PSI - Issue 78

Alessandro Mei et al. / Procedia Structural Integrity 78 (2026) 120–127

121

1. Introduction Industrial pallet racks are thin-walled structures made of cold-formed steel (CFS). Their light weight, ease of assembly, and modularity have made them quite common in the logistics chain. They consist of vertical elements (“uprights”) and horizontal elements (“pallet beams”) , typically connected by boltless joints. Uprights are paired in the cross- aisle direction with bracings (this assembly is often called “frame”), while in the down -aisle direction, usually there are no bracing elements to avoid obstructing the handling of goods, as outlined by Dai et al. (2018). Therefore, these structures have two different resisting schemes: in the cross-aisle they behave as trusses, while in the down-aisle direction behave similarly to MRFs, being their stability in this plane provided by the stiffness and capacity of the upright-to-beam joints as described in Bajoria et al. (2010) and Mei et al. (2021). In recent years, seismic design has undergone a substantial revision, with the introduction of innovative technologies and techniques to retrofit historical and industrial buildings. However, logistics facilities and racking systems have received less interest from the point of view of seismic retrofit, essentially because research has traditionally focused on characterizing the structural behaviour of individual components (uprights, beams, joints) and entire rack assemblies through experimental and numerical testing. The stability of uprights was investigated by Baldassino et al. (2019), Bernuzzi et al. (2014), Bertocci et al. (2017), Orlando et al. (2017), the behaviour of upright to-beam joints by Gusella et al. (2018), Mei et al. (2022), Zhao et al. (2014), the global behaviour of steel racks by Bernuzzi et al. (2017), Kanyilmaz et al. (2016), Sena Cardoso & Rasmussen (2016), and advanced seismic protection techniques by Kilar et al. (2011), Mei et al. (2023). Only recently, thanks to the introduction of new regulations and a growing awareness on the part of end users, a paradigm shift occurred . “Guidelines for the design, execution, verification and safety of rack structures” by C. S. LL. PP. (2023) have placed explicit emphasis on the need to assess seismic vulnerability and promote retrofit interventions for existing rack structures, and also in the academic community the first research has been developed by Donà et al. (2024) and Mucedero et al. (2025), who studied rack vulnerabilities and determined fragility curves. Within this emerging framework, the present research addresses the seismic assessment and strengthening of existing steel pallet racking systems. Specifically, the study proposes a set of local strengthening strategies applied to the upright-to-beam joints of an existing steel racking system to improve its longitudinal behavior and energy dissipation capacity. The present paper reports the preliminary outcomes of the research project “SAVE -RackS ” funded by the Tuscany Region, which is composed of experimental tests on rack joints and assemblies together with finite element modelling. The upright-to-to beam joint here presented is a semi-rigid joint made by a pallet beam with a 130/45/1.2 (height/ M12base/thickness, referred to as A1345M) tubular section and a cold-formed perforated upright with a U-section (“130U”) and a thickness of 2.5 mm. Welded to the beam along three sides, there is a 5-tab connector of 3 mm thickness. It is worth noting that, although the pallet beam resembles a tubular beam, it has a closed built-up CFS section, formed by the coupling of two open C-shaped profiles that interlock and are both welded to the end connectors. The choice of considering built-up profiles for beams in this study derives from their widespread use and recurring presence in existing racking systems. Fig. 1 shows the geometry of the joints. In the load transfer mechanism of the beam-column bending moment, the tensile force is carried by the tabs, while the compression force is transferred through direct contact between the beam-end connector and the column flange. In all the tested joints, a safety clip prevents the connector from disengaging from the upright due to accidental impacts. The following steel grades are used for the elements of tested joints: S350GD (f yk = 350 N/mm 2 ) for uprights, S355MC (f yk = 355 N/mm 2 ) for beams, and S355JR for connectors (f yk = 355 N/mm 2 ) for connectors. 2. Experimental campaign 2.1. Upright-to-beam joint