[450] K1FSY Mast Strength Analysis

[John Foege]

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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