PSI - Issue 44

Gianfranco De Matteis et al. / Procedia Structural Integrity 44 (2023) 681–688 Gianfranco De Matteis et al. / Structural Integrity Procedia 00 (2022) 000–000

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highlighting the operability or adequacy of the bridge as a whole, rather than of individual elements. Anyway, the use of local rather than whole models is in charge to the expert judgment of the engineer, who may profitably use outcomes of linear applications for selecting the best analysis approach. 3. Case study 3.1. Description of the bridge The case study examined in this paper is a two-span reinforced concrete bridge. The bridge is constituted by two 12.30 m wide and 10.80 m long simply supported decks, each one composed by six 30 cm wide and 1.10 m high beams transversally connected through 3 cross-beams located at each deck supports and in the middle span, and by a 20 cm thick reinforced concrete slab. The cross-beams at supports have a cross-section of 30×115 cm, while the middle span cross-beam has a cross-section of 20×100 cm. The study at hand is devoted to the linear and nonlinear analysis of the deck, with focus on the safety assessment of the deck slab; thus, only one of the two simply supported decks is analysed; for the same reason, substructures (i.e. abutments and pier) are not included in the applications in view of the bridge static scheme. The latter are constituted by 2 wall abutments and a frame pier with an overall high of about 5 m. Fig. 2 shows a longitudinal view of the overall bridge, together with a plan view and a cross-section of the deck, and the slab transverse reinforcements. In addition to the structural self-weight, gravity loads are due to a 40 cm thick pavement, characterised by a density of 20 kN/m 3 , and by steel traffic barriers having a weight of 1.5 kN/m. Finally, traffic loads defined by the Italian NTC2018 (MIT, 2018) are considered in the applications, and loads are combined consistently with the Ultimate Limit State foreseen by Italian standard. 3.2. Linear analyses Linear applications of the case study at hand were performed, according to considerations provided in the previous section, to evaluate the load schemes producing the maximum and minimum bending moments on the concrete slabs, to address the decks load redistribution capabilities and to provide a benchmark to control the results of nonlinear applications. Furthermore, in order to evaluate the reliability of different linear modelling approaches, different strategies were adopted, moving from a simplified 1D beam model (typically used by practitioners) of a slab strip, to more refined 3D global models of the deck, implementing beam or solid elements. For all the models, loads were those provided by the Italian code NTC2018 for bridges; in detail, both load schemes 1 and 2 were considered to study the longitudinal and transversal distribution of loads providing the maximum and minimum bending moments on the slab. Concentrated loads of both schemes are assumed to be distributed over the relevant loaded areas, as indicated in the code, suitably increased considering a further diffusion of the load within the pavement thickness and the half thickness of the slab, according to an angle of 45°. Preliminary considerations based on the expert judgment were performed to reduce the number of load configurations to be considered in the linear applications, and two final loading conditions, producing the maximum (LC1) and minimum (LC2) bending moments were finally defined.

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Fig. 2. (a) Longitudinal profile of the bridge; (b) plan view of the deck; (c) cross-section of the deck and (d) transverse slab reinforcement.