Bob KQ2M wrote:
>> I assume that this ATC data is for estimated Windspeeds as
>> opposed to actual measured windspeeds? Do you happen to
>> know how often they update their data and ASCE 7-05 and
>> ASCE 7-93?
The windspeeds are only meaningful within the context of the
cited ASCE code version and have to be used with the equations
and procedures within that code version.
TIA-222-G uses ASCE 7-05 windspeeds along with certain "load
factors." Usually with towers the load combination 1.6W+1.2D
is controlling, where W is wind force and D is dead weight.
Most of the country is 90mph under 7-05/222-G; the tower's
strength is evaluated at 1.6 times the wind force at 90 mph
plus 1.2 times the tower's dead weight.
When TIA-222-H comes out I expect it to implement ASCE 7-10 or
7-16 with load factors of W+1.2D and W+0.9D. Most of the
country will be at 115 mph for a Category II structure. But
1.6 times the force at 90 mph is within 2% of 1.0 times the
force at 115 mph, so there's very little change in the
required design forces.
>> I also noticed that the windspeed data was IDENTICAL for my
>> qth at 810’ asl at the top of the hill facing a massive very
>> sharp dropoff to the West as compared to the end of my
>> street where the asl is ~ 350’ and sheltered by hills.
The basic wind speed is the same regardless of terrain. If your
QTH is on a hill, escarpment or ridge, then there is a "wind
speedup" multiplier that increases the expected force on the
tower. But you can't tell that from the ATC site as it only
provides the basic wind speed.
73 Jim K6OK
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