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SAP2000, RISA3D, and STAAD

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We've had good luck with the SAP products, but have taken to writing our 
own pre and post processors working in visual basic and Excel to get a 
reasonable turn around on our analysis/design cycles.

RISA was a very good product when it first came out, but we have had 
problems with it lately.  The first problem had to do with torsion on a 
wide flange shape.  We were analyzing a steel structure that relied on 
torsion in several of the beams for strength and stiffness.  The results 
from RISA suggested that a wide flange beam was as effective as a tube.  On 
further investigation, it turned out that this was the case only when you 
used the RISA database shape.  If we input all the properties, including 
"J", manually, the results were substantially different.  Our conclusion is 
that RISA is using warping torsion properties for all torsion problems, 
even when they are not appropriate, as for long beams where the warping 
"boundary" affect has little influence on the overall behavior.  This bug 
is exceedingly dangerous because even with short beams, warping torsion can 
only be used if the bi-moment is resisted at the support.

We've also gotten strange results when we tried to use the plate elements 
in RISA3D.

STAAD was a great program in 1987.  Since then its gone down hill.  We 
stopped using it after we tried analyzing a cantilevered tapered section 
and found that it didn't satisfy statics.  It was off by 10%!  The rep told 
us it was the numerical error involved in doing a tapered section.  We also 
tried using the master-slave feature to model a diaphragm and got some 
strange results because of the way the feature was implemented.

My advice is to treat all results from analysis programs as wrong until 
proven right.

Gregory P. Luth, Ph.D., S.E.
Krawinkler, Luth, & Associates, Inc
160 Jefferson Drive
Menlo Park, CA  94025
PH:	650 688 4710
FAX:	650 688 4712