Beam and column ultimate rotation(Plastic+yield)

[n_siahpolo]

Dear all

as demand rotation ductility of beam and columned is the ratio of ultimate rotation to yield rotation of beam or column, my question is if we choose nonlinear beamcolumn element (force deformation) with which command Opensees reports beam and column ultimate rotation? I know the definition of chord rotation but my desired parameter is ultimate rotation of beam and column.
Element rotation ductility demand=theta(u)/theta(y)

[vesna]

There is no output for ultimate rotation in OpenSees as it depends on materials assigned to fibers of a section. By looking at the chord rotation you should be able to get values of ultimate rotations. You can also write a small code in tcl to output ultimate rotations.

[n_siahpolo]

dear Vesna
Hi, thanks for your reply.
May i ask you to help me how can calculate the ultimate rotation of beam and columns by chord rotation results?
I am really confused about this subject. As i see in some posts users tell if the ultimate chord rotation is required it is better to use plastic hing. But in my model, i prefer to use fiber elements.

[vesna]

You need to set limit strains for your materials in order to get ultimate rotations. You can do that by using MinMax material (http://opensees.berkeley.edu/wiki/index ... x_Material).

Alternatively, if you have softening response of your structure you can also determine the ultimate rotations as rotation at which you observe 20% strength loss.

[IsmBaha]

Hello Vesna,

Do you mean 20% loss in global strength of a column, such as 20% loss at baseshear-topdisplacement response of the structure? it can't be in local response bc e.g., cover concrete can be spalled and completely gone so this doesn't mean it is at the ultimate rotation.

Also, what is "limiting the strains" of materials (all concrete & steel materials?) provide to get ultimate response (rotation)?

Thank you in advance.