[450] K1FSY Mast Strength Analysis

[John Foege]

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
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.vhfwiki.com/pipermail/450/attachments/20131115/a3ba7633/attachment.html>
-------------- next part --------------
_______________________________________________
450 mailing list
450 at lists.vhfwiki.com
http://lists.vhfwiki.com/cgi-bin/mailman/listinfo/450