[450] K1FSY Mast Strength Analysis

Fri Nov 15 13:39:48 EST 2013

Awesome!

Quoting John Foege <john.foege at gmail.com>:

> I measured the pixel length of the mast and the pixel length of the section
> of mast past the thrust bearing from the pic you posted to the list the
> other night. It's 16.3 ft. of masting past the thrust bearing. Antenna is
> around 16' up from thrust bearing.
>
> UPDATED RESULT:
>
> Assuming everything from the original *.txt file but changing the masting
> to 1-1/2" trade size standard EMT conduit (1.74" OD / 0.065" wall
> thickness) the numbers are as follows:
>
> 16.3' ft of mast protruding from top of tower / thrust bearing and M2
> 2M9SSB mounted at 16' ft:
>
> Exceed yield strength, resulting in irreversible bending @ 60 mph (bending
> stress: 36,290 psi)
> Exceed absolute tensile strength, resulting in snapping @ 76 mph (bending
> stress: 58,225 psi)
>
> So, essentially you would need a Category 1 hurricane or a F0 tornado to
> hit your house to snap your mast.
>
> Methinks you shall be fine ;-)
>
>
> On Fri, Nov 15, 2013 at 12:23 PM, David McKenzie <k1fsy at vhfwiki.com> wrote:
>
>> think so
>>
>>
>> On Fri, Nov 15, 2013 at 12:18 PM, John Foege <john.foege at gmail.com> wrote:
>>
>>> 1.74" OD
>>> On Nov 15, 2013 12:18 PM, "John Foege" <john.foege at gmail.com> wrote:
>>>
>>>> Ok. I'll redo it for 1-1/2" EMT. The OD is 1.71 nominal I think. I have
>>>> a chart.
>>>>
>>>> Would you say 16' ft above thrust bearing and top of roof tower is
>>>> accurate?
>>>> On Nov 15, 2013 12:13 PM, "David McKenzie" <k1fsy at vhfwiki.com> wrote:
>>>>
>>>>> you did, it's 1 1/2" which is roughly 1 3/4"
>>>>>
>>>>>
>>>>> On Fri, Nov 15, 2013 at 5:06 AM, John Foege <john.foege at gmail.com>wrote:
>>>>>
>>>>>> If you are using 1-1/2" trade size EMT (1.74" OD) the numbers go up
>>>>>> *drastically* in what it can handle...so if I used the wrong EMT size,
>>>>>> please let me know.
>>>>>>
>>>>>> I hope you have found my work useful and interesting.
>>>>>>
>>>>>>
>>>>>> On Fri, Nov 15, 2013 at 5:04 AM, John Foege <john.foege at gmail.com>wrote:
>>>>>>
>>>>>>> December*
>>>>>>>
>>>>>>>
>>>>>>> On Fri, Nov 15, 2013 at 5:04 AM, John Foege  
>>>>>>> <john.foege at gmail.com>wrote:
>>>>>>>
>>>>>>>> It's very rare, afaik, that we, here inland, get wind gusts over
>>>>>>>> 50mph - however, in Decemeber it has be known to get up to  
>>>>>>>> 55+ mph gusts
>>>>>>>> once in a blue moon according to historical wind data I've  
>>>>>>>> been looking
>>>>>>>> through for Waterbury!!
>>>>>>>>
>>>>>>>>
>>>>>>>> On Fri, Nov 15, 2013 at 4:51 AM, John Foege  
>>>>>>>> <john.foege at gmail.com>wrote:
>>>>>>>>
>>>>>>>>> After eyeballing your pic "towering above" from earlier - I
>>>>>>>>> guesstimated that you've got 16' of 1-1/4 trade size EMT  
>>>>>>>>> above the thrust
>>>>>>>>> bearing, so making all the same assumptions from the earlier  
>>>>>>>>> analysis, here
>>>>>>>>> are your magic numbers:
>>>>>>>>>
>>>>>>>>> Exceed yield strength, resulting in irreversible bending @ 53 mph
>>>>>>>>> (bending stress: 35,767 psi)
>>>>>>>>> Exceed absolute tensile strength, resulting in snapping @ 67 mph
>>>>>>>>> (bending stress: 57,161 psi)
>>>>>>>>>
>>>>>>>>> Moral of the story? If we are going to get over 50 mph gusts, point
>>>>>>>>> your antenna into the wind - and you should be fine. It will  
>>>>>>>>> be a real show
>>>>>>>>> to watch from the outside though :-)
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On Fri, Nov 15, 2013 at 4:34 AM, John Foege  
>>>>>>>>> <john.foege at gmail.com>wrote:
>>>>>>>>>
>>>>>>>>>> Results below also attached as *.TXT file for better
>>>>>>>>>> formatting/readability.
