Post Bifurcation analysis of a column

[fpereira77]

Hello,

I need some help.
I'm working on my dissertation for college and I want to study the post-bifurcation behavior of a column, with a non linear (bi-linear) material, studying the relationship between the applied load and the transverse displacement at the mid-span. With this in mind, I developed a function in Matlab and I wanted to compare it with results from finite element programs. I'm currently working with ADINA(900 nodes) and although I was able to get results with the program they don't match the results I get with my MATLAB function. The trajectories are pretty similar, but the maximum load and displacement (at the maximum load) don't match. Basically the Beam model consistently gives results above what I get in my function, while the plane stress models results are below.

Therefore, I would like to use SAP2000 to make the same analysis and compare with the other results. The problem is that, although I have used sap2000, I have no idea how to make this type of analysis. I don't know which load patterns/cases to create and run. I think this is a pushover analysis I want to make, since I want to apply an increasing axial load to the column from the value 0, have the column, at some point, bifurcate, and then get the trajectory Transverse displacement vs applied load.
Can someone please help, or is this too complex to explain here?

By the way, I'd like to do these with both a beam model and a plane stress model.

Thanks

 

[stressed]

Your question is not so clearly worded. When you say "bifurcation" are you referring to geometric nonlinear behavior (buckling), or material nonlinear behavior, or both? Is this brittle material or ductile? More information is needed in order to reply.

 

[JoshPlumSE]

Have you considered Mastan? For academic purposes, for steel columns, I suspect it will be more useful than SAP. And, it's free.

 

[JasonMcKee71]

Apparently he is referring to buckling.

Jason McKee
proud R&D Manager of
Cross Section Analysis & Design
Software for the structural design of cross sections
Moment Curvature Analysis
Interaction Diagrams
Reifnorcement Design etc.

 

[fpereira77]

I believe post-bifurcation and post-buckling are synonyms referring to the same aspect of columns' behaviour. Bifurcation load = buckling load. Sorry if that wasn't clear.
By now, I've surpassed the problems I had when I made this topic, since I figured out what was wrong with my ADINA finite element models, so I'm no longer interested in developing the same models in SAP.

 

[JoshPlumSE]

Just to clarify my earlier post, because I have been accused of showing some anti-SAP bias.....

Bias alert: I work for a company that can be considered a competitor to SAP. Though definitely not for the type of advanced analysis mentioned in this post.

I would normally recommend SAP as an alternative to my company's software for advanced analysis that we cannot handle. However, that is usually for more large scale commercial projects where the models have many members and elements. Where an easy to use commercial program would be more appropriate.

For a very academic exercise like this appeared to be (investigating in detail the behavior at a single column) I believe MASTAN is the gold standard that the academics use. It's not very easy to use and you probably would not want to use on large scale projects. But, for a single column model, my belief is that it is supposed to give the most accurate behavior.

Now, I cannot pretend to be an expert on the subject as I don't often do this type of analysis myself. I pass this information along based on the experience I have from attending many of the AISC committee meetings over the last 10 years or so. The PhD's who present and debate new research at those meetings tend to use MASTAN to show the "true" behavior of steel members in buckling and post buckling and such. Hence the reason why I thought it would be useful to the OP.