[TowerTalk] RE: One Man Tower-LRFD

[kr7x at comcast.net]

Pete and List:

LRFD is a valid steel design code in the US, "Load Resistance Factor Design", and is allowable under all the building codes. It is sometimes called strength design method as opposed to Allowable Stress design which is the old stand by.

The wind load used in the design method, either LRFD or ASD, is determined by the particular code standard such as the UBC or BOCA or SBC or now the International Building Code. All of these allow the use of the TIA/EIA 222-F specifications for determining the wind load. The wind load and stresses are then evaluated using the particular steel design methodology (ASD or LRFD). This should not cause any problems with building officials especially if an PE prepares the documentation you submit (shameless plug).

What is important here for amateurs is what was the wind loading criteria used to determine the allowable areas. If the wind loading criteria is not a US Code recognized standard, then some conversion to a US code recognized standard may have to be determined. Wind velocity (speed) and allowable area are the critical factors for users.

Regards

Lonberg Design Group, Ltd.


Hank Lonberg, P.E.,S.E. / KR7X
President



> At 09:10 AM 2/18/04 -0500, Dudley Chapman wrote:
> >After seeing your message I found this.  What do people think about these
> >towers?
> >
> >http://www.onemantowers.com/
> 
> 
> I was perplexed by the windload numbers.  The site says:
> 
> 
> The wind speed ratings given below are from the engineer's certification 
> for the Mark 4 tower design. The report is for the 15-meter (49.7 ft) tower 
> and is expressed in the Load Range Factor Design (LRFD) standards used in 
> the U.S.A. The antenna is assumed to have a surface area of 19 square feet.
> 
> 
> Ratings are given for the antenna in its operating position at the top of 
> the tower and for the antenna in its lowest position.
> 
> 
> Terrain Category 2 (TC2) refers to open, relatively treeless terrain.
> Terrain Category 3 (TC3) refers to suburban and forested terrain.
> 
> 
> Antenna Up
> TC2: 103 mph (167kph)
> TC3: 120 mph (194 kph)
> 
> 
> Antenna Lowered
> TC2: 125 mph (202 kph)
> TC3: 148 mph (239 kph)
> 
> I've never heard of LRFD standards in the ham antenna context (or anywhere 
> else), and wonder how successful you would be in persuading your local 
> building permit office to accept these numbers in lieu of the EIA 
> standard-derived figures for 70mph, 90 mph and so on.  Looks like you might 
> be putting yourself in for some extra engineering costs.
> 
> No prices on the site either.  It would be interesting to see how they 
> compare with conventional crank-ups.
> 
> 
> 73, Pete N4ZR
> Check out the World HF Contest Station Database
> Updated 9 Jan 04
> www.pvrc.org/wcsd/wcsdsearch.htm
> 
> 
> 
> _______________________________________________
> 
> See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless Weather 
> Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any questions 
> and ask for Sherman, W2FLA.
> 
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