>>>>>>>>>>
>>>>>>>>>> Analysis of Antenna Mast Strength
>>>>>>>>>> ----------------------------------
>>>>>>>>>>
>>>>>>>>>> Produced for: K1FSY
>>>>>>>>>> Performed by: W1QEX
>>>>>>>>>> Date: 11/15/2013
>>>>>>>>>>
>>>>>>>>>> All calculations assume:
>>>>>>>>>> * Single M2-9SSB antenna with 1.2 ft^2 cross sectional wind
>>>>>>>>>> loading area is at top of mast
>>>>>>>>>> * 1-1/4 Trade Size EMT (1.51 in. OD / 0.065 in. nominal wall
>>>>>>>>>> thickness)
>>>>>>>>>> * 36,000 PSI elastic yield strength / 58,000 absolute tensile
>>>>>>>>>> strength (standard EMT conduit)
>>>>>>>>>> * Antenna is broadsided into the wind for maximum wind contact
>>>>>>>>>> surface area
>>>>>>>>>> * All wind speeds are rounded to the nearest whole mph value
>>>>>>>>>> * Point of failure is at thrust bearing / top of tower and mast
>>>>>>>>>> interface
>>>>>>>>>>
>>>>>>>>>> Case #1
>>>>>>>>>> -------
>>>>>>>>>> * Mast protrudes 20' above thrust bearing
>>>>>>>>>>
>>>>>>>>>> Results:
>>>>>>>>>>
>>>>>>>>>> Bending stress of 35,908 psi occurs @ 45 mph wind speed. Wind
>>>>>>>>>> speeds in excess of
>>>>>>>>>> 45 mph will exceed the elastic yield strength of EMT conduit,
>>>>>>>>>> resulting in an irreversible
>>>>>>>>>> bending of the mast.
>>>>>>>>>>
>>>>>>>>>> Bending stress of 57,612 psi occurs @ 57 mph wind speed. Wind
>>>>>>>>>> speed in excess of 57 mph
>>>>>>>>>> will exceed the absolute tensile strength of EMT conduit,
>>>>>>>>>> resulting in breaking of the mast.
>>>>>>>>>>
>>>>>>>>>> Case #2
>>>>>>>>>> -------
>>>>>>>>>> * Mast protrudes 17' above thrust bearing
>>>>>>>>>>
>>>>>>>>>> Results:
>>>>>>>>>>
>>>>>>>>>> Bending stress of 36,194 psi occurs @ 51 mph wind speed. Wind
>>>>>>>>>> speeds in excess of
>>>>>>>>>> 51 mph will exceed the elastic yield strength of EMT conduit,
>>>>>>>>>> resulting in an irreversible
>>>>>>>>>> bending of the mast.
>>>>>>>>>>
>>>>>>>>>> Bending stress of 58,792 psi occurs @ 65 mph wind speed. Wind
>>>>>>>>>> speed in excess of 65 mph
>>>>>>>>>> will exceed the absolute tensile strength of EMT conduit,
>>>>>>>>>> resulting in breaking of the mast.
>>>>>>>>>>
>>>>>>>>>> Case #3
>>>>>>>>>> -------
>>>>>>>>>> * Mast protrudes 15' above thrust bearing
>>>>>>>>>>
>>>>>>>>>> Results:
>>>>>>>>>>
>>>>>>>>>> Bending stress of 36,369 psi occurs @ 56 mph wind speed. Wind
>>>>>>>>>> speeds in excess of
>>>>>>>>>> 56 mph will exceed the elastic yield strength of EMT conduit,
>>>>>>>>>> resulting in an irreversible
>>>>>>>>>> bending of the mast.
>>>>>>>>>>
>>>>>>>>>> Bending stress of 58,462 psi occurs @ 71 mph wind speed. Wind
>>>>>>>>>> speed in excess of 71 mph
>>>>>>>>>> will exceed the absolute tensile strength of EMT conduit,
>>>>>>>>>> resulting in breaking of the mast.
>>>>>>>>>>
>>>>>>>>>> Case #4
>>>>>>>>>> -------
>>>>>>>>>> * Mast protrudes 10' above thrust bearing
>>>>>>>>>>
>>>>>>>>>> Results:
>>>>>>>>>>
>>>>>>>>>> Bending stress of 36,125 psi occurs @ 74 mph wind speed. Wind
>>>>>>>>>> speeds in excess of
>>>>>>>>>> 74 mph will exceed the elastic yield strength of EMT conduit,
>>>>>>>>>> resulting in an irreversible
>>>>>>>>>> bending of the mast.
>>>>>>>>>>
>>>>>>>>>> Bending stress of 58,4291 psi occurs @ 94 mph wind speed. Wind
>>>>>>>>>> speed in excess of 94 mph
>>>>>>>>>> will exceed the absolute tensile strength of EMT conduit,
>>>>>>>>>> resulting in breaking of the mast.
>>>>>>>>>>
>>>>>>>>>>  73s de W1QEX
>>>>>>>>>> John
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
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>>>>>>
>>>>>>
>>>>>
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>

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