Disproportionate Collapse Vulnerability of Cold-formed Steel Storage Racks

Steel storage racks, essential components of industrial logistics systems, are lightweight yet highly stressed structures composed of thin-walled cold-formed steel members. Their susceptibility to progressive collapse stems from local instabilities, semi-rigid joint behavior, and limited ductility, all of which may trigger chain-like failure propagation under exceptional loads. This research, developed within the framework of the PC-RACKS project funded by the Italian Ministry of University and Research, investigates the collapse mechanisms of braced pallet rack systems through a combined experimental and numerical approach. Full-scale tests were carried out on typical beam-to-upright and base-plate connections to evaluate their cyclic response and strength under coupled bending and axial loads. The experimental outcomes were used to calibrate detailed finite element (FE) models developed in ABAQUS, incorporating contact nonlinearities, geometric imperfections, and local buckling effects. A representative five-story industrial rack was analyzed under column removal scenarios using both nonlinear static (pushdown) and dynamic procedures to assess the load redistribution capacity and the influence of bracing configuration. The results emphasize the critical role of connection detailing and bracing systems in preventing disproportionate collapse. The study demonstrates the potential of performance-based assessment procedures that explicitly consider joint ductility, local instability, and dynamic amplification effects. Moreover, it can contribute to the development of refined design criteria and resilience-oriented strategies for steel storage racks, aiming to enhance their robustness and safety under accidental or abnormal loading conditions.