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RE: Pole Foundations

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Neil,

Agreed, sir.

SYED FAIZ AHMAD; MENGG, MASCE
SENIOR STRUCTURAL ENGINEER
SAUDI OGER LTD
RIYADH, SAUDI ARABIA.



From: Neil Moore <nmoore(--nospam--at)innercite.com>
Reply-To: <seaint(--nospam--at)seaint.org>
To: <seaint(--nospam--at)seaint.org>
Subject: RE: Pole Foundations
Date: Sun, 09 Dec 2001 19:27:46 -0800

Syed:

We haven't done "handwritten" calcs for years.  In actuality, if you are
doing a foundation for a pole, the very first thing you need is a soil
report.  The information should provide the designer with enough
information and recommendations for a foundation. These can be the following:
a.	Pier
b.	Ground set (pole set in embedded corrugated pipe) in concrete filled
tapered hole.
c.	Spread footing - square, round or octagonal.
d.	Pedestal on piles

One of my recent pole projects had a 14 foot high by 30 foot diameter
octagonal concrete pedestal sitting on 16 - 30" diameter piles 80 feet deep.

Some of the things that a foundation designer requires is the allowable
passive pressures, where the passive pressure starts and what the maximum
passive pressure can be.  For a spread footing, one also needs the
allowable bearing pressure.  The soil report should also inform the
designer what the factor of safety for these values are.  Also, the
designer should provide a set of his foundation calculations to the soil
engineer to insure that the designer has used the soil report information
correctly.  In the past this has been a problem with some soil engineers
providing "boiler plate" statements that don't fit the particular situation.

Sometimes, the soil engineer will tell you that the ground water is at
surface level.

There is also a commercial program that will design the pier using Broms
method.  In some cases, the soil engineer will design the pier footing
after the structural designer has provided the lateral and overturning
moments.  If you use this, make sure that he certify the foundation
drawings as well.

I presently have a spreadsheet (not for sale) that will design poles to 900
feet and will size a pier, ground set or a spread footing.  It's not
completely automatic as it allows you to play "what if" to provide the most
economical pipe sizes in a variety of standard lengths.  I know of a few
other pole designers who have better spread sheets than this.


At 01:20 AM 12/10/2001 +0300, you wrote:
>Neil,
>
>Well, in my opinion this program in spread sheet should be useful. You'll
>appreciate, the calculation of wind moments at the base is quite a tedious >exercise; you tend to make mistakes also, if you are attemting to do it by
>first principle.
>
>Also, you have to start with an assumed size of footing which you will
>establish thru preliminary calculations. Once you have established the wind >moments, the actual task of satisfying the stability requirements begin. The
>initial  assumed size of footing may not work, so you have to revise the
>size of footing & begin those steps all over again. And, it might take a
>couple of trials before you really settle down with a size that actually
>satisfies the stability requirements. Manual calculation would become
>tedious while the program would help you with as many trials as are required
>to fix a final size of the footing.
>
>And, once the size of the footing is established, the design of spread
>footing is a child's work, really.
>
>SYED FAIZ AHMAD; MENGG, MASCE
>SENIOR STRUCTURAL ENGINEER
>SAUDI OGER LTD
>RIYADH, SAUDI ARABIA.



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