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RE: tilt-up concrete walls

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>
>Does anyone know of a good resource for formula
>derivation for the allowable axial load and bending moment
>in tilt-up concrete walls?  I have several seminar reference
>guides with "idiot" tables giving Pult with a specified
>data.  Interpolation is required for intermediate values and
>can be time consuming.  I figured I would simply create a
>spread sheet that could derive these ultimate loads but not
>been able to find the required equations.  Because these walls
>are so slender, the standard concrete column formulas are
>inadequate.  (even these exact formulas are difficult to find
>for the different rebar layouts)
>I'm assuming the formula uses something more than just a
>moment magnifier as used in long columns, but I could be
>wrong.
>
>Mark Pemberton, P. E.

Dear Mark:

The problem with most tiltwall references, programs, and spreadsheets is
that they assume continuous or near-continuous footings (i.e., long
bearing lengths).  When the bearing lengths are relatively short, the
formulas quickly yield results which are absurdly conservative.  In
Texas, due to our expansive clay soils, tiltwall panels typically span
between drilled pier supports, with one pier at each panel joint.  Thus,
for 24 inch diameter piers (typical), the panel bearing lengths shrink
to just less than 12 inches.  Until now, no rational analysis method has
been available for this situation.

The Structural Engineers Association of Texas (SEAoT) has recently
addressed this problem in it's new publication "Concrete Tiltwall Panels
Supported on Pier Foundations", which includes a very useful Excel
spreadsheet template.  For further information regarding this
publication, I recommend that you contact either the SEAoT State
Secretary, Jon Jelinek, at debjon97(--nospam--at)aol.com, or the principal author,
Paul Rielly, at prielly(--nospam--at)halff.com.

Hope this helps,

Stan R. Caldwell, P.E.
Vice President

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