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RE: The Most Ridiculous Item of the Day (with apologies to Bill O'Reilly)

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Bill,

I don't think that the code provisions that Sharon pointed out would
really apply as they are intended for R/C moment frames under seismic
loads.  While your situation is certainly gonna be under seismic loads, I
am not sure that it should be classified as a "frame".

As to the code section the plan checker is referencing, I agree that I
doubt s/he really meant 1910.16.8.6.  S/he probably really meant 1910.9.1,
which would land you in the same spot (i.e. minimum steel of 1%).

Your best arguement comes from section 1910.3.3.  It basically states that
for flexural members, if the design axial load strength (phi*Pu) is
smaller than 0.10*f'c*Ag or phi*Pb, then the ratio of reinforcement shall
not exceed 0.75 of the ratio phob (balanced reinforcment ratio) that would
produce balanced strain conditions for the sections under flexure without
the axial load.  I think that is what you might be looking for...

HTH,

Scott
Adrian, MI


On Wed, 11 Jan 2006, Sharon wrote:

> Bill
>
>
>
> I have notes from a class where Mr. Gosh (concrete guru) stated as a
> rule of thumb:
>
>
>
> For Pu (Gravity only)
>
> If Pu <= 01AGf'c then design as beam, 1921.3
>
> If Pu > 01AGf'c then design as column, 1921.4
>
>
>
> Good Luck
>
>
>
> Loving California,
>
>
>
> Sharon Robertson, P.E.
>
> Arcon Engineers
>
> sharon(--nospam--at)arconengineers.com
>
> Tel: 858-503-7854
>
> Fax: 858-503-7858
>
> ________________________________
>
> From: Bill Allen [mailto:T.W.Allen(--nospam--at)cox.net]
> Sent: Wednesday, January 11, 2006 7:39 AM
> To: seaint(--nospam--at)seaint.org
> Subject: The Most Ridiculous Item of the Day (with apologies to Bill
> O'Reilly)
>
>
>
> Now I know I have finally made it to the Big Time (tm). I have recently
> been retained to design a light standard foundation. The light standard
> is 5" square and 25 feet tall with a light fixture at the top. The
> footing projects 2'-6" above grade and is 2'-0" in diameter. The
> installation is in Southern California (BTW, it's going to get to 70o F
> today) which means I have designed this "structure" to the 1997 UBC /
> 2001 CBC.
>
>
>
> The "project" was plan checked by an outside consultant who shall remain
> unnamed. The plan checker is an SE and his number is only about 400
> higher than mine. At a passing rate of 100/year, that means he probably
> passed in 1987-1988 or so. So, it's not like he's a neophyte.
>
>
>
> I've got a plan check list consisting of six items, four of which are
> structural.
>
>
>
> I'll limit my post to The Ridiculous Item of the Day. Since the top of
> the footing projects 2'-6" above grade, he is requesting that the
> footing be designed as a concrete column with a minimum reinforcing of
> 1%. He is citing CBC section 1910.16.8.6 but I believe he really means
> 19.10.1 since the footing is not a composite section. For a 2'-6"
> diameter section, this means I need to provide (don't laugh) 9-#8 bars!
>
>
>
> Now, I can find a few references to reinforce (sorry for the pun) my
> argument that this section is not a column (Pu<0.10f'cAg, d/L>3, tension
> controlled section, etc.), but I seem to recall a section of the code
> where it was very clear that, if Pu<0.10f'cAg, then the section can be
> considered a beam and not a column. Unfortunately, I can no longer find
> that specific section in the code.
>
>
>
> Is this still applicable? Am I dreaming that there is an exception in
> the code?
>
>
>
> Thanks,
>
>
>
> T. William (Bill) Allen, S.E.
>
> ALLEN DESIGNS <http://www.AllenDesigns.com>
>
> Consulting Structural Engineers
>
>
>
>

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