Do you mean rolling bearings ? If so, the stiffnesses are non-linear. You may also need gap elements depending on the problem. There are at most three overall stiffnesses per bearing - axial, radial and tilt. You can either compute them from scratch, (in which case you must know the race curvatures if they are ball bearings, and the theory - its pretty complicated - elliptic integrals and simultaneous Newton Raphson equation solution etc), or get the curves from the manufacturers, or use available software. Poplawski has developed an FEA interactive version of his COBRA bearing program, which will also do structural/thermal bearing effects, but I think it only works with ANSYS. Good guy to know on rolling bearings though. If you are talking any other kind of bearings - can't help.
