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Can Someone Help an Old Timer whom would like to Lift his Communications Tower?

  1. Oct 18, 2010 #1
    I am getting a bit older, and I have a Aluminum Communications Tower, and used to angle it up by myself from the back of the house to the side. Now I would like to lift the tower to its vertical position on the side of the house using the existing aluminum angled bracket plasma welded to a aluminum plate with six stainless bolts through siding and three 2x4s (Part of the framing of the house) at a height of 17 Ft. and 4 inches, pulley, a steel cable, and winch.
    Here are the variables;
    Aluminum tower weighs 100Lbs.
    Height is 21 Ft. 2" in the collapsed position.
    The tower tilts at the bottom of the base from near horizontal to its vertical position.
    At the tower's vertical point is the plasma welded side bracket, and is where I would like to place a stainless steel pulley.

    My Questions:

    1 - Since the aluminum bracket is mounted to the side of the house perpendicular to the tower to lift, some lag bolds will see greater stress than others, how much force is exerted, worse case, on the pulley and plasma welded side bracket on the side of the house? pull in Lbs.?
    2 - What strength stainless steel cable should be obtained?
    3 - Can the winch be mounted on the same tower 2 or 3 feet above the base efficiently?
    4 - What would be the formula (is this a Derrick Boom)?
    5 - Are there any other concerns to be considered?

    Even simpler, we have Triangle, A, B, and C; ----> A is the Base, B is the wall mount bracket, C is the end of the tower. Leg A and C weight is 100 Lbs. Height from A to B is 17 Ft. and 4 inches vertical, the distance from A to C (Horizontal Tower) is 17 Ft. and 4 inches as well since the cable will be also connected at 17 Ft and 4" making it an Isosceles Triangle.

    What is the Worse Case Stress on the Cable going from B to C and Pulley as the tower gets cranked up?
     
  2. jcsd
  3. Oct 19, 2010 #2

    nvn

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    mar128a: Are you sure about the tower weight value you listed? Are you sure you gave us the tower total weight, listed in the tower specifications? Is this tower a pole? Or is it a lattice structure? If it is a lattice structure, what is the tower width dimension?
     
  4. Oct 19, 2010 #3
    Hello,

    Yes the tower is a Lattice type made of aircraft aluminum with a width of 14.5" outer section, the inner is 9.5". The name of the tower is; "Aluma Towers" T-40-H, its actual weight is 72 Lbs. To make the math easier, I picked 100 Lbs. since the additional antenna would increase the weight some.

    When I first constructed the base back in 1991, I should have build a structure to support the tower in between two poles and pivet it about 5 or 6 feet up, that would have been ideal. Instead I opted to pivet the tower at the base, thus not being able to take advantage of the counter weight the tower would have presented.
     
  5. Oct 19, 2010 #4

    nvn

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    mar128a: Answers to post 1: (1) 611 N (137 lbf) at an angle of 58.9 deg below (measured from) horizontal.
    (2) Stranded, stainless steel cable having a diameter of up to 1.58 mm. Since cable strength slightly varies among manufacturers, if you eventually select a specific cable, we could check the particular specifications.
    (3) Yes.
    (4) There are many formulas. I choose to skip this question. The maximum (worst case) force during lifting (item 1) occurs when the tower is horizontal.
    (5) Tower still needs to be connected to house after lifting. It cannot be connected only by the lifting cable. The lifting cable is only for lifting.

    Footnote: Item 2 does not yet consider the cable termination connector strength, because I do not know exactly which termination connector you will use. Look for cable manufacturers design guides that state how to compute the termination strength relative to the cable nominal tensile strength (also called breaking strength); or call manufacturers technical staff. Let us know what you find. E.g., Sava Industries cable http://64.201.227.3/sava/sava_cat.pdf (4.7 MB pdf download) fairly clearly states the specific strength of the various terminations, but only when swaged by Sava. Therefore, it depends on what you select.
     
    Last edited by a moderator: Apr 25, 2017
  6. Oct 20, 2010 #5
    What would be the actual formula to calculate the stress on the cable, pulley, and Bracket?

    Not knowing the formula at this time, I am thinking that the stress is worse case at Horizontal and progressively gets lower as the center of gravity shifts downward toward the base, is it a correct assumption?

    The stainless steel cable is 3/16" and claims a strength upto 850 Lbs.
    I plan to get a stainless cable clamp that terminates the loop with screws and bolts, and I will see what the specifications are, per your suggestion. Want to make sure the terminations works properly.
     
  7. Oct 20, 2010 #6

    nvn

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    mar128a: Items 4 and 5 have now been added to post 4. See post 4.
     
    Last edited: Oct 20, 2010
  8. Oct 20, 2010 #7
    Per '5' Agreed, the tower is always secured in position to the bracket with 2 stainless steel U-Bolt clamps when in the vertical position. The advantage is that now the Tower will stay in position, while the the U-Bolt clamps are being attached, an additional safety measure.

    So based on the numbers, the worse case stress or pull will be the 137 Lbf or 611N, that I think will be well tolerated by three studs which are part of the exterior side of the house behind the siding to which the bracket plate is mounted to. In addition these same studs have angle steel which is also mounted to the rafters. The steel cable termination will include 3 sides of the tower itself, so no one side sees more stress than the other.

    Thank you for your help!
     
  9. Oct 20, 2010 #8
  10. Oct 22, 2010 #9

    nvn

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    mar128a: Not having analyzed that joint involving three studs (plus angle steel tied to rafters), I, like you, would guess it is adequate to withstand the 611 N lifting load.

    By the way, the cable maximum tensile force, which occurs when the tower is horizontal, is 322 N. This generates the 611 N force on the pulley at point B, mentioned in post 4. Do turn off the winch immediately as the tower reaches the vertical position. If you continue running the winch after the tower makes contact, you can generate a much higher loading on the system than the above lifting load.
     
  11. Oct 24, 2010 #10
    The winch will be a crank type not with electric motor since it is used rarely.
    I am thinking now of terminating the cable at the tower and putting a pulley at the holding bracket and another at the tower, so the winch will wind the steel cable from the pulley at the tower in a more esthetic way.
    My bigger concern now will the plasma welds at the main holding bracket if they can sustain the 611 Newton at the start of lift. I am thinking of adding aluminum angle bracket behind the main bracket, that will aid and lessen some of the strain the welds will see. This way if the welds begin to let go, there is a secondary back-up that will prevent the tower from crashing down.
     
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