Esposito, Francesco (2024) Design procedure for Intermediate Isolation Systems (IIS): application for existing building retrofit. [Tesi di dottorato]

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Abstract

In this thesis work, the vibration control strategy of intermediate isolation system (IIS) is investigated. Such system has special dynamic characteristics: the structure above the isolation system (US) can function as a huge mass damper for the structure below the isolation system (LS). Due to this type of dynamic behaviour, IIS has become very widespread and popular in Japan, where specific guidance for the design of buildings with IIS can be found in the national standards. On the other hand, in Europe, IIS is almost completely unknown, although it is an ideal solution when intervening on existing buildings located within major urban centres in medium or high seismic risk zones. In fact, IIS can be achieved by placing an isolated structure on the roof of existing buildings, thus simultaneously increasing the volume of the building, and reducing, or at most not increasing, the seismic demand in the existing building. Therefore, to facilitate the deployment and application of the IIS for the extension and seismic retrofitting of existing buildings, a detailed design procedure divided into 5-block is defined in this thesis. The key tool of the whole design procedure is the IIS design spectrum, derived by means of parametric response spectrum analysis (RSA), allows to predict the maximum seismic response of the lower structure (LS) as the isolation period varies. Thus, it allows to identify the design solution that maximises the mass-damping effect on the LS. The design procedure is first applied to a real case study for evaluating the effectiveness of IIS working as a nonconventional Tuned Mass Damper (TMD) for the existing construction and then applied to several case studies to verify the accuracy of the response prediction offered by the IIS design spectra. In the latter case, it is shown that the IIS design spectra can also be used when the existing building exhibits inelastic behaviour. However, in this case, a stepwise procedure should be followed, which leads to the definition of a so-called inelastic behaviour zone for IIS, bounded by two IIS design spectra. Finally, a closed-form relationship based on the application of the pole allocation method is proposed as an alternative to the parametric RSA for deriving the IIS design spectra.

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