Operational Modal Analysis and Structural Identification of a Concrete Box Girder Bridge

In this paper we report some preliminary results of an experimental/analytical investigation on a prestressed concrete box girder bridge located in Tarvisio (Udine, Italy). The bridge was designed by engineer Silvano Zorzi and built in the 1970s, using the cantilever system developed by the German company “Dyckerhoff und Widmann” with the use of “Dywidag” pretensioned bars. The deck is 12.50 m in width and has two spans of 57.25 m each. The height of the deck varies between 6.00 m at the junction with the central pile and 2.50 m near the bearings. An extensive in situ campaign, aimed at defining the state of preservation of the prestressed reinforcement of the deck was conducted at the end of 2022. The campaign included a visual inspection, a survey of the layout of the prestressed reinforcement using geo-radar, and evaluation of the residual section of the prestressed reinforcement using endoscopic methods. Dynamic test for the determination of the main modal parameters of the bridge were conducted in operational conditions in October 2023. The information obtained from dynamic tests are used for the calibration of a finite element model of the bridge, which will be useful for future diagnostic analyses. The whole research work is preparatory to the rehabilitation and retrofit that the bridge’s owner, ANAS S.p.A., has planned to carry out in 2024.