Al,
For those following along, here's a link to an overview of the new TIA-222-G
standard: http://beradio.com/mag/radio_changes_tower_standards/index.html It
contains good background material and how and why the criteria has changed in
the updated standard.
Here's a link to a PDF file of the new TIA-222-G specification:
http://www.mei1inc.com/NAB-2003presentation.pdf This is a presentation of the
proposed changes, prior to final approval. I doubt there has been any
significant change. Or you can purchase the final 15-chapter standard for $361
in either hardcover or electronic form!
On the "freebie" I mentioned above, page 5 of 7 has the conversion chart Al was
referring to. It shows the 90 mph speed is a 3 second gust, which = a 75 mph
fastest-mile, which = 62 mph 10-minute average, which = 60 mph hourly mean. So
the answer to Al's question is yes, 90 mph is the 3-second gust speed.
Page 3 of 7 shows the ice loading map. It appears some leniency has been
granted here in that the Twin Cities looks to be in the 3/4" radial icing zone.
Back to the bottom of page 5 of 7, there appears to be some wiggle room in
determining whether Al's location might fall within Exposure B, C, or D.
A strong argument could be made to move from Exposure C (the default) to
Exposure B if you live in an area buffered by trees, especially if this is a
thick cover for a quarter-mile in all directions. I'm looking for additional
information regarding the impact to wind velocities near the ground.
Keep in mind the TIA-222-G is written to cover ALL antenna structures,
including the three 1500 foot monsters in Shoreview, MN. This new specification
is going to impact many tower owners, as you will read in this article:
http://electronics.ihs.com/news/newsletters/tele-nov05-1.htm
I believe, after investigating this new standard, any ham contemplating a new
tower installation where the city engineering department has adopted this new
standard is going to have a much safer installation!
73 de Bob - KØRC in MN
Message: 5
Date: Wed, 20 Sep 2006 13:38:06 EDT
From: Aldewey@aol.com
Subject: [TowerTalk] Wind 3 Second Gust Speeds
To: towertalk@contesting.com
Message-ID: <551.80dc09b.3242d67e@aol.com>
Content-Type: text/plain; charset="US-ASCII"
All;
I am sure this has been discussed before but I am a newbie to the TowerTalk
reflector.
In applying for a building permit with my city, they told me "it needs to be
rated for 90 MPH with 1/2 inch radial ice". I asked him what standard he was
referring to and he referred me to the latest IBC Section 3108.4. This spec ,
in turn, refers to EIA/TIA 222-E. EIA/TIA 222 g has a windload map that that
, indeed, confirms the 90 mph requirement. However, if I am reading it
correctly, it is referring to 3 second gust speed. It, in turn, includes a
table
for converting 3 second gust speed to "Fastest-Mile (MPH) Speed. The chart
indicates that 90 mph (3 second gust) corresponds to 75 MPH "fastest-MPH speed".
Setting aside for a minute the radial ice issue, does this mean that that the
70 MPH rating I get from a tower manufacturer like US Tower really
corresponds the higher 3 second gust speed rating as required by the
specification.
Or is this just wishful thinking?
Al, K0AD
Plymouth, MN
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