[TowerTalk] ridge top derating factors

[Tower2sell@aol.com]

The ASCE 7-88 wind map is not in EIA-222-F, 1996. What they did was to make a county wind speed chart using the ASCE 7-88 wind map. It lists all the counties and their minimum wind speed. They are both fastest mile wind speeds.

The NEW version of ASCE 7-95 has a new wind map with 90 mph minimum wind speed and is a 3 second "gusted" wind. These winds will be incorporated into the NEW EIA-222-G when it comes out

I hope this helps.

Tower2sell@aol.com




In a message dated Thu, 13 Apr 2000 11:59:12 AM Eastern Daylight Time, "Curtis, David B" <david.b.curtis@intel.com> writes:



> 
> Hmmm... so what is an ASCE 7-88 wind map? Is it part of TIA/EIA-222-F,or is
> it yet another document? But I take from your comment that the map doesn't
> say anything other than "go ask".
> 
> 73, Dave N6NZ
> 
> -----Original Message-----
> From: K7LXC@aol.com [mailto:K7LXC@aol.com]
> Sent: Thursday, April 13, 2000 8:48 AM
> To: david.b.curtis@intel.com; towertalk@contesting.com
> Subject: Re: [TowerTalk] ridge top derating factors
> 
> 
> In a message dated 04/12/2000 1:15:07 PM Pacific Daylight Time, 
> david.b.curtis@intel.com writes:
> 
> > EIA-222-F lists Mariposa county California as an 85 mph county, 85 is
> lowest
> >  possible.
> >  
> >  But... I have a ridge-top location. Therefore, I need to derate for wind
> >  acceleration over the ridge. I've read Leeson's book and done some other
> >  research, but it is not straight forward and I couldn't convince myself 
> that
> >  I know how to calculate the correct derating factor. So, my question to
> the
> >  group: How can I arrive at the right derating factor?
> 
>       There is a note on many county windspeeds in the TIA-222 that states 
> "Site may be within a special wind region indicated on ASCE 7-88 wind map. 
> Check with local authorities before specifying basic wind speed". You might 
> check with your local building department and see if this applies to your 
> situation. 
> 
>      Exposed ridges are particularly exposed not only to direct horizontal 
> winds but also venturi winds coming UP the side of the hill and hitting the 
> antennas from underneath. This is where you'll need 120 degree trusses on 
> your antenna booms to keep them from breaking.
> 
> Cheers,    Steve    K7LXC
> Tower Tech 
> 
> 
> --
> FAQ on WWW:               http://www.contesting.com/towertalkfaq.html
> Submissions:              towertalk@contesting.com
> Administrative requests:  towertalk-REQUEST@contesting.com
> Problems:                 owner-towertalk@contesting.com
> Search:                   http://www.contesting.com/km9p/search.htm



--
FAQ on WWW:               http://www.contesting.com/towertalkfaq.html
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm