Thank Lou and to all that have commented. All great advice and or real
life experiences.
Your input has help me greatly. WHAT A GROUP ('S)....
73 de
Ron W4LDE
w0fk_lou wrote:
>
>
> With all due respect to the telescoping tower manufacturers,
> advertising the wind loading strength of towers at 50 mph is simply
> marketing. If you are in a jurisdiction (city or county) that requires
> that building permits be obtained for antenna support structures
> (towers), or otherwise conform to Code requirements, 50 mph does not
> cut it.
>
> Tower engineering standards have evolved considerably over the last 10
> years or so, perhaps because of the mushrooming of cell towers.
> Current structural requirements that are being adopted thoughtout the
> US (from what I've seen) are based on the ANSI/EIA/TIA 222 standard,
> either Rev F (older) or G (newer). Wind load analysis under 222 varies
> based on where you're located in the US and which version of the
> standard is in effect in the permitting jurisdiction, but the lowest
> wind speed is 70 mph fastest mile (Rev F) or 90 mph (3 second gust,
> which roughly calculates to the 70 mph fastest mile standard).
>
> See http://www.mei1inc.com/NAB-2003presentation.pdf
> <http://www.mei1inc.com/NAB-2003presentation.pdf> for some technical
> details and the adopted standard maps (ice loading may also be a
> consideration). Another good read is on K7NV's web site,
> http://k7nv.com/notebook/topics/windload.html.
> <http://k7nv.com/notebook/topics/windload.html.>
>
> US Tower's older published ratings were based on an analysis under the
> Uniform Building Code in place in much of California in the 1990's,
> and that has for the most part been replaced by the International
> Building Code (which adopts the 222 standard for towers). Although
> their ratings may come somewhat close to the older UBC ratings, US
> Tower, as it should, is now taking into account the shape of the
> antenna elements in analyzing tower strength. An antenna with flat
> elements will have a greater wind load than one with round elements,
> and require greater structural strength. Consider that SteppIR
> antennas have a bit of both.
>
> If you're lucky and don't have to get a building permit where a
> structural engineer has to seal your plans and certify that the
> proposed structure will meet Code requirements, then the technical
> compliance isn't that big a deal. But you still need to pay attention
> to wind loading requirements from both a safety and risk avoidance
> perspective (i.e., will it fail and your investment lost?).
>
> Best advice I can offer in all circumstances is to get the strongest
> tower you can afford and keep it cranked down when not in use.
>
> Disclaimer: I am not an engineer, just a ham that's had to try and
> learn a lot about this subject.
>
> Lou, W0FK
>
> --- In SteppIR@yahoogroups.com <mailto:SteppIR%40yahoogroups.com>,
> w4lde <w4lde@...> wrote:
> >
> > I was getting ready to order the US Tower MARB-550 55ft tubular tower
> > and first decided to look once again at the US Tower WEB site for
> ratings.
> >
> > US Tower has updated there web site and now has new HAM tower
> > brochures. The Tubular towers (550) now only show a 10sq' rating based
> > on 50MPH.
> >
> > My plan is to mount a SteppIR 3-element with the 30/40 meter kit which
> > runs about 8 sq'. I am in a 70MPH zone.
> >
> > I check out several catalogs online one being Texas Towers and they
> > still show that same 9 sq' rating at 70mph and 22sq' at 50mph.
> >
> > The base is poured but so be it if I have to change.
> >
> > I am getting up in years and my climbing days are over, I was also
> > planning on the tilt over accessory from US Tower.
> >
> > I have looked at the Aluma tower crank up and with guys is rated at
> > 80mph at 25sq ft. Its also available with a tilt over base.
> >
> > If there was a way to guy the MARB I would feel much safer? To go with
> > the Aluma is a 40% add but maybe worth the money in the long run.
> >
> > If a tilt over assembly was available through US Tower for the TX or
> > the HXD series then I would go that route. Not shown on web site. Also
> > the TX and HXD are now rated at 50mph but I would have enough safety
> > margin with either at 70mph.
> >
> > Need to get on with it before the next solar cycle comes and goes hi
> > hi. Any advice or comments are welcomed.
> >
> > 73 de
> > Ron W4LDE
> >
>
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