PSI - Issue 44

Marco Gallo et al. / Procedia Structural Integrity 44 (2023) 618–625 Marco Gallo et al. / Structural Integrity Procedia 00 (2022) 000–000

620

3

1 2

2.45 2.67

0.0096 0.0050

3.0 2.7

0.274 0.090

Fig. 2. Mode of shapes.

2.2. Seismic action According to Italian technical references (NTC2018), and more generally to Eurocodes, the loads that must be taken into account in the design of bridges are: the total self-weight of structural and non-structural members ( G 1k and G 2k ), road traffic actions ( Q 1k ), sum of a uniformly distributed load and double-axle concentrated load (tandem system), breaking and acceleration forces, wind load, seismic action. The reference spectra considered for the definition of the seismic action are those related to the city of Naples for the Life-Safety Limit State (as indicated in par. 7.2.2 of NTC 2018). To define the seismic action an importance class IV was considered as the bridge integrity during the earthquake is of vital importance. Based on the information found in the geotechnical report of the original project, the soils at the site of the work under consideration consist of loose material of volcanic origin (pozzolan), overlying a tuff lens of thickness variable from zero to 4 m, located at a depth of about 20-25 m. The MASW test performed on site, on the other hand, showed a soil classifiable, according to NTC2018, as a type C soil, with V s,30 = 333 m/s. According to suggestions in Section 7.3.1 of NTC2018 for reinforced concrete piers mainly subjected to bending moment and in low ductility class (CD "B"), a behaviour factor value q =1.5 was assumed for the analyses. Below, in Figure 3, the response spectra in terms of pseudo-spectral acceleration are shown for the horizontal and vertical components of the seismic motion. Note that only the elastic vertical spectrum is shown in Figure 3, inasmuch NTC2018 prescribes (see section7.3.1) to assume q =1.0 for the vertical seismic motion in case of bridges. In Table 2 the site hazard parameters for the Life-Safety Limit State (SLV according to Italian NTC08) are given.

0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80

SLV_Elastic_horizontale SLV_Horizontal q=1.5 SLV_Vertical

SLV_Orizzontale_Elastico SLV_Orizzontale_q=1.5 SLV_Verticale

S a (T) [g]

Table 2. Hazard parameters.

Limite State

T R [years]

a g [g]

F 0 [-]

T* C [s]

SLV

949

0.212

2.444

0.343

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

T [s]

Fig. 3. Response spectrum

2.3. Dynamic model validation In order to validate the dynamic behavior of the numerical FEM model implemented through SAP 2000, a modal analysis was conducted comparing the values of the vibration periods and numerical modal shapes with those obtained experimentally through the identification test performed on the bridge. Table 3 shows the comparison between the vibration frequencies obtained through dynamic test and numerical simulation, as well as the difference in percentage for the first 5 vibration modes. As can be seen, the model is able to capture with a very good accuracy the real behavior of the viaduct, with differences of 3% for the first 3 vibration periods, 4% for the fourth and 5% for the fifth.