For the setup you have given:
Max lifting cable tension = (M1 x T) + (M2 x A)
Where:
T = gross tower weight
A = top payload weight
M1 = ratio of moment arm from tower mass to lifting point / SINE min cable
angle. For your case the minimum cable angle of 45 deg occurs with the tower
horizontal and M1 = 32/(13 x SIN(45)) = 3.5
M2 = ratio of moment arm from tower payload to lifting point / SINE min
cable angle. For your case M2 = (64/(13 x SIN(45) = 7.0
Assumptions:
1. the elevation of the hinge centerline at the tower base does not exceed
top of tower elevation at any time (min lift angle is 45 deg)
2. tower center of gravity is at or below the middle of the tower (upper
section tower weight does not exceed lower section weight)
3. all payload is at the 64 ft level (no mast extension)
4. lifting cable attachment and lifting cable support are both at the 13 ft
level
Be aware that the horizontal and vertical loads from the cable tension
transferred to the attachment point are subject to the cable angle and they
change as you perform the lift.
If the lifting attachment point is on your house - the load is a point load
and not a distributed load.
Beware that your house/roof framing is not likely designed for large point
loads, particularly with respect to strength of lateral bracing - don't pull
your roof down AND drop your tower in the process.
Good luck with your project.
Matt
KM5VI
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Ray,
W4BYG
Sent: Tuesday, September 17, 2013 10:21 AM
To: TowerTalk@contesting.com
Subject: [TowerTalk] Help with calculations...
I have a 64' aluminum 14"/18" tower with a steel hinged base. I have
previously raised and lowered it several times with 16' ground mounted, back
guyed gin pole and HD block and tackle, pulled by my car. This was done
successfully by intuitive estimation of the loads, plus a large safety
margin factor.
However, I am in a different qth and installation scenario (now 75 years
young) . I would like to be able to raise the tower with beam/feedline
installed while on the ground with a tilt hinge mount, and then temporarily
anchored to my roof line (with appropriate inside bracing), for raising. I
can calculate the tower alone loads, but I'm not sure about the added load
of the beam at the end or top. Thus, I would like to more accurately
calculate the estimated loads on the tackle/hardware to the roof.
My question: Is there a formula(s) in which I can enter the linear tower
weight as well as well as the beam weight at the top, then the attachment
location, to estimate or determine what the rigging loads would be at the 13
' level of the tower and the 13' height at the roof line? This would assist
me in determining the needed attachments and bracing for the hardware to
the roof rafters. I am estimating it will be about 1200 lbs or so, but I
would like to be more sure.
I was not able to find anything online that I could decipher and apply.
Any assistance will be appreciated.
Ray, W4BYG
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