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Tilt-Up Wall Pier Design

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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 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 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.


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