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SAP2000, RISA3D, and STAAD[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: "SEAOC (E-mail)" <seaoc(--nospam--at)seaoc.org>
- Subject: SAP2000, RISA3D, and STAAD
- From: gluth(--nospam--at)klaa.com (Gregory P. Luth)
- Date: Mon, 15 Dec 1997 19:01:01 -0000
- Encoding: 39 TEXT
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
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