> If people are using spreadsheets, how come we don't have a
> spreadsheet that has "close enough" analysis for bending
> moments typical crankup tower sections can resist?
Derivation of the tower equations as a function of telescoping tower height
can be found in the July/Aug 2001 Issue of QEX Communications Quarterly.
There is a spreadsheet available from ARRL that covers this case. There is a
revision to the spreadsheet as well so you should look for that too.
That spreadsheet program will provide you "close enough" estimates so you
can answer all the questions you pose in your email.
You will need to read carefully so that you understand how things work. This
spreadsheet and article are what I used when selecting an HDX-572 tower,
mast, bearing, rotator, Force 12 C31-XR and Cushcraft XM-240 which would
meet the IBC-2006 specification required in Idaho. The stress analysis
calculations covering that tower were made available by US Tower. The US
Tower work, done by and wet stamped by professional engineers, gave
essentially identical results as I obtained using the QEX spreadsheet.
The Spreadsheet is NOT a substitute for a professional engineer review and
sign off. I got that as well. I sleep very well at night unless the wind is
blowing at an "hourly AVERAGE" velocity of 75 mph and my tower is fully
extended. [The 3 second gust for that average speed is more than 100 mph].
Idaho is windy but almost never that windy.
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