Help for Calculation of Stiffness Properties of Elastomeric Bearings

I’m trying to model a bridge in SAP2000. In my model each elastomer is defined in beam support locations one by one. I’m using NNLINK elements for bearings. In defining NNLINK elements SAP2000 require 6 stiffness values (2 for lateral movement, 1 for vertical movement, 1 for torsion and 2 for rotation) and in addition to these, the damping coefficients for each elastomer. The calculation of lateral stiffness is well known (F=G.A/h). But I could not find any formulae for the other 4 stiffness properties (vertical stiffness, rotational stiffnesses and torsional stiffness). I’ve reviewed all of the questions and answers related to elastomeric bearings and I realised that no one has mentioned about the other stiffness properties (vertical, rotational and torsional). That’s why I wonder whether these stiffnesses are important or negligible (entering zero stiffness values) in modelling with NNLINK elements in SAP2000. Does anybody know about the calculation of the vertical, rotational and torsional stiffness values of elastomeric bearings? Cengiz CELIK
Civil Engineer Ms