approved drawings.
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Old 12-31-2011, 07:52 AM   #8
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Re: Foundation For 100' Self Supporting Tower


I hear what you guys are saying, but I am telling you, its like building a chimney. If you have never done one before, all you have is a bunch of questions. Once you have a few under your belt, it is really not that complicated.

I am going to pass this one on to someone else, cause I don't know the soil well enough to know what would work or not. If it was on good soil, I would dig it Monday and have it poured by noon.
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Old 12-31-2011, 07:56 AM   #9
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Re: Foundation For 100' Self Supporting Tower


Just curious... What's it for? TV? Cell? Private/commercial?


3' watertable is kinda scary...
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Old 12-31-2011, 08:11 AM   #10
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Re: Foundation For 100' Self Supporting Tower


Personal use. The guyed tower I set the base for this summer is the guys business and he needed better internet than dial up. Once he experienced what high speed was like, he had to have it at his house two miles away.

The only thing that will see through the trees is a tower over the trees. Its gonna cost him plenty, I can tell you that. Money doesn't seem to be a big problem for this guy.
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Old 12-31-2011, 08:33 AM   #11
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Re: Foundation For 100' Self Supporting Tower


I would not pass on the project just yet.

The sheet that comes with the tower is probably based upon certain conditions, such as soil bearing capacity of 2,000 psf or some other conditions. You need to find out what those conditions are.

The cost to hire a geo-technical inspector to verify your site conditions is very little, and should be passed on to the owner. It is for his benefit to have a third party verify soil conditions.

If the soil is not up to minimum spec, you may have to dig deeper or make the footing larger.

The water table is easy to deal with, dig a pit near your tower site, a couple feet below the bottom of the footing elevation.
Drop a pump in and let it run, this will lower the water table and you can then have drier conditions to get your work completed.
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Old 12-31-2011, 08:49 AM   #12
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Re: Foundation For 100' Self Supporting Tower


You should be able to check w/ the manufacturer for details, but for me the pad seems insufficient; It is a very long lever arm sitting on something relatively small; a slab buried in wet ground. The amount of wind a 100 foot tower catches is much greater than a 60. I would think guy wires might be in order. (meaning other footings?)

Think of this scale; attach a 10 foot pipe to a brick buried at ground level. : ) It would fall down, wouldn't it?

I think you are buying a lot of liability for a relatively small price.

http://www.glenmartin.com/catalog/page9.html
shows a 50 foot tower requires a 4 x 4' footing and guy wires. (I infer that means a bigger footing for a 100 footer)

I have to agree; you are the concrete guy, not the engineer. This is an engineering issue, from slab dimensions, to reinforcing steel to soil type. Further, around here there are permits that must be applied for and (seems like 1.33% fall zone) site approval.

good luck
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Old 12-31-2011, 09:08 AM   #13
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Re: Foundation For 100' Self Supporting Tower


willy,
There are self supporting towers and guyed towers. You may have heard of the Eifel tower in France? It is all a matter of design and cost of construction. 100' self supporting are pretty spendy but in this situation, that is not the issue.

The guyed tower that I set this summer had a 3' X 3' base aprox. 3 feet deep. The guy anchors were 2' diameter and about 4' deep and water came in as fast as I could pump it out. Because of poor communication, that tower had to be moved and when they pulled the bases, they were exactly as designed and very solid.

Tgeb,
I would really like to have an idea about the actual bearing of the soil. That would be a start. At this point, I am probably not going to drive 30 miles to check it out, cause I am not experienced enough with the soil type to know how to adjust. I am not even comfortable digging the hole, cause I know it will be very unstable and likely to colapse before I can get the cement in. Just a whole bunch of variables outside of my normal environment.
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Old 12-31-2011, 11:21 AM   #14
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Re: Foundation For 100' Self Supporting Tower


A retaining wall over 6' needs a stamp, you are kidding me if you think you dont need an engineer.
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Old 12-31-2011, 03:24 PM   #15
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Re: Foundation For 100' Self Supporting Tower


I'd like to see a pic of this tower - 4x4x5' seems ridiculously undersized.

If money is no issue as you say- have a geo-guy out on the customers dime and tack on 20%...You are in business to make money and do it right, no?
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Old 12-31-2011, 06:27 PM   #16
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Re: Foundation For 100' Self Supporting Tower


Quote:
Originally Posted by superseal View Post
I'd like to see a pic of this tower - 4x4x5' seems ridiculously undersized.

If money is no issue as you say- have a geo-guy out on the customers dime and tack on 20%...You are in business to make money and do it right, no?
sounds about right except that this is just a bid....which complicates things as you can imagine.

I'd like to see the BP's or some sort of picture as well....not that I could be much help.
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Old 01-01-2012, 07:07 PM   #17
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Re: Foundation For 100' Self Supporting Tower


It's a new aluminum tower from Rohn. I don't even think they have it on the web site yet. About 300 lbs, designed for a bottom hinge. They claim three guys can raise and lower.

Actual spec. on the base is 3 X 3 X 4 but the GC wants 4 X 4 X 5. I did get a soils map and it is just sand, no muck or high water table, so maybe I can do this after all. We put together an initial estimate Saturday and I think it is going to the HO Tuesday.

I did find some fairly extensive footer details on-line and basically they widened the base just like burying a top hat. Add a bunch of bar and you have a tower base.

Kentucky windage? Maybe, but after seeing the whole layout, I am a lot more comfortable with the project and putting my name on it.

Edit, money isn't a problem for the HO, but margin is always important, and I think we may have found some on this one.
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Old 01-01-2012, 10:19 PM   #18
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Re: Foundation For 100' Self Supporting Tower


And no guy wire - pretty amazing...my 20 ft flagpole gets whipped in the wind even when flagless

Cant really imagine this at 100 ft. - must sway a helling

3lbs per ft seem like a flagpole install to me.

You gotta post some pics of this... I'm dying to see it action

And yes...tophat footing would add tremendous rotation protection I would surmise.

We need our resident engineer to check in...where you at Dick?
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Old 01-01-2012, 10:51 PM   #19
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Re: Foundation For 100' Self Supporting Tower


He is cooling his boz in an ice house right now nursing the vikings 3-14 season.

I will believe it when I see it, but it is supposed to be good for 70 mph winds with ice buildup. I will not be climbing it.
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Old 01-02-2012, 11:25 AM   #20
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Re: Foundation For 100' Self Supporting Tower


Just so happens my company owns 20 guyed 90foot towers and one self supporting. We have 200 towers for clients. You want me to ask something from the engineer who did the self supporting tower? turns out he is buying bricks and borrowing a mason next week. although none of ours are in an area with groundwater.

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