PSI - Issue 44

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Fabrizio Comodini et al. / Procedia Structural Integrity 44 (2023) 1076–1083 Author name / Structural Integrity Procedia 00 (2022) 000–000

1078

The building plan has an elongated rectangular shape and is geometrically irregular due to a reduction in width in one of the extremal areas. The structure consists of multi-story, reinforced concrete frames which are positioned in a transverse direction and regular in height. There are 26 frames, with a 3.00 m center distance. The frames of the first 18 alignments have two spans. The remaining 8 frames are single-span in structure and concern the portion of the building with a reduced width. In the first and second levels, there are also concrete walls that mainly perform the function of containing the thrust of the ground on the upstream side. The building's plan is laid out as a rectangle with the following dimensions: 75 meters in the longitudinal direction and 15 meters in the transverse direction. The floors consist of concrete slabs with a total thickness of about 210 mm including the upper reinforced concrete slab. The foundations consist of plinths on piles.

Fig. 2. Building plan

2.2. Properties of the existing materials To define the mechanical characteristics of the materials and the quantities of steel for reinforced concrete, a campaign of in situ diagnostic investigations was carried out. The results of the investigations made it possible to reach an LC2 level of knowledge as specified in the NTC 2018 and therefore a confidence factor FC = 1.20. The values of the mechanical characteristics of the existing materials are reinforced concrete steel f ym 354.40 Mpa and concrete f cm 12.20 Mpa. 2.3. Seismic hazard and design spectrum The subsoil's mechanical characteristics were defined through on-site and laboratory surveys. The foundation ground can be classified as subsoil category B. The Peak Ground Acceleration (PGA) was defined as starting from the "basic seismic hazard" associated with the building's reference life, VR = 75, and amplified using the soil factor Ss = 1,179 and the topographical factor S T = 1.0 The PGA values (ag/g) for the return periods of the seismic action corresponding to each limit state are shown in the following table.

Table 1 Seismic hazard Limit states

Seismic Demand

ag/g

Return Time

Limit state of operation Damage limit state Safeguard limit state Collapse limit state

0,077 0,097 0,227 0,281

45 75

712

1462

The forms of seismic response spectra used for safety assessments are those indicated by the technical code (NTC18).