PSI - Issue 64

Margherita Autiero et al. / Procedia Structural Integrity 64 (2024) 1798–1805 Author name / Structural Integrity Procedia 00 (2019) 000–000

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direction by horizontal beams and by a bracing system to provide lateral stability of the structure in this direction. In the CA direction, all the frames are connected by an upper truss (see Fig. 1a).

13th LOAD LEVEL

LATERAL AISLE

1st LOAD LEVEL

CENTRAL AISLE

III SHOULDER IV

V SHOULDER

I SHOULDER II

LATERAL SHOULDER

LATERAL SHOULDER

(a)

(b)

SHOULDER

SHOULDER

Fig. 1. (a) an ARSW during its construction. (b) cross-aisle direction (Source: ROSSS s.p.a.).

Three building types of ARSW can be defined depending on the pallet disposal: single-depth, double-depth, and multi-depth. In the single-depth configuration, there is one unit load line per frame; in the double-depth configuration, there are two unit loads per frame. In this work, the focus is given to Automated Multi-Depth Shuttle Warehouses (AMSWs), as a specific ARSW type (see Fig1b). AMSWs are compact systems providing large surface occupation and maximum storage density, where the handling of unit loads is realized by a system of shuttles that move goods along rails in the warehouse DA and CA directions. To design ARSW, the reference regulations are EN1993-1-1 and EN1993-1-3 for steel structures and EN1998-1-1 for seismic action. Moreover, the designers usually refer also to specialist regulations such as EN15512 which provides principles for the structural design of pallet racking systems, and EN16681 which indicates principles for the seismic design of pallet racking systems. Hence, while well established principles and rules supported by experimental evidence and theoretical research are available and presented in Bernuzzi et al. (2015) for the usual SR, for the ARSWs, which are systems larger, taller, and more complex than usual SR, manufacturers and designers have questioned the suitability of the available regulations for ARSWs, for years. Recently, in Italy, new guidelines providing a framework in terms of procedures are available for designing, improving, and adapting industrial metal racks in the earthquake zone. ARSWs are characterized, on one hand, by a peculiar structural configuration, that strongly influences global behaviour and, on the other hand, by unique non-standard structural components and connections. Indeed, these structures mainly consist of thin-walled sections obtained by cold-forming thin metal sheets that, on one hand, optimize the structural performance by reducing the steel weight, the costs, and the assembly time. On the other hand, these types of sections are usually classified as class 4 cross-section, according to EN1993-1-1, so they have much lower strength and stiffness than hot-rolled steel members, these members can fail by a variety of buckling modes including global, local, and distortional buckling and their interactions. For this reason, usually, racks are made with channel sections and stiffened with additional folds (called “lip”) to reduce local and distortional buckling phenomena caused by the small thickness of the sections (typically from 1.5 mm to 3.0 mm). However, an ARSW can be characterized even by hollow square sections depending on the dimensions and the requested load. In the last decades, the global structural behaviour of traditional racks has been investigated focusing especially on a seismic point of view. Caprili et al. (2018) investigated the efficiency of Eurocodes’ design and analysis rules for ARSW, in terms of feasibility, structural performance and costs demonstrating how the capacity design requirements for ARSW are challenging to satisfy especially in terms of the maximum difference of the over-strength factor between load levels, requested in the case of X-braces steel-structures. These problems have led designers to consider ARSW as "non-dissipative" structures. Only in recent years capacity design approaches specifically made for ARSWs were proposed (Natali et al. (2022)), defining rules and hierarchies that consider the characteristics of these structural systems. At ambient temperatures, EN1993-1-5 gives two methods to consider the effects of local buckling in the design, i.e., the “effective width method” and the “reduced stress method”, while the distortional buckling strength is considered by using a reduced thickness in the edge stiffener and/or deformed part of the compression flange. The behaviour of thin-walled steel members in centric and eccentric compression and particularly of cold formed steel members (CFS) have been widely investigated by many researchers through experimental tests. Test on fixed-ended cold-formed steel rack-section columns were carried out to investigate