[450] K1FSY Mast Strength Analysis

[David McKenzie]

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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