Variability of dynamic properties of rubber compounds for elastomeric bearings

The λ-factors for stifness and damping of rubber bearings should be experimentally assessed during the qualifcation process or deduced from tests performed on material specimens. Moreover, the λ-factors suggested in the informative annexes of EN 15129 and of EC8-part 2 can be also used as reference values. However, they are derived from outdated experimental campaigns and do not refer to all the sources of variability. In this paper, a statistical analysis on a signifcant set of rubber compounds, certifed according to EN 15129 from diferent suppliers, is carried out to assess the current variability of the dynamic properties of such compounds. Diferent sources of variability may be identifed by distinguishing between behavioural and environmental effects. For elastomeric bearings, especially high-damping rubber (HDR) ones, the main behavioural effects are strain amplitude, strain rate dependence, and cyclic degradation, whereas the environmental effects are due to temperature variation and ageing. All these sources of variability have been analysed in this paper. The results of the statistical analysis have been used to propose a new set of λ-factors for all the sourced of variability studied. Such new values have been compared with the ones suggested by the codes when available. The main inconsistencies found have been highlighted and commented in this paper. Finally, some considerations about the infuence of such variability on the structural response of base-isolated structures have been drawn by focusing on both the isolation system and the superstructure.