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Re: Residential Design Spreadsheet

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I agree that Dennis' effort is commendable, but I offer the following as a
warning to others who may have a desire to use it.

I too tried Dennis' spreadsheet and found numerous errors and
inconsistencies in the first one-half hour of use.  I sent Dennis an email
and I assume that he corrected the errors that I found.  The major errors I
found were in the portion that calculates the deflection of the diaphragm
according to the UBC formula.

To be fair, this was some time ago, and perhaps most of the earlier bugs
were corrected.  However....

This experience lead me to question the entire basis of the "rigid
diaphragm" portion of the spreadsheet, since proper calculation of the shear
wall deflection under a given load is essential to determining the
stiffnesses of the various shear walls in each line (the shear wall
deflection formula in the UBC is similar to the diaphragm deflection

[As an aside, I believe that the formulae mentioned above have not had
rigorous confirmation by tests, and are of limited use, since there are
several published papers that have questioned the validity of these

In addition, since Dennis' spreadsheet is for multi-story buildings, how
does he account for the fact that the shear walls below the top story will
not be cantilevered (single curvature), but will be fixed top and bottom
(double curvature)?  The shear wall deflection formula in the UBC is for a
cantilevered wall.  Is it adjusted to a fixed condition when there are walls

As a further point, are the stiffnesses of each wall in a common line simply
added algebraically, or are they combined into a single equivalent stiffness
for that line, as would be done for concrete or masonry walls?  How is the
non-linearity of the walls accounted for?  Is iteration done?

This is just the tip of the iceberg, and is confirmation of Bill Allen's
point that all of this needs to be documented.  The process of documentation
into a help file (or whatever form) is a chance for the author(s) to clearly
understand his/her own intent, and will, in itself, lead to the discovery of
other bugs to be fixed.

In the time it would take a user to verify the intent, validity, and
accuracy of the spreadsheet, s/he could do the calculations for 10 complex

CAVEAT EMPTOR (even if it's free!!)

Mark Swingle


on 25 July 00, Bill Allen wrote:


<<I'm not sure if the statement you made is fair.
  If so, and extrapolating, NO software would need
  manuals or sample problems because we ALL know the
  theory behind it, right? You F.E.M. guys don't
  need no stinking manuals, right :o)?

<<IMO, ALL spreadsheet templates (even/especially
  interoffice templates) should have documentation
  by the author with samples available.

<<I believe I am quite familiar with the Code but I
  am reluctant to dive into Dennis' spreadsheet
  because there is a lack of documentation and samples.

<<Sad, but true.

<<Just my opinion.


<<Bill Allen, S.E. (CA #2607)
<<Laguna Niguel, CA

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