rigid diaphragm-nonlinear element-progressive collapse

[hshoar]

Hello

I am modeling a dual system steel structure (moment frame with concentric bracing) for progressive collapse analyses. I developed my model with these specifications:
- It is a 2D model
- 10 story
- 3 bays
- material : Uniaxial material steel01 + MinMax material
- fiber sections
- Beam With Hinges element
- first bay is braced which I will remove a column there in first floor.

I have some problems as follows:
-how can I define a rigid diaphragm while I cant use equalDOF or truss element? because I'm using Beam With Hinges elements and I'm removing a column, so when I add a truss element it effects the vertical displacement of near removed column!
-I read somewhere that Opensees did not consider buckling in concentric braces. is this true? If yes, what should I do in that case?
-I have problem in defining Rayleigh damping. because I cant do eigen analyses when I remove a column (it fails in convergence). And I think assigning Rayleigh damping in progressive collapse should be different than other ground motion situations. Is anyone have any information in this case? ( I know this is not an Opensees question but if anyone have any suggestions I will appreciate!)

Thank you very much.

[hshoar]

its really sad not to get any response...conclusion: never post anything on off days!

[mhscott]

Your questions are a little vague, but at the same time require very detailed answers. That's probably why you're not getting a response. I would suggest doing a little more research on what you're trying to model and coming back with more directed, specific questions.