Elastoplastic structural analysis of the Paderno d'Adda bridge (Italy, 1889) based on Limit Analysis

The Paderno d’Adda bridge is a marvellous historical iron arch bridge that was built in 1889. It allows connecting the provinces of Lecco and Bergamo across the Adda river, between Paderno d’Adda and Calusco d’Adda, near Milano, northern Italy. The bridge was designed for railway needs and its use is two-fold: a railway track is located in the inner deck of the upper continuous beam; automotive traffic runs on top of it. Today, after 123 years of continuous duty, the viaduct is still in service, with trains crossing at slow speed and alternated one-way road traffic restricted to no heavy-weight vehicles. Despite these duties, the bridge seems to have suffered from limited maintenance. With the final purpose of elaborating a safety assessment of the structure, an inelastic structural analysis of the viaduct is performed, based on a finite element model that takes into account a perfect elastoplastic behaviour of the various structural members and is apt to comply with typical principles of Limit Analysis. Specifically, the critical load multiplier and relevant collapse mode are investigated, for different static loading conditions on the bridge. Also, the characteristic non-linear load/displacement response curves of the bridge are traced by incremental analyses up to the true limit load and the various critical members of the structure are identified. A further intention of this work consists in promoting interest at the international level on the Paderno d’Adda bridge, as a beautiful, living industrial monument of the scientific and technological developments of that time, by referring particularly to its present and future destinations.