Down-Aisle Seismic Behavior of Pallet-Rack Systems: Experimental Tests and Numerical Analyses

Storage-racking systems are cold-formed steel structures made by thin-walled pierced profiles connected through slot-in unbolted connections. They exhibit an atypical structural behavior if compared with standard steel structures and, in the last decades, storage-racks were reported to undergo several collapses due to earthquakes. While in the cross-aisle direction diagonal bracing is easily possible, in the down-aisle direction pallet-rack systems behave like frame structures. As the thin-walled uprights are incapable of plastic behavior, post-elastic resources are only due to the beam-to-column connections. Due to the peculiarity of these systems, experimental analyses are crucial for their correct design. We present the results of a full-scale down-aisle pushover experimental campaign and its numerical extension to nonlinear cyclic and dynamic regimes. In the numerical models, the failure criterion for the uprights and the nonlinear response of the beam-to-column connections are derived by specific experimental tests. The displacement capacity is mostly governed by the fragile failure of the uprights undergoing compression and bending. Due to the particular cyclic response, dynamic simulations show that the displacement demand recommended by standard nonlinear static procedures of building codes is not on the safety side. Overall, properly designed structures are shown to be able to withstand the seismic action.