Vertical seismic isolation systems for new and existing structures in process and nuclear power plants

This study introduces innovative vertical isolation systems, the so-called Negative-Stiffness Based Vertical ISolators (NVISs). The NVISs integrate post-tensioned cables and mechanical amplifying mechanisms to overcome buckling limitations of traditional compression-based negative stiffness isolators, offering a lightweight, tunable solution with extended negative stiffness regions. NVISs retrofitting capabilities, which do not require column cuts, facilitate practical seismic upgrades, addressing critical gaps in vertical isolation of large-scale structures. Unlike prior studies focused on small-scale applications, this work emphasises realistic applications on heavy structures. Along these lines, analytical models and dynamic analyses including friction were developed and carried out to characterise their behaviour. Small-scale experimental validation was conducted using additive manufacturing and a shake table to simulate dynamic loading conditions. Then, two realistic case studies were considered: (i) the integration of NVIS devices into the columns of a Small Modular Reactor (SMR) building; and (ii) the use of a combined horizontal–vertical isolation system composed of NVIS with horizontal rolling isolators for the protection of a spherical propylene tank in a petrochemical facility, evaluated by means of nonlinear Coupled Eulerian–Lagrangian (CEL) time-history analyses. Relevant results demonstrate more than 60% vertical seismic force reduction across diverse applications, highlighting the system’s adaptability for both new and existing industrial, nuclear, and critical infrastructures.