Design and Testing of High Damping Rubber Earthquake Bearings for Retrofit Project in Armenia
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Isolation of structures from horizontal ground motions is gradually becoming a more common method of providing protection from earthquake damage. By reducing the seismic forces transmitted, isolation protects the contents and secondary structural features as well as the main structure; the safety of occupants and passers-by is thus also enhanced. High damping rubber (HDR) bearings are a simple and economical means of providing isolation. They have the low horizontal stiffness required to give a long vibration period (typically 2s) to the structure when mounted on the bearings. Their vertical stiffness is high, thus minimising any rocking of the structure during an earthquake. The damping needed to limit the displacement of the structure and reduce the response at the isolation frequency is incorporated into the rubber compound so that there is generally no need for auxiliary dissipation devices. The bearings can be designed to withstand safely the large horizontal displacements imposed during an earthquake. The service life of the bearings is expected to be several decades (Fuller & Roberts, 1997), and they should require no maintenance. Many projects throughout the world have installed seismic isolation systems based on HDR bearings. During the 1994 Northridge earthquake in California and the Kobe earthquake of 1995 seismically-isolated buildings performed well.