<p>1.74" OD</p>
<div class="gmail_quote">On Nov 15, 2013 12:18 PM, "John Foege" <<a href="mailto:john.foege@gmail.com">john.foege@gmail.com</a>> wrote:<br type="attribution"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<p>Ok. I'll redo it for 1-1/2" EMT. The OD is 1.71 nominal I think. I have a chart.</p>
<p>Would you say 16' ft above thrust bearing and top of roof tower is accurate?</p>
<div class="gmail_quote">On Nov 15, 2013 12:13 PM, "David McKenzie" <<a href="mailto:k1fsy@vhfwiki.com" target="_blank">k1fsy@vhfwiki.com</a>> wrote:<br type="attribution"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">you did, it's 1 1/2" which is roughly 1 3/4"<br></div><div class="gmail_extra"><br><br><div class="gmail_quote">On Fri, Nov 15, 2013 at 5:06 AM, John Foege <span dir="ltr"><<a href="mailto:john.foege@gmail.com" target="_blank">john.foege@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">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. <br>
<br>I hope you have found my work useful and interesting.<br>
</div><div class="gmail_extra"><br><br><div class="gmail_quote">On Fri, Nov 15, 2013 at 5:04 AM, John Foege <span dir="ltr"><<a href="mailto:john.foege@gmail.com" target="_blank">john.foege@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">December*<br></div><div><div><div><div><div class="gmail_extra"><br><br><div class="gmail_quote">
On Fri, Nov 15, 2013 at 5:04 AM, John Foege <span dir="ltr"><<a href="mailto:john.foege@gmail.com" target="_blank">john.foege@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">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!!<br>
</div><div><div><div class="gmail_extra"><br><br><div class="gmail_quote">On Fri, Nov 15, 2013 at 4:51 AM, John Foege <span dir="ltr"><<a href="mailto:john.foege@gmail.com" target="_blank">john.foege@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div><div><div>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:<br>
<br></div>Exceed yield strength, resulting in irreversible bending @ 53 mph (bending stress: 35,767 psi)<br></div>Exceed absolute tensile strength, resulting in snapping @ 67 mph (bending stress: 57,161 psi)<br><br></div>
<div>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 :-)<br></div><div><div><div><div><br></div>
</div></div></div></div><div><div><div class="gmail_extra"><br><br><div class="gmail_quote">On Fri, Nov 15, 2013 at 4:34 AM, John Foege <span dir="ltr"><<a href="mailto:john.foege@gmail.com" target="_blank">john.foege@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div>Results below also attached as *.TXT file for better formatting/readability.<br></div><div><br>Analysis of Antenna Mast Strength<br>
----------------------------------<br><br>Produced for: K1FSY<br>Performed by: W1QEX<br>
Date: 11/15/2013<br><br>All calculations assume:<br>* Single M2-9SSB antenna with 1.2 ft^2 cross sectional wind loading area is at top of mast<br>* 1-1/4 Trade Size EMT (1.51 in. OD / 0.065 in. nominal wall thickness)<br>
* 36,000 PSI elastic yield strength / 58,000 absolute tensile strength (standard EMT conduit)<br>* Antenna is broadsided into the wind for maximum wind contact surface area<br>* All wind speeds are rounded to the nearest whole mph value<br>
* Point of failure is at thrust bearing / top of tower and mast interface<br><br>Case #1 <br>-------<br>* Mast protrudes 20' above thrust bearing<br><br>Results:<br><br>Bending stress of 35,908 psi occurs @ 45 mph wind speed. Wind speeds in excess of <br>
45 mph will exceed the elastic yield strength of EMT conduit, resulting in an irreversible <br>bending of the mast.<br><br>Bending stress of 57,612 psi occurs @ 57 mph wind speed. Wind speed in excess of 57 mph<br>will exceed the absolute tensile strength of EMT conduit, resulting in breaking of the mast.<br>
<br>Case #2 <br>-------<br>* Mast protrudes 17' above thrust bearing<br><br>Results:<br><br>Bending stress of 36,194 psi occurs @ 51 mph wind speed. Wind speeds in excess of <br>51 mph will exceed the elastic yield strength of EMT conduit, resulting in an irreversible <br>
bending of the mast.<br><br>Bending stress of 58,792 psi occurs @ 65 mph wind speed. Wind speed in excess of 65 mph<br>will exceed the absolute tensile strength of EMT conduit, resulting in breaking of the mast.<br><br>Case #3 <br>
-------<br>* Mast protrudes 15' above thrust bearing<br><br>Results:<br><br>Bending stress of 36,369 psi occurs @ 56 mph wind speed. Wind speeds in excess of <br>56 mph will exceed the elastic yield strength of EMT conduit, resulting in an irreversible <br>
bending of the mast.<br><br>Bending stress of 58,462 psi occurs @ 71 mph wind speed. Wind speed in excess of 71 mph<br>will exceed the absolute tensile strength of EMT conduit, resulting in breaking of the mast.<br><br>Case #4 <br>
-------<br>* Mast protrudes 10' above thrust bearing<br><br>Results:<br><br>Bending stress of 36,125 psi occurs @ 74 mph wind speed. Wind speeds in excess of <br>74 mph will exceed the elastic yield strength of EMT conduit, resulting in an irreversible <br>
bending of the mast.<br><br>Bending stress of 58,4291 psi occurs @ 94 mph wind speed. Wind speed in excess of 94 mph<br>will exceed the absolute tensile strength of EMT conduit, resulting in breaking of the mast.<br><br>
</div>
<div>73s de W1QEX<span><font color="#888888"><br></font></span></div><span><font color="#888888"><div>John<br></div><div><br></div></font></span></div>
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