Bert:
What I did on my crank up 50 ft W51 TriEx 50 ft tower
was expand the base by 1 foot in each direction. I
always figure a little more concrete won't hurt and
give it a little more support. Also what I did was to
hire a professional tower installer (well worth the
money since he took care of everything) who used
what's called "six sack mix" supposedly the same
consistency concrete used in interstate highway
bridges.
Since my area is permeated by small underground
springs he dug the hole, set the forms and base and
had the concrete in before the springs could leak much
water in the hole (this was in 1993). Earlier I had a
friend of mine who owed me a favor and who owned a
backhoe dig the base 5x5x6 and by the next morning it
was filled up with water. We pumped that out and
filled it in and moved over a few feet. Then I called
on professional help.
My concrete base looks just as good today, some 15
years later, as the day we poured it. The tower and
base have survived several 50-60+ mph gusts during
thunder and lightnihg storms when there was no way I
was going out in that WX and crank it down. I
originally had a Mosley Classic 33 WARC with the 40m
kit and an Isopole 2m antenna on top. I've since
changed to a Tennadyhne T10 log periodic and a
Cushcraft AR270B (the longer one) 2m/440 antenna that
sits at about 65 ft.
73 de Tom, WW5L
--- Gene Smar <ersmar@verizon.net> wrote:
> Bert:
>
> In situations like yours (little experience,
> seeking outside help), I would suggest following the
> LXC Prime Directive: Do what the manufacturer says.
> What does the tower manufacturer tell you to do for
> a base? You ought to check their web site either
> for the information itself or for a source to find
> same.
>
>
> 73 de
> Gene Smar AD3F
>
>
> From: Bert Almemo <balmemo@sympatico.ca>
> Date: 2008/09/02 Tue PM 06:47:32 EDT
> To: towertalk@contesting.com
> Subject: [TowerTalk] Dimensions of a tower concrete
> base
>
>
>
> Hi guys,
>
> Thanks for all responses, comments and suggestions
> regarding the dimensions
> of a concrete base for a tower or other support
> structure.
>
> It seems almost everyone wants to elaborate on the
> issue and also wants to
> put my question into different scenarios. Again, not
> being a structural
> engineer, isn't there a general rule as to what
> design provides the best
> support for a free standing tower or similar
> structure regardless of other
> circumstances?
>
> I was hoping to get some indication from the experts
> on TT which way to go
> as I'm not spending thousands of dollars to use the
> services of a structural
> engineer. I just want an opinion from you
> experienced guys. It's only a 55ft
> free standing tower with a medium sized tri-bander
> on top. So far I'm more
> confused than when I started this thread. Thanks.
>
> 73 Bert, VE3OBU
>
>
>
>
>
> -----Original Message-----
> From: towertalk-bounces@contesting.com
> [mailto:towertalk-bounces@contesting.com] On Behalf
> Of kr7x1@verizon.net
> Sent: Tuesday, September 02, 2008 12:24 PM
> To: Al Williams
> Cc: towertalk@contesting.com
> Subject: Re: [TowerTalk] Dimensions of a tower
> concrete base
>
> Hi Al:
>
> In the case of a cantilever (free standing)
> structure say like a ham tower,
> the wind or seismic force developed is horizontal
> (lateral). This force
> creates a cantilever moment at the base equal to
> w*L^2 / 2 where w is the
> lateral force per unit length and L is the height of
> the structure. This is
> the cantilever moment at the base. The lateral load
> also has to be resisted
> by the base along with the moment. The base
> horizontal (lateral) reaction is
> w*L. Then the weight of the structure also creates a
> force to be resisted by
> the base which is the weight of the appurtances
> (antennas, rotators,
> feedlines, the foundation weight, north facing fake
> owl, etc).
>
> Thus the base (foundation) needs to be designed to
> resist the vertical load
> of the structure, the lateral load and the
> cantilever moment due to the
> horizontal wind or seismic enviromental loading.
>
> In a nut shell, the foundation has to resist being
> pushed into the ground,
> moved through the ground and rotated in the ground
> all at the same time.
>
> Foundation strength or resistance to the applied
> loading is totally a
> function of the soil characteristics at the location
> being considered.
> This is the big variable. The IBC has a table that
> gives conservative
> generalized values to use for these soil
> characteristics if a geotechnical
> analysis and report is not available for the
> specific location.
>
> Regards
> Lonberg Design Group, Ltd.
> H.S. Lonberg, P.E.,S.E.
> President
>
>
>
> On Tue, Sep 2, 2008 at 8:18 AM, Al Williams wrote:
>
> > Please explain the difference between "lateral
> force" and "the moment
> > inherent in this type of structure"
> > and how they effect on tahe strength of the
> foundation.
> >
> > k7puc
> >
> >
> > ----- Original Message ----- From: "Hank Lonberg"
> <kr7x1@verizon.net>
> > To: "'Bert Almemo'" <balmemo@sympatico.ca>;
> <towertalk@contesting.com>
> > Sent: Monday, September 01, 2008 9:14 PM
> > Subject: Re: [TowerTalk] Dimensions of a tower
> concrete base
> >
> >
> >> Bert:
> >>
> >> The best answer to your generalized questions is;
> it depends.
> >>
> >> Depends if the foundation is supporting only
> vertical load as in a
> >> guyed structure.
> >> Depends if the foundation is to support a
> cantilevered or free
> >> standing structure with both lateral force,
> vertical force and the
> >> moment inherent in this type of structure.
> >> Depends if the designer is trying to utilize a
> spread footing type of
> >> foundation.
> >> Depends if the designer is trying to utilize a
> post type of
> >> foundation.
> >> Depends heavily on the soil's characteristics and
> strength that you
> >> are trying to utilize.
> >>
> >> So you see, your question does not have a closed
> form of solution,
> >> but depends on what you are trying to accomplish
> and what type of
> >> loading the structure you are trying to support
> will impart to the
> >> foundation.
> >>
> >> A case can be made for either the shallow spread
> footing type of
> >> foundation or the smaller footprint deeper
> foundation. The trick is
> >> to size them adequately for the loading condition
> versus the soil
> >> conditions expected.
> >>
> >> Gut level, the amount of concrete for either
> design is most likely
> >> similar.
> >>
> >> Regards
> >> Lonberg Design Group, Ltd.
> >> H.S. Lonberg, P.E.,S.E.
> >> President
> >>
> >> -----Original Message-----
> >> From: towertalk-bounces@contesting.com
> >> [mailto:towertalk-bounces@contesting.com] On
> Behalf Of Bert Almemo
> >> Sent: Monday, September 01, 2008 8:51 PM
> >> To: 'Bob Maser'; towertalk@contesting.com
> >> Subject: Re: [TowerTalk] Dimensions of a tower
> concrete base
> >>
> >> Hi Bob,
> >>
> >> Thanks for your reply. Yes, I think you missed
> the point.
> >> Sorry! I'm talking
> >> about the concept in principle not if the total
> weight is exactly the
> >> same.
>
=== message truncated ===
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