[Antennas] WindDamage Statistics-FYI

Mon, 9 Sep 2002 17:34:48 EDT

The info is proprietary and appears in the FM Data Sheets, compiled by the 
largest insurer of high protected risk (HPR) properties worldwide, Factory 
Mutual. . Some libraries have a set of these data sheets which fill 5 or 6 
large three ring binders. 
Local building codes usually adopt and follow NFPA Standards, which often do 
not cover industrial conditions as well as FM standards, which were created 
specifically for this reason.
Winds are funny and hard to predict, as your experience proves. Usually, 
major ice buildup forms in still air during a prolonged mist or drizzle 
when ground air is near the freezing point. But at times these conditions 
can be closely followed by windy conditions though rarely high end winds. 
In my lifetime, in the northeast, Ive never seen any substantial wind 
associated with an ice storm, however geographical and topographical 
conditions create all kinds of different unique situations. Standards are 
always concensus vehicles that try to satisfy everyone. This is of course 
impossible. Hence conservative design is of value, especially when the value 
of that being protected is high.
I have not lived in an area especially prone to ice storms but have seen some 
doozies. Of course, over a long enough period, everything happens...eg the 
disastrous power outages in Quebec a few years ago due to a rare ice storm, 
estimated to be of 500 year interval. Or the Cat 5 hurricane that hit the 
Miami area. 
Most local codes use a minimum recommended wind design of 50 - 100 year 
frequency ( once every....) often due to a lack of better data. 
Bob