[TowerTalk] Wind 3 Second Gust Speeds

[Robert Chudek - KØRC]

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 at aol.com
Subject: [TowerTalk] Wind 3 Second Gust Speeds
To: towertalk at contesting.com
Message-ID: <551.80dc09b.3242d67e at 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