Elastoplastic structural analysis of the Paderno d’Adda bridge (Italy, 1889) based on limit analysis

The Paderno d’Adda bridge is a beautiful iron viaduct built in 1889 by the Società Nazionale delle Officine di Savigliano (SNOS), in response to needs from rapidly-growing industrial activities in Lombardia towards the end of 1800. Specifically, within the expansion of the local railway network, it became necessary to acquire an elevated crossing on the river Adda, North-East from Milano. The remarkable structural concept elaborated for the bridge by designer Jules Röthlisberger (1851-1911), head of the SNOS Technical Office since 1885, was that of raising a stiff but slender symmetric doubly built-in parabolic arch among the two banks of Paderno d’Adda (right bank) and Calusco d’Adda (left bank), of about 150m of horizontal span and 37.5m of vertical rise, supporting then, together with vertical truncated pyramidal piers, a straight upper box continuous beam on nine bearings of 266m of length. The present research study has been developed in the direction of modelling the global non-linear elastoplastic behaviour of the bridge. Reference is still made so far to the characteristics at design stage; the hypothesis of perfect elastoplastic behaviour with unlimited ductility of all the structural members has been assumed. In particular, focus is made here on the determination of the collapse load multiplier and relevant collapse mechanism, for various static try-out railway loading conditions on the bridge.