Dashpots are not considered in the solution of the generalized eigenvalue problem

Kx = \lambda M x

The quadratic eigenvalue problem

(\lambda^2 M + \lambda C + K)x = 0

consider damping effects, though.

Can you share your Abaqus model (.inp)?

Dear Mathias D, according to Abaqus manual, element damping is not available for the random response analysis (see tables 1 and 2 https://abaqus-docs.mit.edu/2017/English/SIMACAEANLRefMap/simaanl-c-dynamicproc.htm#simaanl-c-dynamicproc-linear__simaanl-c-alineardynamics-simdamping)