Kikuchi Aiken material

[hbma]

Hi,
I have used KikuchAiken material for modelling LRB isolators within the following process:
1)Defining the material(whit the inherental output of force-deformation)
2)Using zerolength element with the above material for two horizontal directions
3)Using zerolength elemnt with a rigid material for vertical direction
The problem is that my model does not converge around seconds when the strong motion of record stars at say 8.5 sec. I guess the problem is due to KikuchiAiken material. when I use too small number for the lead plug shear modulus, the convergence problem is solved, but by increasing it to its real amount, it does not converge. Is there any strain limit defined as default for this material? If so, is this dependent on alpha (Shear modulus of lead plug)?

Sincerely

[KenIshii]

Hi hbma,

KikuchiAikenLRB material has a strain limit of 400% shear strain, and the limit is not dependent on alpha.
If the response exceeds the limit, the material outputs the message "Response value exceeded limited strain".

[hbma]

Can I increase this limit?
Such an error does not appear on the screen, it is a state of suspension, neither an error appears nor it continues the analysis and goes to the next loops.
Ironically, by reducing alpha from 130.e6(si units), which is the true lead shear modulus, to 30.e6, an underestimated lead shear modulus, the convergence is solved.
In the .tcl file in "http://opensees.berkeley.edu/wiki/index ... B_Material", alpha is assumed to be 0.588e6, I do not know why. It is a really small figure for this purpose. Please introduce the probable reference.
BTW, how shear strain is calculated while I have used zerolength element?

Sincerely

[KenIshii]

1) In the KikuchiAikenLRB material, alpha, the apparent shear modulus of the lead plug, is used to calculate the secondary stiffness. For example,
M. Ikenaga, A. Suzuki, M. Miyazaki, "Examples which applied anti-seismic devices to existing buildings and the new approval system for seismic isolator in Japan", 7th International Seminar on Seismic Isolation, Passice Energy Dissipation and Active Control of Vibration of Structures, Assisi, Italy, October 2-5, 2001.
uses 0.588e6 [N/m2] for alpha. The secondary stiffness, Kd, is
Kd = Gr*Ar/Hr + Alph*Ap/Hr

2) The shear strain equals to the deformation (response of the ZeroLength element) divided by Hr (input data of the KikuchiAikenLRB material).

Thanks

[hbma]

Excellent, so many thanks.