Result of plastic hinges

[luckypants]

Dear STKO Team：

After I finished my analysis, how could I get the result of plastic hinges?

I create plastic hinge by uniaxialMaterial ModIMKPeakOriented. There is backbone curve and hysteresis loop in this material.

How could I get the data and the result?

Here is my model. Any advices and helps that you provide are highly appreciated.

Best Regards

[Clarabella]

Dear Luckypants (by the way in ASDEA we were wondering why your nickname is luckypants..),

You can go in the post processor and visualize the lumped hinges using the gauss point plot. Remember to select the results you need in the recorder.

Best regards

[luckypants]

Dear STKO Team：

Thank you for your help.( I named my nickname casually . )

But I still can't get the results of plastic hinges by using the gauss point plot.

I don't know why there is no data in gauss point plot like the following picture. I want the data of the backbone curve and hysteresis loop.

By the way, when I checked the displacement and reaction force, the result looks weird. Is there any wrong in my model?

Any advices and helps that you provide are highly appreciated.

Best Regards

[Clarabella]

Dear Luckypants,

your model is incorrect. Attached you can find two files.

ZL+rotation.zip

(128.63 KiB) Downloaded 236 times

: drawing to explain how to fix your model,

ZL+rotation.zip

(128.63 KiB) Downloaded 236 times

: the corrected model using the penalty method.

1) The flexural degree of freedom you need to chose is 5, and not 6. Bare in mind that zerolength uses global axes
2) You fixed the slave nodes (see the diagram):
a) The plastic hinge is not stressed because it is not loaded. This is because you selected the wrong node.
b) The slave nodes are constrained with sp and equal constraints. This cannot be handled by plain constraints, you need to use the penalty method.
To avoid node selection errors we created our automation called Hinged beam. If you still want to create manually the zero length, I suggest you to create it with the nodes disconnected, then select the correct nodes, and only at the end you can make coincide the nodes (if they superimpose you might select the wrong node).

[luckypants]

Dear Clarabella：

Thank you very much. The diagram you drew helped me a lot.

I have known my problems, but I still want to ask some questions.

1. How do you know the flexural degree of freedom is 5?

If zerolength uses global axes, the flexural degree of freedom will be 4(Mx) or 5(My).

Because the acceleration of sine wave I inputted was in X direction, the flexural degree of freedom should be 4. Is it right?

By the way, I have asked similar question here before. You said that the plastic behavior depends on the local axes defined, and in STKO/OpenSees X local axis was always along the longitudinal deirection. That was why I set zerolength in 6 direction (Mx), and the following picture shows the local axes of the column. The flexural degree of freedom is Y local axis (5) and Z local axis (6).

I confused about when I set plastic hinges. Which axes does it depend on ? global axes or local axes?

2. How could I get the data(moment and chord rotation) of backbone curve which I set ?

In addition, I fixed the top of column except for X direction because I want to simulate the experiment which has done by MATS(Multi-Axial Testing System). There is constraint on the top of column.

3. Finally, I create my model by Hinged beam. After I create plastic hinge, the result of node 2 displacement(the top of the column) don't change. It seems the column still be elastic not plastic. Is there any wrong with my model?

Any advices and helps that you provide are highly appreciated.

Best Regards

[STKO Team]

Dear user,

By default the zeroLength element (as any other "interaction" in STKO) uses the global axes, unless you assing a new user-defined localAxes to them.

Then if you model your column drawing the zero-length elements manually, they will use (by default) the global axes, so the bending DOFs of the plastic hinge will coincide with the global rotational DOFs, so 4 (Rx) and 5 (Ry), while 6(Rz) will be the torsional DOF.

If instead you use a HingedBeam element, the zeroLength for the plastic hinges will use the same local axes used by the inner beam element. So in you picture, the local X is alligned with the beam column, while the bending axes are the local Y and local Z. More specifically the local rotational DOF about the local Y axis correspond to the global Ry rotation. While the local rotational DOF about the local Z axis corresponds to the global Rx rotation. So in this case the bending DOFs for your hinges are 5 (Ry) and 6(Rz) because they refer to the local coordinate system of the beam, while 4(Rx) is now the torsional DOF.