[450] K1FSY Mast Strength Analysis

[David McKenzie]

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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