Ambient vibration testing and condition assessment of the Paderno iron arch bridge (1889)

The Paderno iron arch bridge, erected in 1889 and still used as a combined road and rail bridge, is the most important monument of XIX century iron architecture in Italy. The bridge, with an arch span of 150 m, has a total length of 266 m between the abutments and about 2600 tons of wrought iron were used in its construction.After a description of the historic structure, the paper presents the results of the experimental modal analysis of the bridge. The dynamic tests, performed in operational conditions (i.e. under traffic and wind-induced excitation) between June and October 2009, represented the first experimental survey carried out on the global characteristics of the bridge since the load reception tests (1889 and 1892) and suggested the opportunity of installing a permanent dynamic monitoring system on the bridge with Structural Health Monitoring purposes.

► Different state of preservation of the iron members on the downstream and upstream sides of the historic bridge.
► Slight variation of the natural frequencies of the vertical bending modes in operational conditions.
► Non-reversible decrease of the natural frequency of the first bending mode after the first test.
► Operational modal testing and analysis are effective tools for the SHM of the bridge.