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RE: Tilt-Up Wall Pier Design

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Rich,

I think you have it right when it comes to designing a pier with axial stress greater than 0.06f'c.  

As for the horizontal ties, I believe the code states that they shall extend beyond the openings for at least the development length of the largest vertical bar.

Hope that helps,

Doug Mayer, SE
Structural Engineer
 
TaylorTeter
Partnership
 
 
-----Original Message-----
From: seaint04(--nospam--at)lewisengineering.com [mailto:seaint04(--nospam--at)lewisengineering.com] 
Sent: Tuesday, May 15, 2007 12:06 PM
To: seaint(--nospam--at)seaint.org
Subject: Tilt-Up Wall Pier Design

I have a question concerning tilt-up wall design of piers around
window/door openings.  I have conditions where the stress in the pier
exceeds 0.06*fÂ'c.  This is the limit of ACI 14.8.2.6 for using the
empirical slender wall design.  I have a copy of Â"The Tilt-Up Construction
and Engineering ManualÂ" 6th edition.  In this manual it states that the
ACI 14.8.2.6 requirement is a strength conversion of the old UBC
requirement of 0.04*fÂ'c for allowable stress design.  It (the manual)
states that when the stresses exceed 0.04*fÂ'c then the pier must be
designed as a column.  I donÂ't find anything like this mentioned in ACI,
but it makes sense.  I see contradictory information in the manual for
design of in-wall columns.

It seems to me that if it is designed as a column then the vertical
reinforcing has to be a minimum of 0.01*Ag of the pier.  It also appears
to me that the horizontal reinforcing must be enclosed ties and that cross
ties will need to be placed at every other bar.  Am I interpreting this
correctly?  Are there other ACI loopholes that allow less steel and no
ties?  If I require closed ties, how far above and below an opening would
they extend before they are not needed any more.  I am wondering about
this in the case of a two story panel where the pier is only on the lower
story.  It doesnÂ't make sense to carry the ties full height to the roof.

Thanks for your help.

Rich


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