plastic chord rotations of reinforced concrete members

[miranc]

Hi,
I'm trying to capture the formation of plastic hinges in my structure. All members are reinforced concrete. I am using forceBeamColumn elements. I first tried to capture one beam (tag number 74) which I know will yield first (computed in another program). I have performed a displacment-controlled pushover analysis, and recorded the element with the follwing command:
"recorder Element -file PlasticHinge.out -time -ele 74 plasticDeformation;"
What happens is that I get non-zero values in all the steps which is clearly wrong.

Is it even possible to use "plasticDeformation" for RC members?

Some posts in the forum suggest that this command is only valid for materials that have constant E-moduls upp till yielding, e.g. steel.

Does anyone have any suggestions on how to record plastic rotations for RC members ?

[fmk]

the plastic rotation by definition is simply the current rotation minus the elastic component (for force beam column the elastic rotation is determined by simply dividing the current end forces divided by the initial tangent in a matrix sense). This is not an OpenSees definition but one used in mechanics: http://en.wikipedia.org/wiki/Plasticity_%28physics%29

your problem is that it makes no sense when using an RC model for which ANY deformation, even the slightest strain, results in "plastic deformation" as opposed to a steel model. This is why you see plastic deformations at every step in your analysis. It is not wrong, it is a consequence of your material.

[miranc]

Thank you very much for a quick reply in all my posts. I'm writing a masters thesis and have just begun to use OpenSees. This forum has been extremely helpful.