Free Standing Tower How Much Concrete?

Discussion in 'General Technical Questions and Answers' started by KD0FBK, Oct 11, 2008.

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  1. KD0FBK

    KD0FBK Ham Member QRZ Page

    So if you have a free standing tower of unknown manufacture, is there a formula of some sort as to how much concrete you should put in the ground to properly support the tower? :D
  2. WB8MKV

    WB8MKV Ham Member QRZ Page

    Yes, right on the side of the bag it says in large print " enough to fill the hole "
  3. K7MH

    K7MH Ham Member QRZ Page

    If it doesn't fall down in a 100mph wind then you used enough!

    No way to be sure other than IDing the tower which we do here on the Zed quite often. Got pictures??
    It's height will have a lot to do with it!
  4. KD0FBK

    KD0FBK Ham Member QRZ Page

    :D Ok how big should the hole be? This will be a 75' freestanding tower that is triangle shape with about a 3' foot-print.

    I was think 5x5x5 which will be around 16-17k pounds of concrete in the ground.
  5. KD0FBK

    KD0FBK Ham Member QRZ Page

    Here is the tower 35' of it. On the trailer is a 20', 10' and 5' sections. I have two more 20' sections. There is no identifing mark other than on each flange the length it stamped S20=20' S10=10' and S5=5'.
  6. K7MH

    K7MH Ham Member QRZ Page

    Patience OM, Someone will probably jump in and know what kind of tower it is.
    I'd bet on that! Think in terms of yards of concrete, not pounds.
    I have a friend with a 70 foot self supporting tower who has 10 yards of concrete in the ground. You may need to understand things like "lots of money", "concrete pump truck" and "backhoe"!
    5X5X5 is probably nothing for that tower. Mine is 3X3X6 for a smaller 40ft tubular tower that is self supported and tilt over.
  7. KA7GKN

    KA7GKN Ham Member QRZ Page

    Brian, safety is paramount here! There are significant forces involved when installing a free standing tower.

    Heed the advice given here and search to determine the make and model of your tower.

    If a building permit is required you will need engineering specifications of the tower!

    A 75 foot tower is a dangerous assembly if not properly installed.

    I have a 75 foot tri-ex self supporting tower. I had a hole delivered 4'x4'x8'
    per the instructions. The re-bar cage was installed properly and grounded and approved by the building inspector.

    Then 3600psi rated concrete was poured. I think I used 5 or 5 1/2 yards. The pour was vibrated to remove bubbles and properly cured before any installation was started.

    You will never properly install your tower if you think a few bags of quick mix will do!

    You may want to visit various tower manufacturer sites to try and identify your tower. you can also get a feeling on what is required to install a large tower from their other tower installation instructions.

    Finally carefully inspect your "new" OLD TOWER! If the tower has excess rust or damage you may want to think twice about installing it. Be aware of any hidden weaknesses such as poor welds or cracked braces hidden under paint!
    Also, contact your homeowners insurance company to discuss insuring the tower should it fall.

    Martin ka7gkn
  8. W9GB

    W9GB Ham Member QRZ Page

    Brian -

    An identical tower to this was posted (to ID) here in Q&A in the last 4 or 5 weeks. If you are impatient -- use the QRZ search and you can read those answers from the "years of wisdom" from W8JI, WB2WIK/6, K9STH -- who provided answers -- to that inquiry.
    Here is that link to original question by: W4ENT on September 24, 2008

    The Tower is NOT a Rohn 65 (G Series) ... which use a curve steel rod X-brace and weld to 3 outer tubes.
    What makes you think this tower was designed as self-supporting??

    BTW, Inspection of USED towers is paramount. Cracks, metal fatigue, corrosion is not unusual on towers > 25 years
    Some county and township boards now have permit requirements that you may not be aware of.
    Many of these laws and ordiances were quickly "put on the books" in early 1990s to avoid liability issues for governments -- after a rash of cellular tower accidents -- in which the installers and local citizens were injured and killed -- and poor inspections or no permits had been issued.
    FCC PRB-1 offers you NO protection for safety or FAA related requirements.
    Soil surveys are required in some parts of the country -- you are in tornado alley -- so wind requirement of 100 to 120 mph for installation -- would be expected.

    Last edited: Oct 11, 2008
  9. K9STH

    K9STH Ham Member QRZ Page

    From what I can see, the tower was NOT designed to be self supporting. Self supporting towers are tapered. That is they are much larger at the bottom and generally each section is smaller at the top than the next one. Those in the photo seem to be the same size all the way.

    A quick "guess" is that the tower is Rohn 55 or Rohn 65. But, there are other towers that are similar in construction.

    Glen, K9STH
  10. AG3Y

    AG3Y Ham Member QRZ Page

    That looks to me like a situation where I would definately NOT consider "doing it myself" ! ! !
  11. W9GB

    W9GB Ham Member QRZ Page

    Here is Tom, W8JI web site for his Rohn 65G install. NOTE: Look carefully and you will see this tower is NOT constructed like yours, but design is not too different. Rohn 65G is a GUYED tower. Pole Rohn 65G.htm

  12. NA0AA

    NA0AA Ham Member QRZ Page

    While you are getting all sorts of good advice, one general remark is that any tower of the same height with the same loading would generally require the same size anchorage....IOW, for a rough-cost estimate purposes, I'd look for a similar height tower and look at their on-line data - I believe US towers and Rohn will both give you standard data you can use to estimate the job before you have it engineered.

