PSI - Issue 44

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

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the seismic risk of the existing reinforced concrete buildings. The main techniques of seismic reinforcement can be summarized as a localized approach (Comodini et al. 2021), which consists of the structure's consolidation using a localized reinforcement of the frame's joints, beams, and columns, and in a global approach, whereby the building is reinforced by inserting new, seismic-resistant elements. The choice of intervention technique is reduced by the added requirement that, during the intervention, the structure's operation and/or use must not be interrupted (FEMA, 2006). This requirement is generally a must for strategic buildings, public utilities, or sites of production activities, and in all cases where interruptions to their operation can lead to heavy burdens and social repercussions. Interventions whose global approach allows structures to continue their operation include all types of interventions that take place outside the building itself, using additional structures, which are connected laterally to those already in existence and which sit on independent foundations. These systems are called "exoskeletons"; namely, they are systems that are attached to the outside and which can protect the existing construction, mainly by increasing its capacity for lateral actions (Di Lorenzo et al., 2020). The exoskeleton can be conceived with solutions that offer a range of alternatives (Foraboschi and Giani, 2018).: the adoption of braces integrated within the exoskeleton (solution for walls or dissipative towers) or, in an innovative way, by using an enveloping design that acts like a seismic-resistant, box-like system (shell solution) (Feroldi et al. 2014) The choice of structural solution depends on the building stiffness and can be conceived about the resistant capacity or the dissipative capacity ( Reggio et al. 2018). Wall solutions encompass, for example, the use of bracing frames with rigid or dissipative connectors, dissipative bracings, hinged walls at the base, rocking walls, or adaptive seismic walls. However, one of the most delicate aspects of the application of this technique concerns how the exoskeleton is coupled to the existing structure. The type of coupling depends on the type of exoskeleton and can be of the local type on the frame joints, or the diffuse type on the beams of the floor slab. The coupling devices must ensure that seismic actions are transferred from the existing structure to the exoskeleton without generating abnormal stresses that the original structure would not be able to withstand without reinforcement. This article presents the use of a coupling device that is capable of transferring the shear plane forces and which thereby allows for vertical sliding movements between the two structures positioned side by side. The features of the device ensure that the flexural deformations of the exoskeleton do not interfere with the deformations of the existing structure and reduce the formation of critical axial stresses in the column.To evaluate the effectiveness of the coupling system under study, it was used in a seismic improvement intervention of a real building for which the use of exoskeletons consisting of shear walls with a steel reticular structure is envisaged.

2. Seismic vulnerability analysis of the case study building 2.1. Building description

The building being studied was built in the 1950s and is located in Perugia, Italy. It is used for educational and laboratory purposes. The building includes five story in elevation, a partially underground story, and an attic story. The building's height above ground is 26.50 meters, with the height of the interstory varying from 3.00 meters to 3.80 meters.

Fig. 1. Longitudinal prospect