PSI - Issue 44

Agnese Natali et al. / Procedia Structural Integrity 44 (2023) 2326–2333 Agnese Natali, Francesco Morelli / Structural Integrity Procedia 00 (2022) 000–000

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1. Introduction Automated Rack Supported Warehouses (ARSWs) are buildings specifically developed to maximize goods storage, where steel racks constitute the pallet storage system and, at the same time, the structure of the warehouse (Tsarpalis et al., 2022). To date, no specific design rules or codes are available for their design, and Eurocodes or technical regulations for racks are adopted although often resulting in unsafe design or poor performance (Natali et al., 2022a, 2022b). The lack of dedicated design rules is especially felt in seismic applications, as highlighted by local damage and collapses happened after seismic events (Natali et al., 2022c). Indeed, although this structural system is relatively new compared to the traditional steel structures, very little effort has been put into the development of a seismic design guideline for them (Haque and Alam, 2015). In this framework, possible solutions for dissipative seismic-resistant ARSWs are evaluated, also looking at existing or scientifically based ones for similar structural types (Braconi et al, 2015, Morelli et al, 2016, 2019, Caprili et al, 2022). After a deep analysis around the actual performances and structural typical characteristic of such structures (Natali et al, 2022d), a new design approach named the “Plastic Ovalization admitted Strategy” (POS) is developed, which allows the bearing strength to be exceeded in the diagonal-to-upright connection leading to plastic ovalization of the bolt holes in the diagonal, but not the upright. The diagonal is designed to sustain the plastic ovalization of the hole but preventing bolt shear or buckling through overstrength design rules. All the other elements (uprights and beams) are designed to be over-resistant with respect to the diagonal-to-upright connection. This method can be applied to different structural types (X tension only diagonals and K tension-compression diagonals) and takes advantages of the limited value of the bearing resistance of the connection, which becomes the component that assures the displacement capacity required. To evaluate the performance and applicability of the POS, the cross-aisle frame of both double depth and multi depth structures are examined (these are the main structural typologies for ARSWs). In this paper, the numerical analyses on the evaluation of the performance of the double-depth case study structure designed by applying the POS rules are shown, together with the experimental validation of the behavior of Fig. 1 shows the global configuration of the double-depth case study structure, which is designed according to the POS design rules. The core of the approach is the design of the diagonal-to-upright connections, that should ensure the occurrence of bearing failure before any other failure mechanism involving the connection and the elements by adopting the rules expressed in eq. 1 to 4. These hierarchy rules guarantee that the shear resistance of bolts , , the bearing resistance of the upright , , , the net resistance of the connection zone , , and the buckling resistance of the diagonal , are at least 20% higher than the bearing resistance of the connection (diagonal side) , , . All the other rules guarantee the over resistance of the other elements and of the base connections, and are defined accordingly to the Eurocodes rules for non-dissipative elements ( EN 1998-1:2004: Eurocode 8: Design of structures for earthquake resistance – Part 1: General rules, seismic actions and rules for buildings. , 2004), with slight modifications to meet the ARSWs’ structural needs and peculiarities. ≥ · ℎ · (1) , , ≥ 1.20 ∙ , , (2) , ≥ 1.20 ∙ , , (3) , ≥ 1.20 ∙ , , (4) After the design, the assessment of the performance of the structure is made by performing a multi-stripe analysis (Jalayer and Cornell, 2009) using 30 natural records from the NGA-West2 database (Bozorgnia et al., 2014) and coherent with the design seismic input. The records are scaled to six IM levels that correspond to 60%, 30%, 20%, 10%, 5%, and 3% in 50 years probability of exceedance. The OpenSees (Mazzoni, 2017) open-source software is used for the assessment. To reduce the number of elements and degrees of freedom, the model is upright-to-diagonal connections, which drives the performance of the whole structure. 2. Numerical performance assessment of a case study designed with the POS