A couple more comments, some not covered before: (all comments w/o
engineering calcs - YMMV)
1. Square tube is stiffer/stronger than round pipe or wide flange beams
(I-beams) of same #/ft.. All of the small structurals suppliers I've
dealt with stock it in 4" x 4" and a standard length is 20', so cut in
half makes about the right length for supports. 0.25" wall is probably
ok, even more so when filled with concrete. 0.375" and 0.5" are also
commonly available, but will take some strength or rigging to handle.
Check the web tables for #/ft to be sure you can handle it.
2. As commented by others, sch 40 galvanized welded (water) pipe is not
strength rated, so not a good choice. Seamless and or DOM, structural,
or sch 80 would be better choices. Drill pipe is great also if you can
find some surplus in 4" or larger. (heavy wall, alloy steel)
3. The concrete bottom flange idea works if you have good soils on top
and compact it as it is backfilled. Otherwise, there is little
resistance to overturning until it reverts to "undisturbed soil"
conditions, about 3+ years. Filling the hole to the top with concrete
is better and is nearly full strength in a week.
4. Not mentioned is the need for rebar in all situations, mainly to keep
the concrete from cracking. So look at the tower base designs -
multiple rebar squares with at least 3" coverage of concrete and
vertical bars to tie them together. It seems unlikely that there will
be much rotational torque but welding a couple of tabs on the post and
making sure it is free of mill oils will help insure it stays stuck to
the concrete.
5. For small jobs like this getting stronger concrete is a trivial cost
- order 4000 psi.
6. Two data points - my 8' above grade solar panels are on 8" pipe
buried 9' in a 36" dia hole filled with 3500psi concrete - what the
county engineer required, but I think way overkill. My 5' high ranch
gates are on 4 x 4 x.25 steel tubes in 3' deep 18" diameter u-mix-it
concrete and have taken the side off a trailer without moving.
7. Another item not mentioned is to use a "dead man" anchor to back guy
the post. This could be a guy to the top of the post
and to a point 4' out from the base that has a concrete block anchor.
The weight in this case provides the secondary guy anchor and soil
conditions don't matter much. Frequently used by power companies that
need a guy above a road to a pole on the other side. Also, the ends of
fence lines use two posts tied together separated by 6' or so which
keeps the end post from tipping from the barbed wire tension.
The proper design calculations aren't difficult, a PE could do them in a
couple of hours, if you can find one willing.
Grant KZ1W
On 10/29/2011 10:59 AM, sgtokie@aol.com wrote:
> richard,
>
> your setup is totally different from mine but im gonna add in my
> info........1) 25g 90ft 1) 25g 130ft 1)55g 150ft (only 45ft in air for all 3
> so far)......i am using an elevated guy system at 9 anchor points ( on each
> tower) so when im on the tractor i can avoid guy wires.......i used 8"
> seamless pipe with 1/2" wall thickness that are 10ft in length.......i have
> 4ft of the pipe set in a 36" bore hole with concrete filled to ground level.
> i took 1/2x6" flat plate and cut 18" in length, on 1 end i drilled 3 holes
> for 3 sets of guys and on the 25g and 4 holes for the 55g for 4 sets of guys.
> i slotted the top of the pipe so the plate would sit at the average angle of
> the guys and welded 4 edges with 5/8' fillet welds. on the back edge i
> drilled 1 hole just in case i later want to back guy the post.....i made the
> elevated guy posts really heavy duty because im not an engineer. i had
> planned on filling the pipe with concrete but later decided not to and just
> welded a cap on. sorry i dont have a pic to send to you but when i go home on
> vacation i can send you one if you want.......................
>
> 9 years ago i did an elevated guy at my other house in town and i used 6"x1/4
> wall welded pipe on a 60ft 25g tower.......welded pipe is not very
> structually sound but seamless pipe is.
>
> there are a lot of stresses put on guy wires that directly affect the
> anchors. you can use trig to figure out the amount of force applied to 1 guy
> wire,,,,,,,,,,, sine=o/h.......cosine=a/h........tangent=o/h opposite,
> adjacent, hypotenuse............. just substitute in the expected force in
> your pathegream therom........... a squared + b squared = c squared to find
> the vertical, horizontal& diagonal force applied to the guy wire then just
> plug in the numbers and will give you pretty close to the forces you need to
> plan for. .......i over planned......
