A structure such as the Polcevera viaduct in Genoa should never, ever collapse.
Anywhere in the world. It certainly should never happen in a western European country such as Italy.
Investigations into the cause of the collapse will be thorough and will be pored over by bridge engineers worldwide. Already a number of theories are circulating – but until the investigation is completed, it is only possible to speculate.
What should be said is that the Polcevera viaduct was amazing in its time, and its designer, Riccardo Morandi, was a genuine innovator.
New Civil Engineer’s founding editor, Sydney Lenssen, visited the Genoa viaduct in 1965 and insists it was a miracle in its day. And he recalls that despite reservations about the “unusual design”, Morandi’s ambition was infectious and he was heralded as a genius at the time.
Morandi was determined to explore the concept that evolved into cable-stayed technology and was equally determined to push the use of prestressed concrete.
Clearly it would never be built in the same way today. Cable stay technology has massively advanced. But that does not mean Morandi designed a bad bridge.
It is now emerging that Morandi’s bridge has required considerable maintenance over the years – we have pictures that clearly show strapping around many critical beams, and have confirmed that plans were in place to strap the section that failed.
There is no shame in that: many bridges of that era are in the same situation, principally because no bridge designers of that era foresaw the long-term durability issues and excessive traffic loads that would affect their structures. No one did.
In the aftermath of Polcevera, Highways England has reassured road users that its bridges of that age are under control. But that is only because here in the UK we have had our warnings and acted on them: severe cable corrosion first detected in the Humber Bridge warned that the Severn and Forth Road bridges may need intensive remedial works and constant, 24/7, monitoring. In all three cases dehumification of tendons and acoustic monitoring keep the structures serviceable.
In the UK, every structure, from culverts under roads to multi-span viaducts, must be visually inspected every two years. Every six years they must be investigated by people within hand touching distance of the components, with reports made on their condition, followed up by programmed and budgeted corrective maintenance works.
The owner and operator of Morandi’s bridge, Autostrade, has insisted it was aware of this need, and that it, too, had its bridge under routine maintenance and constant surveillance. Clearly a large part of the investigation needs to focus on just what that maintenance and surveillance was, and how it was deemed sufficient.
But back here in the UK there is no room for complacency. Despite the warnings about corrosion from the Humber, Severn and other bridges, and despite the lauded inspection regime, the Hammersmith Flyover nearly became the UK’s own international incident of when major defects were detected just before the start of the 2012 Olympics – prompting immediate closure and urgent remedial works.
Some clever, award-winning engineering has now restored that structure to full use, but it was a very near-thing at the time.
So that has to be the lesson. There are thousands of 1960s and 1970s bridges worldwide, many of them as unique as Morandi’s in their design, and all of them in various states of (dis)repair. Keeping them going is clearly going to become an ever more invaluable skill.
- Mark Hansford is New Civil Engineer’s editor