The US Tower engineering report, while correct when published, isn't right
today and it's not right for your location.
* TIA-222-F is an out of date standard. TIA-222-G, which replaced
TIA-222-F, uses different equations and analytical methods. The two
standards really aren't comparable or compatible with each other.
* The wind speed is wrong. It has 85 mph, but in your area 222-G requires
90 mph. That might not seem like much but it represents a 12% increase in
design wind loads.
* The report says no ice but 222-G requires an assumed ice thickness of
0.75 inch in your part of NC.
Ice is a big deal and on that alone your hunch is probably right, this
report is likely optimistic. UST or another civil engineer needs to
reanalyze the tower to today's standards to determine the true tower
capacity for your location.
There is a strategy to increase the tower capacity under code, however:
Have the tower analyzed for the 90 mph standard while retracted and again
at perhaps 50 mph when extended. This will yield a much higher tower
capacity but it is contingent upon you always lowering your tower ahead of
big storms (which most people do anyway). I've used this method to help
local hams get permits for legacy crankup towers that don't meet 222-G when
extended. So far the local governments I've worked with have all accepted
this design approach. In some of the hurricane zones the "meets 222-G when
cranked down" analysis may be the only approach that works.
73 Jim K6OK
Wilson W4BOH wrote:
>>>There’s a local opportunity to get a TX-489 at a good deal.
This tower looks “nice”, but the spec’s seem pretty optimistic to me.<<<
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