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 XML Subscriber 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 XML Subscriber 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
    http://forums.qrz.com/showthread.php?t=176894&highlight=Rohn+Tower

    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.


    w9gb
     
    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" ! ! !
     
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