moment resisting frame with steel-concrete column

[masoudahmadi]

hi
i modeled concrete filled steel tube section as a column in moment resisting frame. The nonlinear beam-column element model with distributed nonlinearity is implemented. also, The steel simulated by Steel02 model.
i compare my results with experiment. The comparison shows that unreasonable accuracy has been occurring for OpenSees in predicting the cyclic behavior of the frame with concrete filled steel tube columns. as you know, under compressive loading steel components are susceptible to outward local buckling and under cyclic loading additional modifications are necessary to properly model the local buckling response. i think effect of buckling do not consider in my model when i used steel02.
what is the best material for modeling steel tube that consider outward buckling and improvement accuracy of results?
thanks in advance for your sincere cooperation.

[fmk]

the results are only as good as your model .. as you are gettign unreasonable results, your model is probably poor .. for example you talk about buckling, but you will not get a single column to buckle unless you create a model which will allow it to do so, which typically involes splitting it in 2 and providing some initial imperfection.

[baozai]

fmk wrote:
> the results are only as good as your model .. as you are gettign
> unreasonable results, your model is probably poor .. for example you talk
> about buckling, but you will not get a single column to buckle unless you
> create a model which will allow it to do so, which typically involes
> splitting it in 2 and providing some initial imperfection.

Hello, Frank:

For doing Buckling analysis in OpenSees, is there any special algorithm or hints we need to take care of?
Thank you for your help.

[fmk]

use gooogle to search for how people model braces .. basically you need to create an imperfection in the column, a.k.a. a mid point .. you give it an offset around of magnitude around those permitted in facbrication .. here is something to start you off

http://opensees.berkeley.edu/wiki/index ... n_elements