PSI - Issue 64

Donatella de Silva et al. / Procedia Structural Integrity 64 (2024) 1806–1814 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

1808

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characterized based on a representative measure. In this study, presentative measures of fire the peak thermal release (W) and fire load (GJ) were considered. Then the thermo-mechanical analyses are conducted. At the end of the analyses, the maximum and residual vertical displacement of the point located at the center of the bridge span is considered as the response parameter of the structure. This response parameter allows for identifying the maximum demand-to-capacity ratio in function of the specific performance level considered (see Table 1). Once the demand-to-capacity ratio is known for each fire scenario, a logarithmic linear regression of these values is performed, thus providing the necessary value to construct the fragility curves. In particular, a regression is used herein as a probabilistic model to define the conditional probability distribution of dependent variables with respect to independent variable, as it is very widespread in literature by Miano et al. (2023), Miano et al. (2024) and Miano et al. (2024). Then, linear logarithmic regression is herein used to link the structural response to the fire intensity parameters. This is conceptually equivalent to the seismic field in which Cloud Analysis is used as procedure in which a structure is subjected to a set of ground motion records of different first-mode spectral acceleration Sa(T) values by Jalayer at al. (2021) and Jalayer at al. (2021). In this case, once the fire scenarios are applied to the structure, the resulting maximum demand over capacity ratio for performance level (DCRPL) is found. Finally, lognormal fragility curves are obtained, as in the Cloud Analysis for the seismic analysis measuring the capacity of the case study bridges. 3. Case Studies The typological bridges analyzed in this study are two and representative of Italian bridges respectively in prestressed reinforced concrete and steel-concrete composite deck. These bridges were built between the 1970s and 1990s. In most cases, such bridges are characterized by a statically determinate scheme with the deck simply supported, and in most cases the structures exhibit circular pier cross sections. The first bridge analyzed is representative of Italian prestressed reinforced concrete bridges, and the second bridge analyzed is representative of steel bridges. In particular, for the reinforced concrete bridges due to the large variability in geometric and mechanical characteristics of the structure, a single span of the median bridge determinate by Zelaschi et al. (2016), was analyzed. This span was considered simply supported on the piers. The piers of bridge have a circular section. For the second bridge analyzed, a typological composite steel-concrete bridge was used. The geometrical properties of these bridge analyzed are illustrated in Table 2. Table 2. Geometrical properties

Dimensions of concrete bridge

Dimension of steel bridge

Variable

Value

Variable

Value

Pier Haight (m)

7.03

Pier Height (m)

7.05-8.85 ( average 7.95 )

Pier circular section diameter (m)

12.06

Pier circular section diameter (m)

2.00

Span length (m)

31.18

Span length (m)

32.23

Deck thickness (m)

0.2

Deck thickness (m)

0.25 8.50

Deck width (m)

12.06

Deck width (m)

The mechanical properties of the bridge analyzed in this study are illustrated in Table 1.

Table 3. Mechanical properties of the bridges analysed.

Mechanical properties of concrete bridge

Mechanical properties of steel bridge

Bars tensile strength (MPa)

544.4

Steel

Fe510/ S355

Reinforcing bars Young Modulus (GPa)

210

Concrete

Rck > 40 / C32/40