Modelling buckling restrained bracing

[amy]

Dear Sir,
I would like to do a 2D model of a buckling restrained steel braced frame. In order to model the buckling restrained bracing, which element should I use? If I use the infrmFB element for bracing, does it behave like a buckling restrained as I am not modelling the initial imperfection? Or I have to use truss element? Any suggestions are highly appreciated.

Thanks
Amy

[ruipinho]

Amy, hi.

Yes, given that you will be running a 2D analysis, and hence restraining the out-of-plane DOFs of all nodes (typically: y, rx, rz), then the use of an 'infrmFB' element should indeed not give rise to a buckling behaviour.

In any case, and as usual, you might as well just give it all a go, trying different modelling options, and then see what comes out of it.

Good luck with your modelling efforts,

Rui

[amy]

Thank you sir for your suggestions.
Amy

[amy]

Hello Sir,
I have tried to model the buckling restrained bracing using infrmFB element but it shows in plane buckling though I restrained the out of plane DOF. So I changed to model the bracing with the truss element. As I have concentric cross braced bracing, the two bracings are intersecting at a common point. When I run the analysis it gives me a warning message "zero diagonal elements at the intersecting nodes" because I have used truss element for bracing. If I accept it and ask to run the analysis, the model runs and also gives me the eigenvalue. I also run nonlinear dynamic analysis and It works fine.

I am confused about should I use this model or I have to find something else?

Thanks in advance
Amy

[ruipinho]

Amy,

If you are managing to run the analyses that you wish to run, then I can only suggest you to continue along such modelling path.

Best,

Rui