    But engineered it must be if you plan to keep your insurance coverage.

    Unless this used tower is in excellent shape, it might be more cost effective to buy new - the tower itself is a small part of the total cost of a tower installation. For one thing, the engineering will be more certain and therefore cheaper.
  13. KA5S

    KA5S Subscriber QRZ Page

    Looks like a Swager glide slope antenna tower. Sections are labelled the same, too.

    Added in edit:
    If it is, their Glide Slope Towers page shows the base assembly as needing a nine foot by nine foot concrete base three feet deep. See Slope/GLSP-03.pdf

    Call Swager.

    Last edited: Oct 12, 2008
  14. W9GB

    W9GB Ham Member QRZ Page

    The Glide Slope models are only sold as a 35' or 50' tower.
    SO -- it appears you have the 35 foot model. Slope/GLSP-02.pdf

    Swager Communications, Inc.
    P.O. Box 656
    Fremont, IN 46703
    Toll-Free: 800-968-5601
    Fax: 800-882-3414 • 260-495-4205


    Swager Notes:
    TIA/EIA-222-F-1996 STANDARD, -OR- 120mph 3-SECOND GUST WIND

    3,000psi AT 28 DAYS.



    Last edited: Oct 12, 2008
  15. W9GB

    W9GB Ham Member QRZ Page

  16. KU0DM

    KU0DM Guest

    Brian, I notice you are from Paola.

    I am just north of you in JoCo, I would highly recommend talking to KC0NYS (you probably already know him) or KC0BS.

    Both are highly knowledgeable when it comes to towers, and there will more than likely be group of Miami county guys and Brian and myself who'd be willing to help you put it up if needed.


    --Duncan, KU0DM
  17. W8JI

    W8JI Ham Member QRZ Page


    You really have to check with the manufacturer. As others have said, don't think of it as weight of concrete. Weight doesn't do much. It is the surface area pushing against the dirt and trying to compact or move the dirt that gives it all the strength.

    One thing to keep in mind. Although the tower is BIG and can probably take 60 feet unguyed, the stresses on the base are even bigger. All that tower, since it is not tapered to a point, will have quite a bit of wind load at the top even without antennas. That means you will have a great deal of pressure compressing and tensioning the bolts at the base flange.

    You will probably have to use some long J bolts that go down to the rebar in the concrete. We normally weld the base bolts to the rebar, and be prepared for some expense in the base.

    The good news is with only 60 feet you should be able to get a crane or boom truck pretty cheap (probably under $1000) and if the base is strong enough (check with the manufacturer) you should be able to put almost anything you want on top.

    Just be careful, a big tower like that can do a lot of damage if someone drops it or gets a finger in the way while lowering the sections. You can probably lift it all in one piece if you rig it properly.

    Have fun, but please check with the manufacturer and see if it is safe and how big the base has to be.

    I like to guy my towers because they just sit on a pier without being bolted down, but not having guy lines is nice.

    73 Tom
  18. KD0FBK

    KD0FBK Ham Member QRZ Page

    Thanks Duncan, I actually just went to the the WSWA meeting last Wed night and met JD also talked to him on radio about a month ago. I haven't met KC0BS yet but I am sure I will.

    I will take all the help I can get when it comes time. I know I will have to put some work into this. The good thing is I can get a boom truck and a backhoe for nothing. As far as engineering goes I work for a mechanical / structural engineering company so it shouldn't be a problem.

    It won't go up for awhile as I am not even moved into the house it will be at yet! I don't mind having to guy it, really no big deal I have plenty of room for it.
  19. KD0FBK

    KD0FBK Ham Member QRZ Page

    Thank you W9GB, that is the exact tower I have, I will be calling Swager on Monday. I had already determined all the materials and they match the Swager drawings perfectly!

    I am in the process of building two more sections so I will call and see if Swager thinks I need a bigger base and/or guys lines. That particular tower according to them at 35' and 50' is an un-guyed tower.

    I plan on putting my Mosley Pro-67-B at the top, a couple of verticals hanging of the sides, and using the top and another tower I have to hang some long wires and dipoles.
  20. W9GB

    W9GB Ham Member QRZ Page

    Actually, you should thank Cortland, KA5S -- for a good eye!!

    Tim Swager is president.
    You can ask them about the design differences between the Swager 35 foot and 50 foot versions.
    BTW, Fremont, IN is near the Michigan, Indiana and Ohio border (along Indiana Toll Road / I-80, I-90).

    I never thought radio amateurs would be using these towers (due to $$ and usage largely for cellular and microwave installations).
    Seems that these are now being surplused in some areas (cellular upgrades?) --- as this is the third inquiry for this model in past few weeks -- here on QRZ.

    Last edited: Oct 12, 2008
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