Elastomeric Bearings

[obsadan]

i would like to model bridge elastomeric bearings with SeismoStruct which have elastic stiffness and a displacement limit where after displacement remains constant but the load is transferred to the next element. If linear elastic link is chosen i can not limit the displacements, if the gap-hook link is chosen i can not give a stiffness to the initial part. If i use both links at the same time then maximum tolerance is reached and i can not cure it although i increase the maximum tolerance level to higher values. Would you recommend me another option to do that? Thanks a lot

[seismosoft]

Would a bilinear response curve, obviously associated to a link element, not do the trick?

SeismoSoft Support

[obsadan]

Is it possible to assign a post yield hardening ratio greater than 1?

[seismosoft]

No, it is not. If you wish to do this, you may have a go at using a tri-linear curve, assigning a very high value (but very low displacement) for the first branch (e.g. k0=1e12, d1=0), and then calibrating the other two parameters as needed.

We are not sure, however, that this will serve fully your purposes, given the particular characteristics of high-damping elastomeric bearings response.

SeismoSoft Support

[obsadan]

Sorry for disturbing again. I finally managed to model elastomeric bearing with a linear symmetric + gap/hook element. However the problem turns out to be now that after reaching the defined gap displacement in one direction there is a lock and the displacement does not change sign with the opposite sign cycle. Is there a way to cancel this lock?

[seismosoft]

Not a problem. We are happy to hear that you have managed to (at least partially) solve the problem.
We are not sure we now follow completely your new question, however, hence please do send us your model file, so that we may try to understand better the apparent difficulties, and thus assist you as requested.

SeismoSoft Support

[kotrotsou_e]

Dear Seismosoft,
I want to model elastomeric isolators using linear symmetric curve, with equivalent horizontal stiffness 750kN/m and 10% equivalent viscous damping, but I am not sure how to input the damping, i.e. how to calculate the stiffness parameter. In the manual you propose T#958;/#960;. What period do I use for the isolator? Thank you!
Regards

[ruipinho]

Hi kotrotsou_e,

If you really do need to adopt the mentioned 'linear response curve coupled with viscous damping' modelling strategy (personally, I would instead use directly a bilinear response curve), then you may estimate the required equivalent viscous damping by considering the following relationship:

Damping_Coefficient = Energy_Dissipated_in_Full_Response_Cycle_of_Isolator / (4 * Pi * Energy_Dissipated_by_Equivalent_Linear_Response)

or, in other words,

Damping_Coefficient = Area_of_Isolator's_Full_Cycle / (4 * Pi * Area_of_Triangle_Defined_by_MaxDisplacement_and_MaxForce_in_Isolator's_Full_Cycle)

If interested, you will find more details in a Structural Dynamics textbook, or the subject literature in general.

Best,

Rui