On 14th August 2018 the Morandi Bridge (Ponte Morandi) in Genoa collapsed with initial fears that more than 30 people lost their lives. As you might expect, the Genoa Bridge collapse has created concern and confusion in the engineering sector and politicians have already started the blame game. This will go down as one of the worst bridge collapses in modern times. However, if we strip away the emotion and look at the cold hard facts, why did the Genoa Bridge collapse?
History of the Morandi Bridge, Genoa
We know that the bridge was designed by Italian civil engineer Riccardo Morandi with construction starting in 1963 and ending on 4 September 1967, when the bridge was opened. The bridge is part of the A10 motorway in Italy and crosses the river Polcevera in the district of Genoa. There are three reinforced concrete supporting piers climbing 90 metres into the sky and the bridge spans a total of 1102 m. At the time the design of the bridge was hailed as revolutionary. Using A-frame towers to hold the reinforced concrete stay cables in place, with V-shaped supports below the deck, to stiffen the bridge and reduce degradation, it was hailed as a major step forward.
While investigators begin to gather evidence to try and find out what caused this catastrophe, there is talk about a similar bridge designed by Riccardo Morandi in Venezuela back in 1957 (General Rafael Urdaneta Bridge).
Unfortunately, the General Rafael Urdaneta Bridge situated by Lake Maracaibo in western Venezuela also experienced a partial collapse back in 1964. This particular incident was caused when a tanker crashed into one of the spans. While there are no initial reports of a similar collision on the Morandi Bridge investigations are at a very early stage.
Continuous maintenance of Genoa Bridge alarmed experts
While hindsight is a very useful tool, if we look back to the early days of the bridge we see a structure which received significant restoration work in the 1970s. Many structural engineers highlighted the alleged miscalculation of the effects of viscosity on the prestressed concrete which was vital to the structure. There is a growing opinion that this miscalculation led to excessive deferred displacement of the road deck which prior to further work in the 1980s was described as “neither level nor horizontal” at its worst points.
In the 1990s, traditional external steel cable supports were added to the east side pillar which many people believed would significantly extend the life of the bridge. In what could prove to be a telling indictment of the state of the bridge we know that on 3 May 2018 a €20 million tender was announced for a structural upgrade of the bridge. The deadline for the tender offer closed on 11 June 2018 and when the bridge collapsed it has been widely reported maintenance work was ongoing to improve the foundations of the structure.
What may have caused the Genoa Bridge collapse?
Slowly but surely more information is leaking into the public domain regarding the state of the structure, the potential issues identified and the extreme weather conditions on the day of the Genoa Bridge collapse. There are a number of trains of thought as to why the bridge collapsed:
Extreme weather conditions
The Genoa Bridge collapse occurred during extreme weather conditions which saw torrential rain and lightning strikes. Witnesses suggest that the bridge may have been struck by lightning just prior to the collapse with concerns that this could have compromised the reinforced concrete stays. This would have created extreme pressure on the remaining stays leading to an inevitable partial collapse. However, many experts are suggesting that a lightning strike on its own should not bring down a structure of this nature but, as we know, there was already ongoing degradation and the structure may well have been compromised prior to any strike.
Fatal flaw in the original design
As we touched on above, the fact a similar bridge designed by the same engineer collapsed in Venezuela in the 1960s is fuelling concerns about the initial design. The use of prestressed concrete to encase the supporting stays was revolutionary at the time but is not a method used today. It may well be something as simple as the miscalculation of the impact viscosity would have on the prestressed concrete which led to the collapse. Reports of uneven road surfaces on the bridge were allegedly addressed during the 1980s but constant reports of above-average degradation have haunted the structure for decades.
Issues with maintenance
Such was the growing cost of maintaining the Morandi Bridge that many experts had publicly recommended building a new bridge to the North and dismantling the original bridge. We know there was significant structural work in the 1970s, 1980s and 1990s with constant tweaking and repairs prior to the 2018 tender offer. We also know that maintenance work was ongoing as the collapse occurred but constant monitoring of the bridge appears to have shown no cause for alarm prior to the unexpected failure.
Figures from the OECD also cast a very interesting light on investment in road networks by the Italian authorities. Just prior to the US sub-prime mortgage collapse in 2007, which led to a worldwide economic crisis, the Italian government was spending in the region of €14 billion per annum on roads. This figure fell to €6 billion in 2009, falling to below €3 billion in 2013 and while it has since recovered to around €5 billion in 2015, this does not compare well to European counterparts. Does the fact that 12 bridges/overpasses have collapsed in Italy since 2004 add further strength to concerns about the road maintenance budget?
The Italian government has confirmed that the Morandi Bridge was used by 25 million vehicles each year. Despite plans to erect additional bridges to reduce annual traffic flow across the Morandi Bridge, traffic was still expected to increase by 30% up to 2020. The 14 August 2018 heralded the start of a public holiday in Italy with many people using the bridge to get to their traditional French vacation. A 2011 report by the Italian highways company Autostrade per I’Italia confirmed that the excessive daily traffic and rush-hour queues were placing major demands on the structure of the bridge. The official report also confirmed the impact of ongoing degradation.
As investigations continue into the reasons for the Genoa Bridge collapse the likelihood is that initial structural issues, reduced maintenance spending, extreme weather conditions and traffic use far beyond expectations will all have played a part. There will be renewed inspection of bridges both in Italy and further afield, road spending will probably increase in the short term and legal action will likely follow in the event of negligence by one of more parties.
While the specific design of the Morandi Bridge was hailed as revolutionary in the day, structural engineering has moved on and there are very few comparable structures today. Once the rescue process comes to a close it should be fairly easy for structural engineers to find evidence to determine the reasons for the collapse. We can only hope that lessons are learnt and, as far as possible, disasters like this can be averted in the future.