Where I work, we have been using SELECT series 4 for a while and are finally looking to upgrade to SELECT series 6. I am comparing the two versions and have found a significant difference in analysis results for direct analysis.
The model below is of a Baghouse and is built up of plate and beam elements. Initial analysis was done using "PERFORM DIRECT ANALYSIS ASD". SELECT series 4 performed the analysis and was stable. I then performed the same analysis using SELECT series 6 and the results were very different. As you can see in the images below of the displacements (at the same scale) SELECT series 6 shows instabilities whereas SELECT series 4 does not.
SELECT series 4 |
SELECT series 6 |
The following is a series of analyses that I performed to determine where the analysis engine might have a difference.
- Ran Direct Analysis (SS6 shows instabilities)
- Ran P-Delta Small Delta Analysis (SS6 shows instabilities, similar to 1)
- Ran Elastic/First Order Analysis (Results Same)
It would seem as the P-Delta analysis engine has changed between the versions. After looking at the version release notes between the two versions, I could not identify the reason why this would would happen. Maybe there has been some changes that I am unaware of?
I hope that someone here has insight on what the reason for the different results. We will most likely not be able to adopt SS6 until I can figure this out.
Thank you for your help!