PSI - Issue 44

Agnese Natali et al. / Procedia Structural Integrity 44 (2023) 2334–2341 Agnese Natali, Francesco Morelli / Structural Integrity Procedia 00 (2022) 000–000

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according to (1). The use of more than one bolt is not fully appreciated by racks designers and producers, which prefer the more versatility and adaptability of a single-bolted diagonals to schemes with different geometries. Hence, given that it is hard to increase the resistance of connection without increasing also the resistance of the element, in this paper a new strategy is proposed for the fulfillment of (1), which consists in decreasing diagonal resistance through local reductions of the cross-section. Studies around the design of these reduced parts are carried out and briefly showed in the following, and then experimental validation of the behaviour is performed.

Fig. 1. Configuration of the case study structure.

2. Numerical optimization for the layout of the reduced section The studies around the layout of the reduced sections involve three consequent steps: (i) evaluation of the amount of the reduction of section; (ii) evaluation of the length of the reduced sections (to guarantee the desired level of ductility); (iii) definition of the shape of the reduced sections (to obtain a good performance under cyclic action, considering that this is affected by behaviour in compression). Starting with considerations on the related issues (Moen and Schafer, 2009), reductions are placed at the end sections of the diagonals, immediately before connection spots, to limit the effects on the slenderness of the profile. Steps (i) and (ii) depend respectively on the seismic demand in terms of design tensile force on the bracings and of relative displacement demand of the inter-story levels. In particular, the reduced section shall have a sufficient plastic tensile resistance , to verify eq. (3), and local ductility demand (for each brace and for each level) shall be evaluated starting from global ductility demand of the structure. · ℎ � ≥ , ≥ (3) Assuming that around 50% of reduction of cross-section may be necessary to verify eq. (3), different hole configurations for a C section (which is typical for diagonals of ARSWs’ racks) are analyzed through numerical simulations with ABACUS® software to assess the best shape and length of each reduced section together with the distribution of reduced sections along the element, with the final aim of having a good performance under compression load (slenderness of the brace is one of the parameters to control according capacity design rules for X tensile only diagonals according to Eurocode 8 ( EN 1998-1:2004: Eurocode 8: Design of structures for earthquake resistance – Part 1: General rules, seismic actions and rules for buildings. , 2004, p. 8). Indeed, a global buckling mode under compression force is aimed, considering that local buckling of the reduced parts may induce strong localized damage, that could negatively affect the behaviour of the diagonal under cyclic load. Performance under axial compression load is numerically evaluated and compared for the intact diagonal (no reduced sections are introduced) and for the different configurations of the reduced sections. Fig. 2a shows the load-