Thanks guys,
I got a note from Gary Smith at US Towers saying their
calculations come from UBC 97 code. Looking that up I
found the UBC 97 code refers to the 'fastest mile'
reference.
So... the TX-455 is rated at 12.3 sq ft @ 70mph
(fastest mile method) and the LM-354 is rated at 23 sq
ft @ 85mph (3 second gust speed method). I found a
paper describing the new 'tia-222-g' standard which
includes a conversion table from fastest mile method
to 3 second gust method
(http://www.mei1inc.com/NAB-2003presentation.pdf).
This conversion plus a conversion algorithm that
someone sent me says that 70mph 'fastest mile' is
equivalent to 85mph '3 second gust'.
So.... I'd say that in equivalent terms the lm-354 has
nearly twice the load rating as the tx-455. Whew....!
Hard to understand since the towers are the same
height and same weight. I have had a couple folks
mention that Tashjian had started using a higher
strength steel. I wonder if that could make such a
significant difference.
Thanks for everyone's input. I think I'm learning
something here!
Gary
--- K7LXC@aol.com wrote:
>
> In a message dated 1/26/2008 9:02:51 A.M. Pacific
> Standard Time,
> towertalk-request@contesting.com writes:
>
> > Looking at the specs for the Universal Towers
> TX-455
> versus the Tashijian LM-354 tower they are very
> similar. Same height, same weight, etc. However
> the
> LM-354 is rated at 23 sqft load at 85mph while the
> TX-455 is rated at only 12.3 sqft at 70mph.
>
> > I wonder if there is a good reason the LM-354 is
> rated
> higher or if it may be exagerating its limits?
>
>
> Boy, this is a good one. Before the TIA-222
> and other building codes
> were so prevalent, crank-ups used to be rated at 50
> MPH windspeeds. Nowadays
> it's not even a wind until it reaches 70 MPH - the
> lowest windspeed rating
> in the US. Very few, if any of them, could meet the
> 70 MPH spec.
>
> Both of those towers were originally
> designed by the same guy - Lou
> Tristao - so they are reasonably similar
> structures. The difference is that
> one has a #3 top section (the 354) and the other
> (the 455) has a #4 top
> section. Since the 455 is known to conform to
> current codes, I'd say that its
> capacity is realistic. And in that vein, I'd say
> that the 354 is incredibly
> generous in its capacity rating. I don't think I've
> ever seen ANY crank-up tower
> that could take 23 sq.ft. @ 85 MPH. Karl is a PE so
> I'm assuming he knows what
> he's talking about but I'm very skeptical.
>
> Cheers,
> Steve K7LXC
> TOWER TECH n-
> Professional tower services for hams
> Cell: 206-890-4188
>
>
>
> **************Biggest Grammy Award surprises of all
> time on AOL Music.
>
(http://music.aol.com/grammys/pictures/never-won-a-grammy?NCID=aolcmp003000000025
> 48)
>
Gary Slagel/N0SXX
Lakewood, CO
http://marina.fortunecity.com/sanpedro/351
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