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PCAcol BUGS

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Because the use of PCAcol to solve irregular column problems was 
suggested in another thread (Odd Shaped Concrete Column Software) 
late last week, now is a good time for me to report to the list some 
bugs that we have found.  These bugs exist in both version 2.3 and 
3.0 of PCAcol (with IRRCOL).

The result of the bugs is that, for some conditions, the capacity 
calculations that are performed can be off by more than a factor of 
2.  When it occurs, the error produces results that are always 
UNCONSERVATIVE.

The error seems to be limited to cases where the principal axes of the
section are not parallel to the X and Y axes.  This could be a problem
for any section that is not doubly symmetric (for instance, L-shaped 
walls or generally-shaped sections) or for doubly symmetric sections 
that have been rotated.

Under the conditions defined above:
   - uniaxial design checks (P-Mx or P-My) and the corresponding
     diagrams displayed on the screen are incorrect.
   - biaxial P-M diagrams (for all angles) are potentially incorrect.
   - the biaxial constant-P contours (plots of Mx versus My) and 
     the design checks appear to be correct.

The problems with biaxial P-M diagrams were reported to the developer 
almost a year ago.  Although we understood that problem would be 
fixed with version 3.0, it was not.  The problems with uniaxial 
checks and diagrams were discovered recently.  They can be seen by 
reviewing the capacity checks (uniaxial moment demands using 
both uniaxial and biaxial calculation methods) and comparing P-M(0) 
with P-Mx and P-M(90) with P-My diagrams.

The problems became apparent to us when checking the simplest 
possible "irregular" section--that is, a regular, rectangular section 
that has been rotated.  We expected rational results (same failure 
surface, but rotated).  This simple situation revealed the problem; 
we've also confirmed it with more complex situations.

The old bugs have been re-reported and new bugs reported to the 
developer.  Until the bugs are fixed, our designers are doing one of 
the following:

1) using a different design method (for instance, in-house software, 
    design charts, or hand calcs), or
2) orienting all sections in PCACOL with the principal axes        
    parallel to the X and Y axes (which requires calculation 
    of the correct orientation) and selecting the biaxial calculation 
    method.  (Making sure that the orientation of the loads matches 
    the orientation of the section in PCACOL.)

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Michael Valley                                   E-mail: mtv(--nospam--at)skilling.com
Skilling Ward Magnusson Barkshire Inc.                  Tel:(206)292-1200
1301 Fifth Ave, #3200,  Seattle  WA 98101-2699          Fax:        -1201