Design of a self centering seismic base isolator for an antiquity

A study of a base isolator implemented to reduce the risk of seismic damage to an ancient Greek Panathenaic Amphora in the collections of the J. Paul Getty Villa Museum is presented. The museum is located in Malibu, California. The seismicity of the area was assessed through a complete Probabilistic Seismic Hazard Analysis that resulted in hazard spectra for a return period of 475 years and a suite of seven, site suitable ground motions. The isolator consists of three metal frames and two sets of compression springs. The metal frames slide on the two interfaces between them implementing the concept of base isolation. The relative displacement of the frames is resisted by compression springs which provide the restoring force. The design incorporated geometric restrictions due to aesthetic concerns, and addressed the structural properties by treating the isolator as a Single Degree of Freedom structure. The achieved period and actual damping coefficient were verified with in situ free vibration tests, used to assess and optimize the design. For the final design, the selected ground motions, appropriately scaled, were used to obtain sets of springs that reduce the seismic response in terms of force and displacement demand.