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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While the first two parameters, peak ground acceleration and topographical category, can be determined in all cases through the data relating to the location of the bridge collected in the Level 0 census and from the Level 1 visual inspections, the determination of the subsoil category requires specific information on the stratigraphy of the subsoil, which can be obtained from the available design documents or from specific surveys (Borzi et al.,2015, Clarke et al.,2016), in order to consider the amplification of the seismic acceleration according to the construction site, the classification of the seismic hazard must be corrected. In the event that such information is not available, it is necessary to proceed as a precaution assuming the worst of the categories of subsoil reasonably foreseeable for that site. The combination of these parameters allows to determine the seismic hazard class associated with the bridges, according to the logical path. 3.2. Calculation of the seismic vulnerability The seismic vulnerability of bridges depends on the structural characteristics influencing their seismic behavior, and on how they respond to the demands induced by seismic actions. It is evident that bridges characterized by different static patterns, spans and materials have different behaviors towards seismic actions. This essentially depends on the redundancy of the static schemes and their dynamic behavior, the number of vulnerable elements subject to seismic action, such as piers and support devices, the mass of the structures, the level of conservation of the artifacts at the time of the seismic event and the presence of any other elements that contribute to increasing the vulnerability of the bridge to seismic actions; this is the case, for example, with skewed decks. To take into account these differences in behavior, the first classification that needs to be done depends on the static scheme, span length and material. Another variable that influences the seismic behavior of the structures is the way in which they were designed and, in particular, the use of specific seismic design criteria. In fact, it is necessary to consider the eventuality for which the seismic action was not taken into account at all in the design of the structures. These aspects are strictly correlated with the technical reference standard for the design of the bridge. Historically, in fact, with the exception of specific decrees issued following strong earthquakes that occurred on the Italian territory, on the basis of which areas characterized by high seismicity were identified (for example Royal Decree No. 193 of 18/4/1909 following the Messina earthquake), it is necessary to wait for the Italian Law n. 64 of 2/2/1974 to have a more careful approach to the problem of seismic safety and even Ordinance no. 3274 of 20/3/2003 for the seismic classification on a probabilistic basis of the entire Italian territory and for the first technical standards of seismic design in a single document including the different types of constructions and materials. Based on the design regulations, the design year and the construction site, therefore, it is necessary to distinguish bridges built according to seismic design criteria and bridges built with criteria in which seismic action was not taken into account in the design.

2 Determination of Seismic Vulnerability

Bridge material

Single or multiple spans

Reinforced Concrete

Bridge material

Single or multiple spans

Reinforced Concrete Prestressed concrete

Single

Single Isostatic High

Structural scheme

Multiple

Bridge lenght

Masonry Steel

Material, Spans, Scheme, Lenght M-H

Structural scheme

Bridge lenght

Isostatic Iperstatic

High

Medium-Low

Design criteria Seismical Non Seismical

Design criteria

Seismical

Design criteria

M-H

Defect level High Medium-High Medium-High Medium-Low Low

Defect level

Medium-High

Seismical Vulnerability AC M-L

Fig. 4. Determination of the seismic vulnerability.