The uplift of existing buildings to install base isolation systems: challenges and benefits

The use of base isolation for existing structures, especially those employing reinforced concrete (RC) frames and traditional masonry buildings, may pose a number of problems with respect to the installation of the isolation devices. In RC framed buildings, the columns are often cut and partially replaced by either isolation devices or a combination of isolators and sliders. For masonry structures, the installation of isolators at the base of bearing walls appear rather challenging especially whenever the building has also an historical value or when the walls exhibit high slenderness, as for examples in churches or monumental buildings. Historical buildings, museums, churches may, indeed, possess fragile structural and non structural components along with building contents; thus the preservation of such components is of paramount importance during retrofitting interventions, as for example installation of base isolation devices at the base of the structural system. For such structures is essential a prior investigation of the historical analysis with respect to the architectural and urban contexts. Thus, it is possible to highlight the evolution of the building through the historical cartography and analysis of documentary sources (archival and iconographic) to prepare for a possible and correct intervention. The present paper illustrates a patented system that has already been tested on a number of applications, especially in Italy, and may be used efficiently in a number of application world-wide to uplift the building as a whole. Such technique appears reliable, relatively fast and cost-effective to reduce the strengthening of the superstructure. A step-by-step description of the standardised procedure used to uplift the structure is illustrated in a detailed manner. The challenges and benefits of the techniques are presented; critical issues of the procedure are also discussed and possible improvements are suggested. Two case studies of the application of such technique are presented in a companion paper