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Re: Minimum Reinforcing in Compression M

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Dave-
I've been tempted to just let this go, but I suddenly feel compelled to share my thoughts. I've been building, engineering, and reviewing other engineer's work from time-to-time for almost 30 years (mostly on sloped lots with drilled pier/grade beam foundations). I have never seen or heard of  such a massive amount of steel in a drilled pier.  These piers aren't really the same thing as free standing compresion/bending columns whose failure would produce a catastrophic collapse of the building. I've never seen, or heard of, a failure in one of these piers.
1. Are you building on a steep lot without the services of a solid engineer?(I wouldn't.)
2. 2' dia. piers are large for a normal residential design (Is it an inordinately long way to solid material or are the soil's design values unusually low?)
3.  It doesn't sound like the Building Dept. is "bad-mouthing" you, they're just sharing their observations regarding local design practice(And trying to do you a favor.)
4. You might want to ask yourself why your design is so much at odds with your peers (or maybe you've discussed this with some other local engineers).

Obviously it is your license on the line and you have to do what you think is right.  But unless there is something really unusual about this site, I would not not recommend using 4 to 6x the pier reinforcement that everyone else uses based on your personal lawyerly interpretation of the code. (I suppose you could call ICBO and get a code interpretation from them.) If  I was the owner (developer?) I would be seriously thinking about changing engineers if I saw very much of this in your design work.

This post (and your local feedback) is offered in an attempt to assist you, no one is telling you to violate the code.  But your design just does not look reasonable for typical hillside construction.  Let's just say for the sake of discussion that  a pier failed; your standard of care is local practice and you'd be fine--but do you real think these piers will fail if you don't stick 15 pieces of steel in them?
C. Utzman, P.E.

Dave Browning, P.E. wrote:
Thank you, Scott and Roger for your help.  I'm going to tell the building
department that I won't stamp the plans with less than what the code
requires unless they can produce some sort of local amendment.  I don't know
why they care, anyway.  Aren't they just checking for code compliance?  If
I've called out more steel than what THEY think the code requires, then
shouldn't they just move on with their processes?  Why do they have to
badmouth me to the homeowner?  Oh, well.  Good thing its Friday.

Oh, and Scott.  Yes, I am an idiot.  I meant 1% Ag, not 10% Ag.  I realized
my mistake about 2 nanoseconds after I hit "Send."  I considered sending a
follow-up clarification but then I thought I'd leave it alone and see if
anybody is paying attention.

Everybody:  Have a great weekend!  And if you're working, think of me.  I am
too.

-----Original Message-----
From: Scott Maxwell [mailto:smaxwell(--nospam--at)engin.umich.edu]
Sent: Friday, August 01, 2003 10:01 AM
To: seaint(--nospam--at)seaint.org
Subject: Re: Minimum Reinforcing in Compression M


Roger,

You are (of course) completely correct.  That is the other reason listed
in the commentary for section 10.9.1 of ACI 318 (same as the UBC section
1910.9.1).  But, I neglected to mention it.  Thanks for correcting me.

HTH,

Scott
Ypsilanti, MI


On Fri, 1 Aug 2003, Roger Turk wrote:

  
Scott Maxwell wrote:

. > The minimum steel requirement is supposedly there due to the potential
    
for
  
. > bending, even if there is no apparent bending on the member.

Scott,

It is my understanding that the minimum reinforcing in compression members
    
is
  
to account for creep and shrinkage stresses in the concrete.  Creep and
shrinkage stress tests in the 1930's showed that low volumes of
    
reinforcing
  
can yield due to creep and shrinkage, therefore not contribute to the
capacity of the compression member.  The minimum reinforcing requirements
    
are
  
to ensure that there is sufficient reinforcing present so that it will not
    
be
  
at yield due to creep and shrinkage.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

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