what's the diffence between rubber isolator and sliding isolator

[shbi]

I am trying to model a bridge slab's friction effect. Can some one tell me how to use link element, espically for rubber isolator and sliding isolator?
Thanks!

 

[Qshake]

I don't know about the particular program but knowing matrix analysis and finite element analysis should provide you with an idea.

The link, like any other element stored in a program like SAP2000 has degrees of freedom associated with each end. For three dimensional analysis you'll get the full six degrees of freedom for each node (end of the element). That is, three translational degrees of freedom and three rotational degrees of freedom.

These degrees of freedom may be expressed in terms of the specific bearing properties. For example, the rubber bearing will typical deform due largely to low shear stiffness properties but will also experience some rotational deformation as well. In many cases, the rubber is supplemented with a lead core to help increase shear stiffness and to some less extent rotational stiffness. AASHTO provides a good reference to determine rubber bearing properties. Of course, rubber's stiffness is also a function of temperature and grade of rubber. So these factors must be taken into account also.

Sliding bearings are similar in that they will have six DOF at each node but the stiffnesses are somewhat different. For example, these bearings have a shear stiffness that is limited by the frictional force resulting from the bridge's normal force (reaction) acting on the smooth surface of the sliding bearing. Typically this is PTFE and it has a coefficient of friction somewhere around 0.08. Once the applied lateral force exceeds this 0.08 times the normal reaction the bearing surfaces will move and no more stiffness is allowed. The bearing will still have rotational stiffness and vertical stiffness.

Regards.

Regards,
Qshake

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