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RE: non-constrained embedded pole - 97 UBC 1806.8.2.1 "d" definit ion

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Nels:


Thanks.  I found a 1970 UBC lying around and the "d" definition indicated
the maximum depth is 12 feet for computing lateral pressure but all table
has is the value may be increased 2* for 1/2" allowable deflection.  The 15
times increase was included in the table in the 1973 building code [typo?].

My take is the "d" definition 12 foot max for pressure should always apply
for the formula and the 15 times should be for other stuff.  I don't think
it will normally make a difference however.


Thanks.

Scott M Haan P.E.
Plan Review Engineer
Building Safety Division 
Development Services Department
Municipality of Anchorage
http://www.muni.org/building
phone:907-343-8183  
fax:907-249-7399
mailto:haansm(--nospam--at)ci.anchorage.ak.us



-----Original Message-----
From: Nels Roselund, SE [mailto:njineer(--nospam--at)att.net]
Sent: Wednesday, November 21, 2001 2:05 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: non-constrained embedded pole - 97 UBC 1806.8.2.1 "d"
definition


Scott.

The embedded pole formulas and definitions are unchanged from at least the
1970 edition of the UBC.  The format and values of the Tables differ.  In
1970, the increase per foot of depth was given with an allowable doubling of
that increase for flag poles and signs.  An arbitrary maximum value was
given in another column, and instead of being 15 times the increase, it was
a value specific to each soil type [some more than 15 times the allowable
increase, some less].

In 1970, I believe it was clear that the depth of footing may exceed 12
feet, but for depths greater than 12 feet, that the maximum lateral bearing
value is to be based on the value at 12 feet [a trapezoidal lateral bearing
diagram].  If the doubling of the rate of increase was used, the maximum
value would be the arbitrary maximum value, even if it was reached at less
than 12 feet.

The 1997 UBC can't be interpreted that way, but that may have been its
intent.  To produce that intent, the phrase, "to a maximum of 15 times the
designated value" needs to be moved from the end of the first sentence of
footnote 3 to the end of the second sentence of footnote 3.

Maybe you are checking plans prepared by another old-timer -- caught by an
obscure and [perhaps] unintended code-change .

Nels Roselund
Structural Engineer
South San Gabriel, CA
njineer(--nospam--at)att.net



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