At 09:00 AM 7/12/2005, Michael Keane K1MK wrote:
>On Mon, 11 Jul 2005 at 00:37:06 <isp@bnjcomp.com> wrote:
>
> > So I can compare where do I find what "normal" or
> > "average" soil conditons means?
>
>One would expect to be able to find something about the assumed soil
>conditions somewhere in the drawing notes, typically in the notes to the
>foundation drawing(s).
>
>Normal soil usually has a specific, technical meaning. One will commonly
>see a drawing note such as: "Foundations designed in accordance with
>ANSI/TIA/EIA normal soil" or other words to that effect.
>
>EIA-222-F defines normal soil as:
>
>"A cohesive soil with an allowable net vertical bearing capacity of 4000
>pounds per square foot and an allowable net horizontal pressure of 400
>pounds per square foot per lineal foot of depth to a maximum of 4000
>pounds per square foot."
>
>Be warned though, the "normal" soil defined in EIA-222 is just a set of
>parameters intended for bidding purposes so quotes can be prepared and
>compared on a common basis when the customer does not provide a
>geotechnical report as part of an RFQ.
>
>EIA-222 calls it normal soil but the mechanical properties are not the
>properties of an average soil; some properties of "normal" soil are quite
>atypical.
>
>
>And don't assume that the standard foundation design has been
>substantially over-engineered in order to cover all or most cases. The
>foundation design for normal soil is used as a quoting standard. A
>manufacturer is not going to deliberately place itself at a competitive
>disadvantage by designing a foundation that requires more cubic yards of
>concrete than what's needed to achieve the safety factors specified in the
>EIA-222 standard.
>
>73,
>Mike K1MK
Mike hits the nail exactly on the head. The mfr drawing is designed to
provide a common basis for comparison. The going in assumption is that it
will be reviewed by a competent person before using it blindly, just like
any other engineered component. Kind of like bolts. The fact that the bolt
is graded and certified at a particular level doesn't mean it works for all
bolt applications. The user is expected to use judgement on whether they
need a grade X bolt for their particular need.
That competent review doesn't necessarily have to be a licensed engineer.
It's all about risk acceptance posture: If you're putting up a tower down
on the lower 40 and the only thing around for 2 miles is sheep or cows, the
standard of review is substantially different than if you're putting up
that tower on a 5000 square foot lot in a crowded subdivision.
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Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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