CFT modelling

[huffte]

I would suggest a literature search to determine the strain at which CFT buckles locally as a function of the D/t ratio. You could then manually specify a performance criterion which notifies you that the strain has been reached.

[Madeha]

I tried this method as well, and in that case, the performance criterion was reached very early, at a scaling factor of 0.5 during the incremental dynamic analysis. However, the loading was continued until the scaling factor reached 1.3 for the global buckling scenario. Does this imply that my frame buckled at just 0.5 IDA, which is significantly below the full demand of the input ground motions? Is this result practically reasonable?

[huffte]

Based on my experience, buckling of the tube in CFT construction generally constitutes a limit state beyond which additional loading is unacceptable. You could specify "Stop" rather than "Notify" in the performance criteria if you want the analysis to cease once the tube buckles. There has been a good bit of research on strain limits for CFT. I discuss some of these limits in a research report completed for the Tennessee Department of Transportation, "Best Practices for Bridges with Pipe Piles". The report is freely available and easily located by a Google search on the title. Best of luck!