[450] K1FSY Mast Strength Analysis

[John Foege]

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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