No “Pinching Effect” in Bilin material?

[burnningcat]

Dear Sir,

I use the example of a rotational spring that uses Bilin material in the OpenSees website:
http://opensees.berkeley.edu/community/ ... =2&t=30954

But no matter how I change the parameter of Bilin material, I can not get any “pinching effect” as describe in the Author of this material, as in the paper in also in the OpenSees Website:
“Hysteretic models that incorporate strength and stiness deterioration” by Luis F. Ibarra; Ricardo A. Medina and Helmut Krawinkler. EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS Earthquake Engng Struct. Dyn. 2005; 34:1489–1511

In this paper, the Author states very clearly that this material has the “Pinching Effect”, which means the Unloading stiffness will reduce when the Resisting Force unloads to the zero value. And then the stiffness will increase again when it reach the “Reloaidng branch” in the other direction. Also the in Figure 9 of this paper, the Author shows 4 simulations results, all have the pinching effect.

In the OpenSees model, the parameters are:

Lamda S; # basic strength deterioration
Lamda K # unloading stiffness deterioration
Lamda A # accelerated reloading stiffness deterioration
Lamda D # post-capping strength deterioration

I have play with these parameters(Also with the corresponding exponent parameter for deterioration,like cs, ck, ca, cd). But I find that it is not related to the “Pinching Effect”. And I just can not get any “pinching effect” as describe in the paper.

So I kindly ask if somebody can tell me, if there is the “pinching effect” in the Bilin material? Or if someone can give an example of how to get this “pinching effect”? Thank you very much in advance!

[vesna]

Yes in the example I provided I did not include pinching effect.

I will contact the author of the material and ask him to post an example with a pinching effect.

[vesna]

I contacted the author of the material and he told me that as of now pinching effect can not be captured with the current version of this material. However, he is developing a new material that will account for pinching effect.