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[TowerTalk] FW: engineering help? Antenna weight for US Tower TX472

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Subject: [TowerTalk] FW: engineering help? Antenna weight for US Tower TX472
From: "Matt" <maflukey@gmail.com>
Date: Thu, 11 Jun 2015 23:27:56 -0500
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
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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