PSI - Issue 44

Manuel Capogna et al. / Procedia Structural Integrity 44 (2023) 705–712 Manuel Capogna et al./ Structural Integrity Procedia 00 (2022) 000–000

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2. The seismic attention class The definition of the seismic attention class takes into account the main parameters that influence the response to the seismic actions of the bridges and road networks to which they belong. Similarly to the definition of the structural and foundational attention class, the seismic attention class depends on factors of hazard, vulnerability and exposure, determined through the combination of primary and secondary parameters. The approach used for the determination of the Seismic Attention Class (SAC) is, once again, an approach for logical classes and operators, for which logical flows must be followed that allow to pass from the classification of the primary and secondary parameters, to the classification of the hazard factors, vulnerability and exposure and, finally, to the determination of the SAC. As can be seen from the structural and foundational attention class, some of the parameters considered are the same. However, unlike the exposure parameters, i.e. Average daily traffic (ADT) and mean span length, road alternatives, type of bypassed entity and transport of dangerous goods, the definition of which can be taken as such to that used for the structural and foundational, the vulnerability parameters, such as static scheme max span, material and level of degradation, even if indicated with the same wording, are taken into account with partially or totally different criteria.

Table 1. Italian Bridge Guidelines parameter for the classification (MIMS,2020). Seismic Risk Component Primary Parameters

Secondary Parameters

Hazard

Expected peak ground acceleration (return period Tr = 475 y) Level of degradation, static scheme max span, material Average daily traffic and mean span lenght

Soil class

Vulnerability

Design according to seismic criteria Road alternatives, Type of bypassed entity, transport of dangerous goods, strategic funcion

Exposure

The evaluation of level of degradation, which can be realized starting from the information collected during the visual inspections is of prime importance and allows to identify the main characteristics and state of preservation of these structures (Buratti et al. 2022a). Many of the bridges built between the '50s and '60s show structural and technological deficiencies essentially linked to the construction period. They are “afflicted by design” due both to the lack of anti-seismic structural codes and to shortcomings related to the technologies and materials of the time. Moreover, a lot of these structures have been realized through in prestressed reinforced concrete, that as it is known they do not have a plastic reserve, so before the collapse, more often there are no evidence of structural failure (Bazzucchi et al, 2018). In addition to the vulnerability of the static scheme, usually consisting of continuous supported beams, must be added the increase in road traffic loads. In fact, starting from the first code of ’33 up to the current Technical Standard for Constructions (NTC2018), several different approaches and load schemes have been assumed by the codes. (Bencivenga et al., 2022). In the evaluation of SAC the main difference is related to hazard, depending on the expected peak ground acceleration (Pga) that is taken from the Italian seismic hazard map based on the bridge’s geographic coordinates that is combined with the topographic condition. The ground type to be considered for each single bridge structure is not directly available. As for vulnerability, the primary parameters are evaluated with respect to structural components having an influence on the seismic behaviour, while a secondary parameter is represented by the earthquake resistant design level. In particular, the bridges designed considering seismic actions have to be distinguished from the more vulnerable bridges designed only relative to gravity loads. To this scope, the construction period will be helpful in identifying the adopted structural design code and related criteria. Finally, the possible strategic function for civil protection purposes must be considered (Buratti et al., 2022b, De Matteis et al.,2022).