PSI - Issue 44

Andrea Natale et al. / Procedia Structural Integrity 44 (2023) 1768–1775 Andrea Natale et al./ Structural Integrity Procedia 00 (2022) 000–000

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Peer-review under responsibility of the scientific committee of the XIX ANIDIS Conference, Seismic Engineering in Italy Keywords: Retrofit, Losses, Base Isolation, MATLAB

1. Introduction The lack of proper seismic details in the existing buildings often resulted in high vulnerability against earthquakes as demonstrated by the recent seismic events. Indeed, local brittle failures (often related to the interaction between the structural and non-structural components, see Fig.1) or significant damage to non-structural components may significantly compromise the building performance and post-earthquake repairability. The poor performances of the existing building during recent earthquakes outlined two main directions of improvement: increase the safety at life safety limit state and contain the damage to structural and non-structural components to reduce the economic losses (Del Vecchio et al. 2020). Thus, the modern engineer philosophy should consider these two main objectives for a sustainable design of the retrofit intervention.

a) b) Fig.1. Damage to a) structural and b) non-structural element after a seismic event.

Nowadays different retrofit solutions are available on the market to improve the performance of existing buildings (see Fig. 2 for some examples). They can be grouped in three big categories: traditional, innovative and the low damage techniques. The traditional techniques (e.g. RC jacketing, steel jacketing, etc) aim to increase the strength, stiffness and/or ductility, but they are often characterized by high level of disruption and a medium cost of intervention. Innovative retrofit techniques aim at increasing strength and ductility (e.g. FRP wrapping, see Fig. 2a) with a minimum level of disruption and, in turn, a low cost. Furthermore, low damage solution (e.g. Base isolation, dissipative bracing, see Fig. 2b) aims at reducing the acceleration and drift demand on the superstructure. They are often characterized by high cost of the devices and installation, but with significant benefits in terms of containment of the damage and economic losses. Last, demolition and reconstruction can be also considered as an alternative (expensive and with high environmental impact) to seismic retrofitting (see Fig. 2c)

a) c) Fig.2. Retrofit options for existing RC buildings: a) FRP wrapping, b) Base Isolation, c) Demolition and reconstruction . b)

It is clear that to draw general considerations of the convenience of a retrofit solution respect to another different aspects should be considered. The increasing of safety should be the primary objective. However direct considerations on the cost of installation, benefits in terms of reduction of the EAL should also be considered. To this end an important parameter that can provide insights on the economic convenience of a retrofit technique can be the Pay-Back time, (PBT) defined as the return of the economic investment of a retrofit solution. An accurate assessment of the PBT, as discusses in Natale et al. (2020), needs refined analyses and this could be expensive and time-consuming, thus making