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RE: Tilt-Up Wall Pier Design

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First, you can spread the load out above and below the openings, at least
under the UBC 1997. Once the load has been spread so that the force is below
the threshold you could probably discontinue the column. As far as I know
you will need ties. You can treat it as an architectural column with 0.5%
reinforcement but you can only use half the section area which probably
won't work in a thin panel. I usually find that I usually need "columns"
only when I am supporting a floor with much higher loads than a roof. In
such cases my panels are usually 8" to 9" thick. You can, as an alternative,
increase the strength of the concrete to avoid columns if you are close.

Mark E. Deardorff, S.E.
Structural Engineer
Burkett & Wong Engineers
3434 4th Ave
San Diego, CA 92103
P 619.299.5550
F 619.299.9934
mdeardorff(--nospam--at)burkett-wong.com
 

> -----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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