Built in 1887 on Julius Röthlisberger's design by the Società Nazionale delle Officine di Savigliano, the bridge is thus over 130 years old and is used by both road and rail traffic (SP 54 and SP 166 roads), thanks to its two levels.
It is considered a masterpiece of Italian industrial archaeology, and links the cities of Paderno d’Adda and Calusco d’Adda. It is 267 metres long, and has a span of 37.5 metres and rises to 85 metres over the River Adda. It was built using 5,000 cubic metres of stone from Moltrasio, 1,200 cubic metres of Baveno granite, 2,515 tonnes of cast iron and 100,000 nails.
The roadway is five metres wide, and has a single lane, with footways on either side. The lower level of the bridge carries the Seregno-Bergamo and Milano-Carnate-Bergamo rail lines, and the higher one carries the road that links the provinces of Lecco and Bergamo.
Urgent extraordinary maintenance work that could not be delayed made it necessary to close the bridge on 14 September 2018. When closed, the bridge showed generalised corrosion and deformation of the iron elements, accumulation of sediment, deteriorated joints and, on the higher level, unusable walkways, roadways that were at the end of their lives and an obsolete guard rail.
In 2017 3D geometric surveying was carried out for use in the structural modelling of the entire work, which meant that stress could be periodically monitored. The most recent update on structural checks, which was presented to RFI on 14 September last year, showed how the safety coefficients relating to a number of bridge components were beyond acceptable parameters.
The two-year work plan set out by Rete Ferroviaria Italiana (FS Italiane Group) involves both the road surface and the railway itself.
In the first case, one of the many things scheduled is the demolition of the existing road surface, and the complete substitution of the expansion joints. As far as the railway bridge is concerned, the work mainly consists in replacing all the metal components.
The plan was presented in the meeting held on 9 October 2018 – which was attended by the Minister Danilo Toninelli, and parliamentarians from the provinces of Bergamo and Lecco, the Region of Lombardy, the presidents of the provinces and the mayors of the municipalities involved.
During the meeting, the FS executives gave a detailed explanation of the work undertaken to deal with the emergency and the timeframe for work to start.
The bridge rebuilding work has been entrusted to the Temporary Association of Companies (RTI) formed by Luigi Notari Spa (lead constructor), FADEP (principal constructor) and by the RTI of Seteco Ingegneria srl (lead planner) and the engineer Pier Giorgio Malerba (principal planner).
The work is expected to cost around 21.6 million euros, of which 1.6 million will be provided by the Region of Lombardy.
To speed up the execution of the extraordinary maintenance work on the San Michele Bridge, the government has appointed Maurizio Gentile, the CEO and General Manager of RFI, pro tempore Commissioner.
The Commissioner's institutional role means that he is responsible for speeding up the authorisation process relating to the planning stages, by issuing ad hoc orders.
The aim is to reduce the time needed for the work, so this important piece of connection infrastructure is once again available to the regions affected as soon as possible.
During the check conducted on 14 January 2019, the Commissioner confirmed that cycle and foot traffic will be able to start again during March, and also announced that road traffic may start by the end of 2019, with alternating, one-way vehicular traffic, but with the ban on heavy goods vehicles maintained.
The work is expected to be finished by the end of 2020.