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SAP for AISC Direct Analysis Method?

SAP for AISC Direct Analysis Method?

SAP for AISC Direct Analysis Method?

(OP)
Has anyone used SAP for direct analysis? If so, I'd appreciate it if you would share your knowledge and experience. I couldn't find any SAP documentation on direct analysis, but in version 11.02, it shows up in the steel design menu option when you change to AISC 360-05.

From a seminar I attended several months back, direct analysis method looks interesting, as it allows you do away with equivalent length K factors if certain criteria are met. If you google AISC Direct Analysis, you should find a good (free) Aisc paper by Shankar Nair on stability analysis. We just need to figure out what SAP is doing with direct analysis.

RE: SAP for AISC Direct Analysis Method?

The AISC paper by Shankar Nair is obviously biased as he chaired the Task committee who wrote this mess.  The Direct Analysis Method is anything but "direct".  This committee took a simple method used in building codes all over the world and mucked it up.  The notional load method is used in Canada, Australia, Europe and elsewhere by simply applying a small lateral load to account for geometric effects and residual stress.  It was elegantly simple and endorsed by ASCE, but apparently too simple for this committee.  Thanks to their meddling, the engineer must now iterate the stability solution using reduced stiffnesses.  It is no longer a Direct Method.  I can't believe they have the nerve to call it that.
 I did some grad work using SAP2000 with this method and comparing it to the true direct method (ASCE notional load method), but I haven't tried this new code in SAP2000.  I'm wondering how it will iterate the EA and EI stiffness modifications.  Of course its no surprise there is no documentation for this in SAP2000.  You can't find anything valuable on their nonlinear links either, just a bunch of theoretical stuff with no advice on how to apply it.
 If I appear PO'd about the state of code writing I am.  I think its really getting out of hand.  The IBC wind provisions are another example of committee hijacking.  These people don't have to use their handywork, they just want their name in a piece of the code.  What a joke.

RE: SAP for AISC Direct Analysis Method?

(OP)
I take issue with your characterization of older building code "simple methods" which in fact relied on complicated determination of K factors with alignment charts and all the exceptions to the alignment charts. No question in my mind that those methods were MUCH more complicated than K = 1 now permitted with Direct Analysis. More than that, those earlier methods were problematic in other areas. Take a simple cantilever column flagpole example with vertical load at the top using equivalent length method. We know for a fact that there are mill out of straightness and contractor out of plumbness effects which will result in moments at the base. Yet these "simple methods" using equivalent length factors would result in zero moments at the base, resulting in unconservative baseplate and foundation loads, no? I think Direct analysis method has a strong case to be made from both an ease of design standpoint and a practical standpoint.

Look, if you're going to criticize Nair and/or other code committee members, fair enough, this is a free and open forum. But please make your case from an educated, practical engineering standpoint, and back your viewpoint. Otherwise expect to get pushback from those of us who don't respect unsupported knee jerk assertions. I'm here to try and absorb viewpoints of others. But you seem to be making broadbrush claims without supporting your viewpoints. If I've mischaracterized your opinions, then please make your case as to why the Direct analysis method is so bad.

RE: SAP for AISC Direct Analysis Method?

It's good to hear that SAP now has the DAM.  No surprise that the documentation stinks up the place.  My only idea is to create a simple portal frame with a leaner column connected to it and play around with SAP to make sure I know what it's doing.

As for ELM vs DAM, the DAM might be more complicated than it needs to be, but the ELM is a travesty beyond description.  I'd venture to say that 95% of all structural engineers apply teh ELM WRONG because they just apply the alignment charts without adjustment.  All these adjustments are unbelievably difficult to apply correctly, even for engineers who are very interested in and experienced with steel design.  The DAM is a brute force, bulldozer method and is very easy to understand.  Assuming that CSi implemented it correctly, it should be much easier to apply correctly than the ELM.

RE: SAP for AISC Direct Analysis Method?

(OP)
Ok, we recently upgraded, and the new version has 2005 AISC documentation. Finally. The good news is that the documentation is very well done with a helpful how-to technical note on Direct analysis which walks you through the steps. You'll need V11.0.7 or newer in order to get the 2005 AISC documentation.

Based on my reading of Appendix 7 and the AISC seminar I attended several months back, CSI appears to have a real winner on their hands with their implementation of the DA method. They have done a really good job in the automation of it. Automatic reduction factors to section EI and EA depending on your choice of TAUb fixed or variable, they've automated the generation of notional loads, automatic handling of local P-delta analysis as well as sway per code requirements, and they also automate the creation of analysis cases used in P-delta. CSI appears to be paying closer attention to details.

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