I know I'm commenting my own question, but I just received the answer from the ETABS support: ETABS uses Scissors Model (in case there's someone out there looking for this info. Hope this helps). :)

https://wiki.csiamerica.com/display/etabs/Panel+zone+and+rigid+offset

Dear Rafaela,

As you know, the Ibarra- Krawinkler Model is simulated by using a spring rotation model. This modeling must be carried out by using Open Source Programs, such as OPENSEES. The plastic rotation can be considered by using Panel Zone. First select element>Panel Zone>Modify>User Defined Nonlinear Properties>Nonlinear>Modify>Then defined your rotation capacity.

The isotropic or kinematic models are usually used for steel structures. Please note that stiffness degradation and strength deterioration are not considered in these models. The degrading model (In Etabs from the hysteresis box) is suitable for modeling stiffness degradation and strength deterioration. Please note that you should equate the degrading model with the Ibarra-Krawinkler hysteresis model (I am not suggesting because the Ibarra-Krawinkler model contains collapse modes). Moreover, the ASCE/SEI 41-17 can be a good reference for determining the plastic rotation capacity of elements.

Thanks for all the answers.

My question though was not on how to include the panel zone in the model. I wanted to know which mathematical model ETABS uses when automatically assigning a panel Zone. In the manual it’s not mentioned explicitly, so I messaged the tech support team and they told me ETABS uses the Scissors Model to compute the properties of the rotational spring. So, problem solved! :)

Thank you all for taking your time to answer.

Cheers,

Rafaela

Take a look on Extreme Loading for Structures software. Best structural analysis software for non-linear structural analysis.

Extreme Loading for structures software ELS is a high fidelity numerical analysis tool for analysis of structures under the effect of extreme loads like blast, progressive collapse, seismic, impact and in general performance based design. We adopt a numerical analysis method called “Applied element method (AEM)” which is similar to FEM except that it allows for elements separation and hence you can visualize the collapse shape of the structure in case failure occurs.

Since your interest is in Seismic so I believe this tool will be a good fit for your needs since it allows for the following:

1) Time History Analysis

2) Push over analysis

3) Blast Analysis where blast loads can be generated from UFC code or User can import Blast pressure. Also we have the capability of importing CFD analysis as a pressure loading.

4) Automatic plastic hinge formation

5) Stresses and Strains Output

6) Internal Force Diagram output

7) User can define locations and shapes of pre-existing cracking or corrosion areas inside the model

8) User can model layers of FRP used for strengthening

9) The ability of modeling different masonry units arrangements. For example, English bond or Rate trap bond.

10) Non-linear material models for concrete, steel, brick, mortar and glass or even user defined material models.

11) Our solver is much more faster than any other FEM tool like LS-Dyna/ANSYS.

12) Nodal Compatibility is not required in the meshing which gives user the ability to customize the meshing easily.

Rafaela Sanches In Sap2000 or Etabs the rotational springs are based on the so called scissor model that approximate the shear deformation of the PZ.