rotSpring2D drift recorder

[JaCl]

Hello.
I am doing an analysis with a plane frame structure using the concentrated plasticity approach. Therefore I modeled the plastic hinges at the girders ends by zero-length rotational springs: rotSpring2D.
To recorder the difference in the rotations at the left and right end of the spring, I used the following recorder:
"recorder EnvelopeDrift -file $Folder/nodeDriftEnv.txt -iNode $list_drift_1 -jNode $list_drift_2 -dof 3 -perpDirn 3"

Then I got a problem, because what should I take as -perpDirn? Since it is a zero-length Element, all the relative distances between the nodes are zero (dir 1, dir 2).

I have tested the file with other recorders, it works fine. Also with the envelopeDrift recorder, but using nodes which do not have the same coordinates.

I suppose there is an (easy) way to get the envelope relative rotation (drift) of the rotational spring, without recordering the rotations at each time step and calculating the difference afterwards.
Can anybody help me with this problem?

I would be glad for some helpful comments.

Thanks a lot,
Clemens

[vesna]

as far as I know, there is no way of recording a drift between the points with the same coordinates. You will have to write small matlab script to get the data you need.

[JaCl]

Hello, thanks for the answer.

That means, that I have to do a "recorder Node" for each of the two nodes, recordering the "displacement" in the third direction (=rotations).
After finishing the OpenSees calculation I have to take the data, subtract one from the other (for each time step) and find the maximum or minimum afterwards. Am I right?

But what if I want to abort the OpenSees calculation, if a certain plastic drift is reached (which is nothing else than the drift of the both nodes of the rotational spring in third direction). I want to have the maximum drift immidiately after each step of the IDA. I think it is a bit complicate (and time consuming) to write out the data in a file, read it in in OpenSees, calculate the maximum drift and delete the outputfiles afterwards - for each plastic hinge!

Is there no way out?

Thanks, Clemens

[vesna]

I do not know of an easier way of doing it.