Using Pinching4 but the result is strange

[Wenyu]

Dear researcher，
I used pinching4 and shell element to build a model for low cycle test simulation. But the result is strange，there is not a cycle，is more like a line. The result curve is shown in the picture below. Can you help me see where the model is problematic

[STKO Team]

I don't really know what you are trying to do here.

The ShellANDeS is a Linear Elastic Shell Element. Even if you assign a physical property, it does not take it into account (in fact you specify E, poission and thickness directly in the Element Property).

Even if you use another shell element like the ASDShellQ4, you can't assign a beam fiber section to a shell. Please check our webinar on how to model walls (we have webinar about shear walls and masonry)

[Wenyu]

I don't really know what you are trying to do here.

The ShellANDeS is a Linear Elastic Shell Element. Even if you assign a physical property, it does not take it into account (in fact you specify E, poission and thickness directly in the Element Property).

Even if you use another shell element like the ASDShellQ4, you can't assign a beam fiber section to a shell. Please check our webinar on how to model walls (we have webinar about shear walls and masonry)

I want to use shell element and pinching4material to build a wall model. It seems that I still do not understand the principle, thank you very much, I will try to modify the model

[ValentinaSB]

Ok, let us know if you have troubles

Best, Valentina

[Wenyu]

Ok, let us know if you have troubles

Best, Valentina

Sorry! I have question again. I want to do a simulation of cyclic loading by using Pinching4 material, and i saw a paper, he used this material and fiber section and beam element, so i try this way, but the result also like a line. There must be many mistakes in my model. Can you give me some suggestions to modify this mode?

[STKO Team]

You are using the Pinching4 material in a Fiber section.
This means that it should be a stress-strain relation.
But looking at the values it does not seem so... the first yielding strain is > 2... it will never go non-linear

[Wenyu]

You are using the Pinching4 material in a Fiber section.
This means that it should be a stress-strain relation.
But looking at the values it does not seem so... the first yielding strain is > 2... it will never go non-linear

Thank for you answer. I also realized this problem. So if i want use the force-displacement number,i need change the unit to kN and m?I make some change, but the software operation is very slow and shows 'failed to get compatible element forces & deformations for element', is there something wrong?

[STKO Team]

It's not about the unit... The uniaxial material in OpenSees can be used for multiple purposes.
Depending on what physical behavior you want to represent.
If you put it inside a fiber section, then it should be a stress-strain curve, not a force-displacement.
Could you please explain what your pinching4 is actually representing?

[Wenyu]

It's not about the unit... The uniaxial material in OpenSees can be used for multiple purposes.
Depending on what physical behavior you want to represent.
If you put it inside a fiber section, then it should be a stress-strain curve, not a force-displacement.
Could you please explain what your pinching4 is actually representing?

i used the pinching4 to represent the skeleton curve of the shearwall.

[STKO Team]

You should use it in a section aggregator to represent the shear behaviour of the shear wall, while the fiber section should represent the bending behavior.

You should have a look at our beginner webinars. The last one explains this:
https://asdea.eu/software/get-started-webinars/
3D Frame Structures (Part 3) - Masonry: EFM of trilite and masonry walls