Faiella, Diana (2017) The Intermediate Isolation System for new and existing buildings: seismic behavior and design criteria. [Tesi di dottorato]

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Seismic isolation is nowadays a mature technology in the field of civil engineering, appreciated for its conceptual simplicity and its effectiveness in mitigating the seismic actions on structures. After decades of applications, in which isolated buildings have exhibited excellent seismic behavior even during major earthquakes, the base isolation system (BIS) technology is today widespread and popular all over the world, representing a valid option for structural designers to ensure superior seismic performance to new buildings or in order to retrofit existing ones. Throughout the years, architectural needs pushed the limits of the isolation technology in search for new structural configurations. Amongst the structural technologies deriving from the base isolation concept, intermediate isolation represents one of the most interesting. The Intermediate Isolation System (IIS, also appointed as mid-story or inter-story isolation) is a very actual topic and it is currently spreading and gaining significant popularity, mainly in Japan. Advantages of the IIS system include a remarkable architectural flexibility (different functions and, as a consequence, different structural systems are allowed for upper and lower structures) and the applicability for high-rise buildings. In some cases, an elevation with inter-story isolation has been proved to serve as a valid retrofit strategy for existing buildings, avoiding massive retrofit interventions in the lower structure and disruption of the hosted activities. However, while the design concept of base isolation is today highly mature and several thousands of applications have been realized, for the IIS not a single, fully shared design approach is defined, but multiple approaches. The overview of the main scientific contributions on this topic provided in the inherent literature reflects the variety of approaches, both in the formulation of the problem and in the definition of the design objectives and parameters. Basically, three major conceptual approaches can be clearly identified, each mainly focusing on one single aspect of the three ones related to IIS, namely: energy dissipation, isolation, mass damping. In this context, the aim of the present thesis is to explore the actual and potential applications of IIS, by identifying the predominant role among the three behavioral aspects, and by defining design criteria for benefit from all these aspects. In a first step of research the analysis of two real building case-studies representative of the wide IIS applicability, has been carried out, in order to interpret the latest design practice in the light of approaches and indications coming from the world of research. Hence, starting from the precious outcomes of the analyses, two parametric analyses have been carried out, considering both new and existing buildings. In the first parametric analysis, developed on 1D-MDOF inter-story isolated models, the influence of different locations of the isolation system along the building height, and of different mass and stiffness distributions, has been investigated. In the second parametric analysis, carried out on 1D-3DOF inter-story isolated models, the response of an IIS vertical addition for retrofitting an existing masonry building, has been investigated, with the aim of identifying the optimal isolated superstructure configuration; then, a 3D FEM model is adopted for the detailed analysis of the IIS structure.

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