A Comparative Study On The Seismic Response Of Base-Isolated Secondary Systems

Since ancient times earthquakes have resulted in destructive and catastrophic damages due to their unpredictability as a natural hazard. With the increasing development of new technology, more valuable and heavy facilities are housed inside buildings such as hospitals, banks and government agencies. Some of these facilities, called secondary systems, are so vulnerable to seismic damage. Base isolation is an earthquake protection technique which separates a building from the ground to protect the structure with an isolation device. If the main objective of seismic isolation is to protect the secondary systems, using base isolation for secondary systems could be more economical than isolating the whole primary structure in order to reduce the seismic response of secondary systems. Besides, in an existing structure, it is much easier to only isolate the equipment that needs to be protected.In this research, the development and practical application of base isolation are presented and six common types of base isolation systems have been thoroughly studied in the literature and are presented in this report. Each of these systems has its own unique components, mechanical properties, and functional mechanism. Comparison of seismic responses between a base-isolated primary structure and a base-fixed structure is presented. And a comparative study on seismic responses between a fixed secondary system and an isolated secondary system in a non-isolated primary structure is conducted. Then the floor location of the isolated secondary system is changed and the corresponding seismic responses are compared. It is confirmed that the seismic responses of superstructure and the secondary system both can be significantly reduced by applying a suitable base isolator. It is suggested that the secondary system isolated from floor should be placed on the lower floor to have a better performance in seismic response reduction. Based on those findings that confirm a theoretical concept, and given that many secondary systems are housed on higher floors of structures, a secondary system located on the top floor of a three-story primary structure is studied. Four cases are set by combining an isolated or a non-isolated primary system and secondary system. Three kinds of base isolation systems are compared. Numerical simulations are performed and the response spectra of the secondary systems are presented in each case.The comprehensive study carried out in this research confirms the practical effectiveness of base isolators for secondary systems. It also explores the best floor location for isolated secondary systems and the most effective isolation case for a secondary system on higher location, providing a useful guideline for housing secondary systems in structures such as nuclear facilities, hospitals, telecommunication and governing buildings in order to protect valuable equipment.