Investigation of new mixtures based on natural rubber and nitrile-butadiene rubber for high damping base isolation systems

High damping rubber isolators (HDRBs), which are popular in base isolation systems, extend the natural vibration periods of structures and increase the energy dissipation capacity of the systems. Thus, they can protect structures from damage that may occur in earthquakes. The difference between HDRBs and other elastomer bearings is the chemical formulation of the rubber used. The aim of this study is to prepare a new rubber mixture that is resistant to seismic loads and has good damping properties for HDRBs. In this direction, rubber mixtures were prepared with three different formulations. The mixture of ingredients used in this study is Natural Rubber (NR), Nitrile Butadiene Rubber (NBR), Carbon Black (CB), process oil, Zinc Oxide (ZnO), Stearic Acid (StA), coumaron resin, protective agent, sulfur and accelerators. Quadruple shear block specimens were produced with elastomers produced with mixtures. Dynamic tests were performed on these samples. Elastomer earthquake isolation bearings with a damping ratio of 6% or greater are classified as 'highly damped'. In this study, values greater than 10% were obtained for damping ratio values at 100% shear stresses. Experimental and numerical analyses revealed that the damping values of the compounds developed with NBR-based formulations are at an acceptable level for highly damped isolators. In general, it was observed that the damping properties increased from 6% to 12%. Therefore, it is thought that the developed HDRB compounds can be used as elastomers in the construction of seismic isolators with high damping properties.