HI Larry,
It's a good idea to go find the local radio club and get acquainted with
some of the 'old timers'. Time to listen to their camp fire stories about
ham antennas, towers, etc.
>From the US Tower manufacturer WEB Site for ham crank-up towers:
Windloading ratings based upon IBC 2006 (TIA/EIA-222-F) at 76mph and 90mph
3-second gusts:
HDX-538: 26.6 sq. ft.
HDX-555: 23.4 sq. ft.
HDX-572: 14.1 sq. ft.
HDX-589: 9.2 sq. ft.
HDX-5106: 1.0 sq. ft. at 90mph
So, the height you leave the antenna cranked up when you spend your summer
up north is really determined by a couple of things:
- Are you BRAIN DEAD? If so, then leave it cranked up to 72ft *
- Are you DIM? If so, then leave it cranked up to 62ft *
- Are you a RISK TAKER? If so, then leave it cranked up to 52ft *
Are you aware of the following information (below)?
More storms hit Florida than any other US state. Looking at the years from
1851 to 2004, for hurricanes of Category 3 and higher: Florida had 35
hurricanes; Texas, 19; Georgia, 3; Alabama, 6. (From the National Hurricane
Center).
Typically, at least one named storm makes landfall in Florida every season.
Some areas of Florida may be as risky as the Caribbean islands. The chances
of Miami being hit by a hurricane is "higher than anywhere in the Caribbean"
(--see article at About.com's Caribbean Travel website.) The period from
August to October is the height of the hurricane season in Florida.
Remember, though, that Mother Nature isn't reading any calendars.
For Floridians, hurricane preparedness is part of life. For example, read
the Hurricane Survival Guide at the Orlando Sentinel newspaper site.
Some Years are Worse than Others
2004, for instance, was a big year for Florida hurricanes: Charley, Frances,
Ivan and Jeanne hit the Florida coast, causing over 20 deaths plus more than
$40 billion in damage. 2007, meanwhile, saw three tornadoes sweep across
central Florida with several fatalities.
* Category One Hurricane:
Sustained winds 74-95 mph (64-82 kt or 119-153 km/hr). Damaging winds are
expected. Some damage to building structures could occur, primarily to
unanchored structures (such as school portables). Some damage is likely to
poorly constructed signs. Loose outdoor items will become projectiles,
causing additional damage. Persons struck by windborne debris risk injury
and possible death. Numerous large branches of healthy trees will snap. Some
trees will be uprooted, especially where the ground is saturated. Many areas
will experience power outages with some downed power poles.
<http://weather.gov/cphc/summaries/1982.php#Iwa> Hurricane Iwa (passing just
northwest of Kauai in 1982) and
<http://weather.gov/cphc/summaries/1959.php#Dot> Hurricane Dot (landfall on
Kauai in 1959) are examples of Category One hurricanes that directly
impacted Hawaii.
* Category Two Hurricane:
Sustained winds 96-110 mph (83-95 kt or 154-177 km/hr). Very strong winds
will produce widespread damage. Some roofing material, door, and window
damage of buildings will occur. Considerable damage to unanchored structures
and poorly constructed signs is likely. A number of glass windows in high
rise buildings will be dislodged and become airborne. Loose outdoor items
will become projectiles, causing additional damage. Persons struck by
windborne debris risk injury and possible death. Numerous large branches
will break. Many trees will be uprooted or snapped. Extensive damage to
power lines and poles will likely result in widespread power outages that
could last a few to several days. There is no record of a Category Two
hurricane directly impacting Hawaii. Elsewhere in the United States,
<http://www.nhc.noaa.gov/1995erin.html> Hurricane Erin (1995, 100 mph at
landfall in northwest Florida) and
<http://www.nhc.noaa.gov/2003isabel.shtml> Hurricane Isabel (2003, 105 mph
at landfall in North Carolina) are examples of Category Two hurricanes at
landfall.