>
> i dont have all my notes with me or i would give you more info on my
> setup..........i do know there are several threads on here dealing with mast
> sizes and materials and you can apply the same rules to elevated guy anchor
> points.......most masts if they are 1020 DOM or 4120/4130/4140 crome
> molybdium steel are only 1/4 inch wall thickness and just support an antenna
> or a few have tremendous forces just from the boom& elements.......so in guy
> wires you have to add in the surface areas of the tower sections and
> rotor.......so im really lazy and just over engineered it
>
> i have seen a commercial tower site that used I beam (some call it H beam)
> and was a really nice setup as well but i got a good deal on the high
> pressure pipe
>
> remember rohn 25g guy wires are 3/16 with a preload of #400 pounds which is
> 1/10 (10%) of their anticipated breaking strength........myltiply 400 pounds
> times 4foot of pipe sticking out of the ground and it is 1600 pounds of
> stress at the base where the pipe is in the ground.........just something to
> think about.
>
> i know there are many more hams that are engineers and know 1000x more about
> the forces and equations than i do but just giving you my thoughts on your
> plans.
> sgtokie@aol.com
>
>
> Who’s yer Baghdaddy !
> Karrada district
> Baghdad, Iraq
> David Howard دايفيد
>
>
>
> -----Original Message-----
> From: towertalk-request<towertalk-request@contesting.com>
> To: towertalk<towertalk@contesting.com>
> Sent: Sat, Oct 29, 2011 11:48 am
> Subject: TowerTalk Digest, Vol 106, Issue 67
>
>
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> -----------------------------
> Message: 7
> ate: Sat, 29 Oct 2011 11:09:33 -0500
> rom: Richard<yvadir@gmail.com>
> ubject: [TowerTalk] pipe anchors
> o: towertalk@contesting.com
> essage-ID:<4EAC253D.9030905@gmail.com>
> ontent-Type: text/plain; charset=ISO-8859-1; format=flowed
> I live on a small city lot and am in the process of installing a 40 ft
> ohn 25G tower in my back yard with a pier pin base. I'd really like to
> void using screw in anchors in such close quarters and would prefer to
> se an elevated guy anchor like pipe set in cement. I originally thought
> hat 11 ft would be great to clear my roof line but have been told that
> ould require a pipe larger than what I can obtain around here. Revising
> y plans a 4 ft high pipe in the corners of the back yard would still be
> etter than going to ground level. Can anyone give me an approximate
> dea as to what size pipe and what size base might be needed?
> My tower is 40 ft, I would have at most 12 lbs of wind load on it, my
> oil is a pretty heavy clay with no sand and no rock at least down to 4
> t., our wind zone is said to be 70 MPH. Any input would be greatly
> ppreciated.
> 73
> Richard / N5YPJ
>
> -----------------------------
> Message: 8
> ate: Sat, 29 Oct 2011 12:48:00 -0400 (EDT)
> rom: Cqtestk4xs@aol.com
> ubject: Re: [TowerTalk] pipe anchors
> o: TOWERTALK@contesting.com
> essage-ID:<1632c.8a0ccf9.3bdd8840@aol.com>
> ontent-Type: text/plain; charset="US-ASCII"
> My GUESS would be that 4" galvanized pipe would work. I would sink it
> bout four feet in a base about 3 x 3 x 1.5 feet of concrete. That would be
> n a hole 3 x 3 x 4 so you would only fill the hole up 18 inches with
> oncrete and back fill the rest with the dirt from the hole. if it was in my
> ackyard, I would sleep well at night with the set up. You might be able to
> et by with less, but do you really want to try. Towers make a big boom
> hen they come down.
>
> he three anchor bases would need a total of 1.5 yards and your base for
> he Rohn 25 will need another yard or so. If your concrete company has a 5
> ard minimum (many do) simply pour the rest into the three anchor holes.
> hey will never go anywhere...for sure.
>
> s an extra you might want to dump concrete down the pipe...stops the pipe
> rom filling with water and adds some strength. If you do I would order
> he mud with small agregate for easier pouring.
>
> ill KH7XS/K4XS
>
>
> n a message dated 10/29/2011 4:09:54 P.M. Greenwich Standard Time,
> vadir@gmail.com writes:
> I live on a small city lot and am in the process of installing a 40 ft
> ohn 25G tower in my back yard with a pier pin base. I'd really like to
> void using screw in anchors in such close quarters and would prefer to
> se an elevated guy anchor like pipe set in cement. I originally thought
> hat 11 ft would be great to clear my roof line but have been told that
> ould require a pipe larger than what I can obtain around here. Revising
> y plans a 4 ft high pipe in the corners of the back yard would still be
> etter than going to ground level. Can anyone give me an approximate
> dea as to what size pipe and what size base might be needed?
> My tower is 40 ft, I would have at most 12 lbs of wind load on it, my
> oil is a pretty heavy clay with no sand and no rock at least down to 4
> t., our wind zone is said to be 70 MPH. Any input would be greatly
> ppreciated.
> 73
> Richard / N5YPJ
> *****************************************
>
> _______________________________________________
>
>
>
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