PSI - Issue 64

Filippo Andreose et al. / Procedia Structural Integrity 64 (2024) 40–47

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3.2. Molo VII bridge

Molo VII bridge is a concrete box bridge about 2 km long located in the Italian region of Friuli-Venezia Giulia, along the SS202 State Road (Fig. 4a). The deck is composed by 36 spans of 55 m length each, and 18.50 m wide, grouped in 11 longitudinal sections, each characterized by a continuous girder scheme supported by 3 reinforced concrete piers, with two cantilevers of length equal to half of the deck span. The deck is made with a pre-stressed reinforced concrete section, consisting of a closed trapezoidal geometry. In 2015, due to excessive vertical displacement of some cantilevers, the bridge was reinforced with a cable-stayed steel system anchored to the existing structure (Fig. 4b).

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Fig. 4. Molo VII Bridge: intradox view (a) and detail of the system of the cable-stayed steel retrofit system (b).

A dynamic monitoring system was installed in the bridge with the aim of testing it with P3P. The system is only installed on 5 sections of the bridge, for a total of 134 MEMS-based accelerometers covering 215 measurement channels (Fig. 5). Wind and traffic were the main sources of excitation for the structure.

Fig. 5. Detail of sensors distribution for the decks sustained by the cable-stayed steel system.

OMA modal analysis was performed using P3P software, starting from data collected by the monitoring system. For better results, the single sections were analyzed separately. Ambient vibrations from channels of vertical sensors have been processed including a linear, and down-sampling to 50 Hz. SSI-cov was performed between frequencies of 0.1 Hz and 12.5. Fig. 6 shows stabilization diagram and MAC diagram obtained from SSI-cov analysis on the first section of the bridge. Frequency tracking was performed with P3P over a period of approximately 3 months, from 10 January to 31 March 2023. The frequencies related to the main vibration modes were manually identified: Fig. 7a shows as sake of example the frequency tracking carried out with P3P software for the first section of Molo VII Bridge. Some multiple linear regression statistical models have been implemented, using the temperature data measured by some environmental sensors. An operational test of the P3P software was performed by partitioning the data in