Base Isolation Design of Steel Structures on Soft Soil

Base Isolation systems have been implemented on civil engineering structures subject to earthquakes worldwide for a number of years because of their simplicity, reliability, and effectiveness; passive isolators usually consist of members located in between the foundations and the super-structure and characterised by high damping capacity and relatively low stiffness. Devices are available typically coupling elements endowed with large translating deformability, mainly aimed at shifting the structural frequency band, with components devoted to dissipate and/or absorb the filtered transmitted energy. Although characterized by stability and low energy demand, BI devices are limited in their ability to adapt themselves to changing demands for structure response reduction. The performance of such devices may fail expectations under special, like in case of soft soil, or unexpected conditions, and, in order to optimize the overall performance of the control system, the isolated system should be embedded in a more complex system able to possibly activate some corrective actions. In the paper, with reference to steel structures, a strategy is outlined to this purpose, devoted to existing, or not, isolated constructions.