DEVELOPMENT AND VALIDATION OF A SEISMIC ISOLATION SYSTEM FOR LIGHTWEIGHT RESIDENTIAL CONSTRUCTION
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While seismic isolation has found widespread application ranging from apartment buildings to monumental and essential facilities, only Japan has a significant number of applications of seismic isolation to houses, which after some 5000 applications has reached a halt. The high cost of highly engineered seismic isolation systems is most likely the reason for the lack of applications other than in Japan. There is an interest to develop practical, simple and reliable seismic isolation system for houses, which can be easily manufactured in most countries without the requirement for advanced technological capability. The work presented in this report concentrates on the development, construction, testing, modeling and validation of an isolator with these characteristics. Moreover, the work concentrates on the development and validation of design procedures for reinforced concrete houses equipped with this isolation system in areas of high seismic hazard in Turkey. The developed isolator is a single concave rolling isolator cast in fiber and steel-reinforced high strength concrete with a rolling ball made of urethane (Adiprene) in hardness of 95A or 62D and reinforced with a core of steel. The isolator also features a displacement-restraint system to prevent collapse of the isolator at large displacements. For applications anywhere in Turkey, the isolator has an ultimate displacement capacity of about 650mm. The isolator was built and tested to determine its properties, including creep and lateral force-displacement characteristics. It was observed that the isolator exhibits significant rolling friction that is practically independent of the hardness of the rolling ball and the conditions of loading and motion. It also exhibits a post-elastic stiffness and an effective yield displacement that are much larger than those predicted by models assuming rigid rolling ball behavior. These properties are desirable and emanate from the viscoelastic behavior of the rolling ball. Models of behavior of the tested isolator were developed and validated for response-history analysis in programs OpenSees and SAP2000. Moreover, an advanced computational mechanics-based model was developed that was capable to predict the observed features of rolling friction, increased stiffness and large yield displacement.A parametric study of the collapse performance of two-story houses with a range of properties in areas of high seismic hazard in Turkey was performed following the procedures of FEMA P695 with due consideration of spectral shape and vertical ground motion effects. It has been shown that houses in Turkey designed by the recommended procedures and using the developed isolator have an acceptable collapse risk described by a probability of collapse that is less than 10% given the occurrence of an earthquake characterized by a 2475-year return period earthquake, whereas comparable non-isolated houses designed to meet the criteria of the applicable codes in Turkey do not.