Staad.Pro v8i results

[ossipent]

I'm using Staad.Pro v8i Release 20.07.05.15 for structural analysis of a steel structure. I'm using Eurocode EN 1993-1-1:2005 in Staad for the analysis (might be that many of you here are not using use Eurocode, but still). The problem is that basically I've been looking at the utilization ratio of a part of a truss lower chord. When I analyze the structure with Staad 2006 version it works fine (checking also by hand). If I run the same structure in v8i, the unity check results are totally different.

There is max 100kN of compression and 500kN of tension (and small moments). For some reason v8i selects one basic load case a critical case (it's wrong and has also been checked by hand) and outputs a utilization ratio of 9%. The buckling lengths are really small so it's not about that.

If I run the analysis in 2006 version, the ratio is over 40% and it corresponds with the combination case causing the biggest tension as it's more critical in this case (compression is small in relation to buckling lengths, tension much bigger and critical in this case). In both models the member forces are similar.

So it seems that for some reason the critical load case is selected wrongly by Staad in v8i.

Has anyone come across with a problem even close to this when using Staad v8i?

Thanks.

 

[dozer]

I've had the opposite problem. When using the direct analysis method and the advanced analysis engine in release 20.07.05.15, it sometimes gets unreasonably high local z shears and local y moments for some members. I haven't been able to figure out the common denominator in files that experience this but it happens quite often. I have found STAAD to be getting more and more unreliable as they add new features.

For your issue I would check to see if you've defined the LOAD LIST command with the wrong load cases. If this is OK I would turn TRACK to 1 or 2 or whatever the highest level for the Eurocode is and see if that gives you any insights.

You might also try using LOAD LIST to force it to check only the case that you think controls and see what that looks like.

Good luck!

 

[Sye123]

Regrading the DIRECT Analysis issue, I would suggest that you start using the version 20.07.06.34 which has adressed all these limitations. These high My moments were resulting from negative terms in the diagonal which were not handled in earlier versions like 20.07.05.15.

Regarding the EN 1993-1-1:2005 issue, two very useful suggestions have already been provided by dozer. You may actually have two seperate blocks of design, each one with a different LOAD LIST command and check whether you get a higher ratio for a case that you think should be more critical. The TRACK 2 output would list out the capacities as well which would help in checking. If these do not help, please go to

http://www.bentley.com/serviceticketmanager/

and create a service ticket and attach your model to it and technical support staff at Bentley will respond to your question.