PSI - Issue 64

Massimiliano Ferraioli et al. / Procedia Structural Integrity 64 (2024) 1017–1024 Ferraioli et al./ Structural Integrity Procedia 00 (2019) 000–000

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concrete, featuring frames primarily oriented longitudinally, with transverse frames only at the edges. The locker room building spans five levels and has a rectangular plan, with an additional appendix extending to the basement floor level. This appendix is equipped with underground concrete walls around its perimeter, while another concrete wall on the opposite side reaches a height of 2.44m. These walls, combined with the limited presence of frames, contribute to the building's response being influenced by torsional phenomena (Fig.2, Table 1a). The floors are of a later cementitious type with a thickness of 24cm, including a 4cm slab. The soil was categorized as ground type B. The geometric survey was accompanied by extensive investigations and tests to reach a knowledge level (KL2) according to the Italian Code (2018). Consequently, the average material strength values ( f cm =38.4 MPa for concrete and f ym =463.5 MPa for steel) are divided for a confidence factor of 1.2 to obtain the design values. The seismic assessment was carried out by pushover analysis. The RC structural elements were simulated using SAP2000 computer program (2023), employing fiber plastic hinges at their ends. The cross-section was divided into fibers of three materials: steel for reinforcing bars, confined concrete within the inner layer of hoops, and unconfined concrete outside the hoops. A bilinear hysteretic model was applied to the reinforcing steel bars, while the Mander model (1988) was utilized for confined concrete. The pushover analysis was conducted utilizing two distinct groups of force distributions: 1) load pattern obtained from a modal combination of story shear, 2) "uniform" load pattern. Additionally, an accidental eccentricity ( e ) of 5% was considered. As an example, Fig. 3 shows the collapse mechanism (Fig.3a), the pushover curve (Combination +F x -e y , Group 1), and the comparison between demand and capacity in ADRS (Acceleration Displacement Response Spectra) format. The Limit States of Immediate Occupancy (IO), Damage Limitation (DL), Life Safety (LS), and Collapse Prevention (CP) were checked. Ductile and brittle member capacities were assessed in terms of chord rotation and shear strength, respectively. The seismic safety verification synthesis is presented in Table 2, which includes the following results: capacity of the existing building concerning peak ground acceleration (PGA) and return period ( T r ) for various limit states, along with the corresponding safety index ( ζ = capacity/demand ratio).

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Fig. 1. (a) External view; (b) Base floor plan view of the school building.

a) c) Fig. 2. a) First flexural X-torsional mode shape; b) First flexural Y-torsional mode shape; b) Second flexural Y-torsional mode shape. b)