[450] K1FSY Mast Strength Analysis

Fri Nov 15 13:27:56 EST 2013

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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