* Category Three Hurricane:
Sustained winds 111-129 mph (96-112 kt or 178-208 km/hr). Dangerous winds
will cause extensive damage. Some structural damage to houses and buildings
will occur with a minor amount of wall failures. Unanchored structures and
poorly constructed signs are destroyed. Many windows in high rise buildings
will be dislodged and become airborne. Persons struck by windborne debris
risk injury and possible death. Many trees will be snapped or uprooted and
block numerous roads. Near total power loss is expected with outages that
could last from several days to weeks. There is no record of a Category
Three hurricane directly impacting Hawaii. Elsewhere in the United States,
<http://www.nhc.noaa.gov/pdf/TCR-AL182005_Rita.pdf> Hurricane Rita (pdf)
(2005, 115 mph landfall in east Texas/Louisiana) and
<http://www.nhc.noaa.gov/2004jeanne.shtml> Hurricane Jeanne (2004, 120 mph
landfall in southeast Florida) are examples of Category Three hurricanes at
landfall.
* Category Four Hurricane:
Sustained winds 130-156 mph (113-136 kt or 209-251 km/hr). Extremely
dangerous winds causing devastating damage are expected. Some wall failures
with some complete roof structure failures on houses will occur. All signs
are blown down. Complete destruction of unanchored structures. Extensive
damage to doors and windows is likely. Numerous windows in high rise
buildings will be dislodged and become airborne. Windborne debris will cause
extensive damage and persons struck by the wind-blown debris will be injured
or killed. Most trees will be snapped or uprooted. Fallen trees could cut
off residential areas for days to weeks. Electricity will be unavailable for
weeks after the hurricane passes.
<http://weather.gov/cphc/summaries/1992.php#iniki> Hurricane Iniki, which
made landfall on Kauai in 1992, is an example of a Category Four hurricane
at landfall in Hawaii.
* Category Five Hurricane:
Sustained winds greater than 157 mph (137 kt or 252 km/hr). Catastrophic
damage is expected. Complete roof failure on many residences and industrial
buildings will occur. Some complete building failures with small buildings
blown over or away are likely. All signs blown down. Complete destruction of
unanchored structures. Severe and extensive window and door damage will
occur. Nearly all windows in high rise buildings will be dislodged and
become airborne. Severe injury or death is likely for persons struck by
wind-blown debris. Nearly all trees will be snapped or uprooted and power
poles downed. Fallen trees and power poles will isolate residential areas.
Power outages will last for weeks to possibly months. There is no record of
a Category Five hurricane directly impacting Hawaii. Elsewhere in the
United States, <http://www.nhc.noaa.gov/pdf/TCR-1969Camille.pdf> Hurricane
Camille (pdf) (1969, 190 mph at landfall in Mississippi) and
<http://www.nhc.noaa.gov/1992andrew.html> Hurricane Andrew (1992, 165 mph at
landfall in Southeast Florida) are examples of Category Five hurricanes at
landfall
UR kidding right? Dude you live on the west coast of FL. Hurrican
land...if you aren't there and you want a tower when you return you better
leave it cranked down all the way. The lowest of the hurricane categories,
the type one, puts your tower at risk if cranked up. even a tropical storm
would place it at risk.
Leave it cranked down is my best advice or start putting your lunch money
change in a bucket so you can replace the tower when it bends over.
Good Luck and Have Fun Operating via the Internet,
Dave
Wa3gin
Internet Remote since 2000
* * seems like the wind load is not relevant question; at any height
above40ft the risk of tower failure increase dramatically during an average
tropical storm or hurricane (IMHO). Now find an antenna that will survive
90mph or greater gust ;-)
*
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Larry Loen
Sent: Monday, June 25, 2012 3:48 PM
To: towertalk@contesting.com
Subject: [TowerTalk] Windload Planning for Towers
What wind load should I actually plan for?
Officially, it seems like the world is migrating to a 90 MPH
(momentary) standard. That leaves me at 11 square feet in my
location. But, the advertizing (at more like 50 MPH) suggests I can
go up to 30 square feet without fuss with my HDX 572. Of course, they
are taking no risks in stating something like that.
Keep in mind that this is probably the only time in my life I'll have
the money to put up a tower like this. So, I'm not interested in a
design point that says I wasn't aggressive enough if it doesn't blow
down someday.
I want this thing to be standing 30 years from now, but I don't want
to have the thing at 25 feet all its life either.
I will eventually be operating remotely, so what I need to do in my
case is plan to erect the thing and largely leave it there at whatever
height (and antenna array) I deploy. So, I need to plan on 64 to 72
feet of height here, depending on some of my choices.
What do people on this reflector actually plan for and why?
Larry Wo0Z
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