[450] K1FSY Mast Strength Analysis

[John Foege]

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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