AISC Advanced Elastic Analysis

[Settingsun]

Is Staad capable of the type of elastic analysis required for design according to AISC 360-16 Appendix 1, where compression member buckling is detected in the analysis? I tried the benchmark problem shown in Figure C-A-1.1 and Table C-A-1.1 of the commentary and didn't get a good match. I used PDELTA analysis with small-delta included and enough iterations to converge. These settings gave a good match to the benchmark problems for Chapter C.

If Staad is capable, what are the required settings?

 

[JoshPlumSE]

STAAD is probably not capable of this type of analysis. My comments on the subject:

1) I'm not a STAAD expert. I've used the program a number of times over the past 25 years. However, it's never been my primary program. In fact, I've worked for two of STAAD main competitors (RISA and SAP2000). So, I have an obvious bias / preference for those programs.

2) The challenge (as I understand it) applies mostly to members like wide flange beams or channnels. Members where column type buckling may interact with beam type buckling.

2a) By column buckling I'm referring to flexural buckling (strong or weak axis), and torsional or flexural-torsional buckling.

2b) By beam buckling, I'm referring to lateral torsional buckling.

3) My belief is the STAAD does not do a good job of modeling the torsional stiffness of wide flange and channel members. Nor does it do a good job of modeling the P-Delta effect on member torsion.
3a) RISA might do an okay job of modeling the torsional stiffness of these members, but it does not consider the P-delta effect on torsional rotation. At least not that I know of.
3b) I'm not certain about SAP. My guess is that it probably won't match the Appendix 1 benchmark example either.

4) You can see how these two types of buckling (column buckling and beam buckling) could significantly interact with each other and how this interaction is really, really important if your only code check is based on cross section capacity and you're relying on the analysis to fully account for any buckling effects.

5) That being said, it is possible that for other member types (HSS tubes / pipes, solid round or square bars, cruciform sections) this my not be an issue and that STAAD (or RISA and SAP2000) may be perfectly fine for Appendix 1.

6) Personally, I avoid appendix 1 like the plague.... I want to see some case studies where folks have used this effectively on a real world project before I feel comfortable with it. My guess is that this was added as a legal way for some university type folks to "push the envelope". But, that they don't expect it to be used by regular engineers.

I hope that helps.

 

[Sye123]

The stability analysis requirements spelled out in Chapter C of the AISC 360-16 specifications is fully implemented in STAAD.Pro. However the provisions of Appendix 1, go far beyond accommodating the pdelta effects (large + small), accommodating imperfections through notional loads and accounting for plasticity/residual stress effects by reducing stiffness. The Appendix 1 requirements (1.2 OR 1.3) is not implemented in STAAD.Pro.

 

[Settingsun]

Thanks, both.

The structure is a catwalk of two parallel trusses with floor at bottom chord level - a pony truss or U-frame stability problem. The members are hollow sections so no beam buckling issues. Appendix 1 would reduce to a check on the maximum stress from the analysis which is pretty attractive but I'd want to match the benchmark problem for open sections nonetheless.

The Australian code has had a framework (motherhood statements about advanced analysis being permitted provided it accounts for everything) for 30 years in anticipation that the software would become available for routine design. I was curious whether that day had arrived yet.

 

[JoshPlumSE]

The Australian code has had a framework (motherhood statements about advanced analysis being permitted provided it accounts for everything) for 30 years in anticipation that the software would become available for routine design. I was curious whether that day had arrived yet.

Yes, I think Appendix 1 is AISC's way of encouraging software companies (and engineering companies) of pushing the envelope. But, they're not really there yet. We're getting a lot closer though. I think if you look at some of the really advanced programs "perform-3d", some of the nonlinear versions of SAP2000 then you get pretty close... except for the interaction between torsion and buckling for wide flange members. There are, however, some academic programs (MASTAN?) that can probably do it. They're just not very well suited for creating larger structures.