Experimental assessment of elastomer compounds for rubber bearings

The mechanical properties of the elastomers used in the manufacture of seismic rubber isolators are sensitive to mechanical and environmental working conditions, therefore resulting in large variation ranges of the performance of seismic isolation systems installed in buildings and structures. The study investigates the cyclic stress–strain behavior of several elastomer compounds, with design shear moduli covering the range between 0.35 and 1.50 MPa. Tests are carried out on rubber blocks loaded in shear and the influence of several factors on the dynamic properties (secant shear modulus Gsec and equivalent viscous damping ratio ξ) of the compounds is investigated, including strain amplitude, repeated cycling, frequency of loading, air temperature, and application of concurrent shear and normal (compressive) load. The results are analyzed and used to calculate property modification factors of design values for each compound. The variability of the mechanical properties is studied and compared to the requirements on production rubber bearings set in the current European standard on anti-seismic devices.