[TowerTalk] turnbuckle safety wires

Mon Sep 25 02:04:51 EDT 2017

Wind pressure on the tower varies as the square of the velocity. Going 
with the max velocity and looking at really tall towers is impressive, 
but why look at numbers from heights, or speeds "most" us will never 
experience? This was a 70 MPH area until a single derecho caused it to 
be bumped to 90, probably at the behest of the insurance companies. At 
this location I've never experienced gusts over 60 MPH in 33 years.  The 
pressure on a tower is not linear as wind speed tends to increase as you 
go up and that increase is not linear. My several thousand hours as 
pilot in command verifies that is a given.  Nearby objects can either 
lower, or increase the speed. They also create turbulence.  As we are 
almost surrounded by 70 - 80 ft trees, the wind speed at 40' here is far 
less than it was when I lived out on the farm which was flat land with 
very few trees.

Knowing the total forces on a tower is a straight forward summation. 
Unfortunately you need to know the wind speeds at the various heights as 
they all add up.  Calculus (the summation) can be replaced by 
calculating the force at various heights and adding the result at say 
every 10 feet.  Yes, it takes a bit of "relatively" simple math and even 
with the same math background as an engineer, I'd need to get the books 
out.  The wind area for the tower sections and the wind velocity at that 
height

As I'd been on the tower with winds at 30 - 40 MPH and it was too windy 
(well over 40) to go "up there" . The gusts were likely in, or close to 
60 MPH. So the scope observations were at well over 40 MPH.  I'm not 
finding fault with the modeling. I finding fault with applying max 
values to what most hams can expect.  We should be applying the 
realistic values for where we live. As for the difference in stretch, I 
used two guy anchor posts a little over 115 feet apart, a loos gauge, 
and a comealong.  I'll leave that for someone else to confirm as I do 
not have that much 6,000# Phillystran, nor can I afford to purchase it 
just for an experiment.

73, Roger (K8RI)

On 9/24/2017 Sunday 6:40 PM, Grant Saviers wrote:
> While I haven't built a tower FEA model and run my own Finite Element 
> Analysis to check Kurt's work, I've been through his work several 
> times and can't find fault.  Not surprising, since he is much more 
> qualified than I am as an ME.  I did have a good discussion with him 
> at the Visalia convention this year about his modeling assumptions and 
> inputs and that confirmed IMO that the modeling is well done.  It is 
> worth reading to understand why your experience at 30mph is different 
> than the math at max wind (I'll go with the math).
>
> I remember looking at the tall guyed broadcast towers east of I95 
> south of the Mass Pike when a hurricane was warming up.  The lean was 
> noticeable, maybe 10's of feet at the top.  Actually, there is DATA in 
> the NAB Engineers Handbook
>
> https://books.google.com/books?id=K9N1TVhf82YC&pg=PA1642&lpg=PA1642&dq=broadcast+tower+wind+sway&source=bl&ots=RtqdbP9_tu&sig=7FFsqw2hXl5vVgMYpM-qk5-TWig&hl=en&sa=X&ved=0ahUKEwjoj_eK7b7WAhXLr1QKHVBJBsMQ6AEIOTAD#v=onepage&q=broadcast%20tower%20wind%20sway&f=false 
>
>
> shows a table 6.8.3 for 1100' tower sway at 50 mph fastest mile of 
> 0.57deg.  100mph = 4x the force so maybe 2 degrees or 38' at the top.
>
> Grant KZ1W
>
> On 9/24/2017 14:15 PM, Roger (K8RI) on TT wrote:
>> I've been at the top of my 100' 45G when the wind became so strong I 
>> could no longer work (probably 30-40 MPH)  40 MPH will bounce you 
>> against the tower and difficult to breathe with the wind 90 degrees 
>> to face on.  There was definitely no slack on the downwind side, nor 
>> was there any sense of movement. Certainly the tension on the 
>> downwind side is reduced a bit, but it's a long way from being 
>> slack.  Whether EHS, or Phillystran the mechanics should prevent the 
>> downwind side from going slack.  My experience with the array 
>> http://www.rogerhalstead.com/ham_files/Tower29.htm Makes it difficult 
>> to accept the 15 to 18" deflection.  Maybe with a full size 40m Yagi, 
>> or 20m  long john
>>
>> With a telescope (lee side of the house, out of the wind) on a day 
>> too windy to climb the tower, I could barely detect movement of the 
>> tower top with the big array up there.
>> NOTE: scope and tripod weigh over 140#.  I need to get something 
>> lighter.  A 77 year old back and Arthritis means that scope and 
>> tripod have set in the shop for quite a few years. <:-(.
>>
>> 73, Roger (K8RI)
>>
>> On 9/24/2017 Sunday 1:25 PM, Grant Saviers wrote:
>>> My reference for noting that guys go slack is the K7NV FEA tower 
>>> study.  While Kurt doesn't note the stress in the downwind guys the 
>>> lean of the tower at the top is pretty convincing to me that they 
>>> slack.  For 100' tower the top moves 15 to 18" downwind for embedded 
>>> base and as much as 54" a for pier pin base.  While the wind loads 
>>> in the study are high, nothing fails in these models.
>>>
>>> For big commercial towers with very heavy guys/ft I have no opinion.
>>>
>>> http://k7nv.com/notebook/towerstudy/towerstudy1.html
>>>
>>> Grant KZ1W
>>>
>>> On 9/23/2017 22:59 PM, Roger (K8RI) on TT wrote:
>>>> It depends on the wire (size, length, composition, and the tension. 
>>>> I used to regularly climb a 200' commercial tower that had 1" wire 
>>>> rope for guys. there was an 18" tall, guy attachment point (don't 
>>>> remember the height) Those guys would ring like a tuning fork when 
>>>> struck with with a metal tool. it was way above 440
>>>> Hz.  That kind of vibration will unscrew a lot of hardware, but not 
>>>> with that kind of tension. The tower was a very solid 2' on a side 
>>>> in 20' sections, down onto an elevated pier pin base. The elevated 
>>>> base was a good 6' on a side. The pier pin was about 7' to 8' above 
>>>> ground. I have no idea as to how deep the concrete went.
>>>>
>>>> Turnbuckles on 1" guys are BIG!
>>>>
>>>> 73, Roger (K8RI)
>>>>
>>>> On 9/22/2017 Friday 8:04 PM, Steve Maki wrote:
>>>>> On 9/22/2017 19:36 PM, Grant Saviers wrote:
>>>>>> At the specified torque values for structural bolts, the fastener 
>>>>>> is far less likely to loosen. That isn't the static load in a 
>>>>>> turnbuckle which is exposed to many of the conditions that cause 
>>>>>> common fasteners to loosen.
>>>>>
>>>>> You would think so. But guy wires (and turnbuckles) seem to be 
>>>>> under a different dynamic situation than nuts and bolts in a motor 
>>>>> for example. Vibrations are relatively slow, and tension never 
>>>>> nears zero in a system with proper pre-tension. I think.
>>>>>
>>>>> -Steve K8LX
>>>>>
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>>
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> TowerTalk mailing list
>>>>> TowerTalk at contesting.com
>>>>> http://lists.contesting.com/mailman/listinfo/towertalk
>>>>
>>>>
>>>
>>> _______________________________________________
>>>
>>>
>>>
>>> _______________________________________________
>>> TowerTalk mailing list
>>> TowerTalk at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/towertalk
>>
>>
>

-- 

73

Roger (K8RI)

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus