Optimization and Effectiveness of Load-Level Isolation System (LLIS) for Steel Pallet Racks

Recent Italian earthquakes have revealed the high seismic vulnerability of industrial steel pallet racks. To mitigate this risk and enhance the structural performance of the racks, some mitigation systems have been proposed, based on specific base-isolation or dissipation devices. In this framework, this study explores an innovative control system for dynamic actions on steel pallet racks, known as the Load-Level Isolation System (LLIS). The LLIS utilises stored pallet masses as tuned mass dampers, by inserting isolators between the pallet and the load level. Specifically, the paper presents a general design procedure for the LLIS, considering as design variables the isolated mass amount, the LLIS position within the rack, and the primary dynamic characteristics of the rack. Then, to assess the effectiveness of the LLIS in reducing seismic effects, a case study pallet rack is modelled and analysed in Time-History, with and without the LLIS in various positions. The results demonstrated substantial reductions in the cross-aisle displacements and axial forces of the uprights, as well as a decrease in cross-aisle pallet accelerations.