Limit State Material (Elwood, 2004)

[RJM]

Hi all,

I am trying to use the Limit State Material formulated by Elwood (2004) which requires defining Shear and Axial Limit Curves. I can define the Limit State Material in STKO but cannot find the two types of Limit Curves. My question is whether they have been implemented in STKO and if so where can I find them?

Relevant OpenSees Wiki pages:
https://opensees.berkeley.edu/wiki/inde ... e_Material
https://opensees.berkeley.edu/wiki/inde ... LimitCurve
https://opensees.berkeley.edu/wiki/inde ... LimitCurve

Thank you very much for your help!

Best regards,

RJM

[marafini.f]

Dear RJM,

Thank you for your question!
Unfortunately, the command limitCurve in STKO is still under implementation. We arranged for its addition to the Limit State uniaxial material (Option 2) but it is not yet ready, so you won't be able to create

What is the objective of your material modeling? Maybe we can help you with a different solution.

Francesca

[RJM]

Hi Francesca,

Thank you for your quick reply!

I am trying to model a shear-critical reinforced concrete column. In my searching it seems that this is the best model to use but perhaps you can suggest something else?

Rico

[marafini.f]

Dear rico,

As for my knowledge, what you can do to model shear failure in an RC column is to define a uniaxial material which describes the desired behaviour, like for example Pinching4 (which has similar parameter to the Limit State Material you were researching) or ModIMKPinching, and add it to in a section aggregator when modelling your column as a forceBeamColumn element. You will be able to model the shear behaviour, but with uncoupled flexural and normal effects.

You can check out this webinar by Dr. Petracca
#06 Learning Opensees: Nonlinear Modeling of RC (Frame + Shear Wall) Structure (Distributed Plasticity) - REPLY
https://www.youtube.com/watch?v=Erdzh6fJRA8
and download the support files here https://asdeasoft.net/?webinar
to see how it is done in STKO.

Let us know if you have other questions on the matter.

Francesca

[ankurjain1992]

Hello STKO Team,

You guys are really doing a great job. Because of your help, I was able to conduct a lot of research work.

I am doing a Non-linear Time History Analysis on a structure which have nearly 12 short columns of 1.1 m height that are fixed at the base. Because of these short columns, I need to model Shear Failure also. I read that Elwood,2004 model is the best one to use. It is not present in STKO as I have checked.

So, my first question is
If I do not model Shear Failure in the short columns and directly do the Non-linear time history analysis then how can I get to know abt the shear failure?
I have seen in a paper "Probabilistic estimation of floor response spectra in masonry infilled reinforced concrete building portfolio" by Perrone et al. 2020 where he wrote "The beams′ and columns′ shear failure mechanism was not explicitly modeled, however a post-process analysis of the results was performed in order to verify this failure mechanism".

How can I do like him without modeling for shear in short columns??

I have tried the example by Elwood https://opensees.berkeley.edu/wiki/inde ... e_Material but it is not converging.

[marafini.f]

Dear ankurjain1992,

If I do not model Shear Failure in the short columns and directly do the Non-linear time history analysis then how can I get to know abt the shear failure?
I have seen in a paper "Probabilistic estimation of floor response spectra in masonry infilled reinforced concrete building portfolio" by Perrone et al. 2020 where he wrote, "The beams′ and columns′ shear failure mechanism was not explicitly modeled, however a post-process analysis of the results was performed in order to verify this failure mechanism".

In reference to this, if you do not model shear behavior in your model, it means that the response you'll get will not take into account such behavior. If you just need to know for example if your column is failing first in shear or in bending, you can evaluate the strength of your sections with reference to your code of choice and then compare it with the numerical model response in terms of shear stresses. For both mechanisms, you can identify the maximum level of stress for example at the top of the column in shear, and see when it occurs, compared to the maximum level of flexural stress occurring in the midspan of the column. Whichever occurs first is your governing failure mechanisms.

Of course, it is not as simple as that. In RC structures failure can happen for many reasons, diagonal tension, compression, sliding shear, bar buckling, crushing of the toe. If you model with fiber sections you can interrogate stress in different fibers, different materials and extract stress time histories. You will not be able to capture post-peak behaviors if you do not model nonlinearities specific to the mechanisms, but still, you could tell which fiber reaches which level of stress when.

As for the Limit State material, you can read my previous answers to this question in this thread.

I hope this helps.
Enjoy your modelling
Francesca

[ankurjain1992]

Dear Sir,
In the below video at Time 01:05:01, Dr. Petracca has explained how to use ModiMKPinching material to model shear in a column.

#06 Learning Opensees: Nonlinear Modeling of RC (Frame + Shear Wall) Structure (Distributed Plasticity) - REPLY
https://www.youtube.com/watch?v=Erdzh6fJRA8

How to get the parameter for ModiMKPinching is not clear in the video. If possible can you help me how to get those values in the strong and weak directions of the column? Any document related to the calculation will be fine.

Thank you in advance.

[Clarabella]

There is a lot of published literature:
https://www.researchgate.net/publicatio ... e_Analysis
https://www.researchgate.net/publicatio ... nce_models

Start from here, but there are a lot of papers with MK

Regards