Hi Doug,
The lifting cable stress analysis is found on page 7 of the link that
accompanied your message. The analysis shows the factors of safety in the
cable tension as 15.2, 6.1, and 9.74 for sections 5,6, & 7 respectively. In
response to your question, the "weak link" is the middle cable.
The payload assumptions stated at the top of page 7 are as follows:
Antenna: 200#
Antenna mount: 50#
Coax: 22#
Total payload: 272#
(rotor weight apparently is considered in one of the above)
Section weights are 188#, 221#, & 334# for sections 4,5,& 6 respectively.
Tensions for cables are calculated as follows:
T1 (top cable) = W4+Payload = 188+272=460#
T2 (middle cable) = (2 x T1) + W5 = (2 x 460) +221 = 1141#
T3 (each of 3 bottom cables) = ((3 x T1) + (2 x W5) + W6 ) / 3 = ((3 x 460)
+ (2 x 221) + 334) / 3 = 719#
All cables are listed as 1/4" 7x19 galvanized which has a rated break
strength of 7000#. The minimum recommended factor of safety for hoisting
applications is 5 to 1, so the maximum payload meeting the 5 to 1 minimum
safety factor is about 400#.
Hope this helps & good luck on your project!
73
Matt
KM5VI
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
kr2q@optimum.net
Sent: Thursday, June 11, 2015 12:08 PM
To: towertalk@contesting.com
Subject: [TowerTalk] engineering help? Antenna weight for US Tower TX472
Hi all,
http://www.ustower.com/wp-content/uploads/2014/05/TX-472.pdf
I am wondering about the spec for 200 pounds of antenna weight. Can someone
with some engineering background/experience please review the above link and
let me know:
1. Is there a "safety factor" on the 200 pounds? If so, what is it?
2. What point is the weak link for the 200 pounds?
RSVP
Thanks!!
de Doug KR2Q
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