Riccardo Morandi (1902-1989) was an Italian civil engineer and bridge designer who was one of the earliest proponents of designs that used mainly prestressed concrete, rather than mostly steel.
In 1967, a bridge he designed was put into service in Genoa, Italy. It spanned a river, some railroad tracks, and other portions of the city with three tall pylons, each of which had concrete stays reaching diagonally down to the roadway, which was suspended some 145 feet (44 m) above the ground. It came to be known as the Morandi Bridge, after its designer.
On Tuesday, August 14, during an intense rainstorm one of the tower-supported sections of the bridge suddenly collapsed. As of today (August 26), a total of 43 people have died as a result of the accident, not to mention injuries and property damage, which will total in the millions. Government officials have called for the revocation of the contract with Autostrade per l’Italia, the private firm that handles highway maintenance in Italy. One mourner at the state funeral held for many of the victims said that “In Italy, we prefer ribbon-cuttings to maintenance.”
Engineering experts consulted by the media all said it was too soon to draw any conclusions about what might have caused the bridge to fall. Bridges designed by Morandi have a history of requiring more maintenance than more common designs do. The stark elegance that may have appealed to clients around the world who were looking for something distinctive to add to a city skyline was achieved at a cost of asking a lot of the material that was used in the bridges Morandi designed.
As we have mentioned before, pure concrete has almost no strength in tension, so to use it as a structural material, it has to be reinforced with steel “rebars” and other components that can withstand pulling stresses. This would be especially true of the stays that slanted down from the tops of the towers to support the roadbed. Over time, corrosion can attack these tension members, sometimes invisibly deep within a vital member of the structure.
The evidence of why the bridge collapsed is buried in the huge piles of rubble that workers will need to clear meticulously and carefully. Because such work is both a huge project on its own and demanding of attention to detail, it may be months or even years before we have an answer to the question of why the bridge collapsed. After a bridge in Minneapolis collapsed in August of 2007, it took over a year for the US National Transportation Safety Board to issue its final report on the accident, which attributed the collapse to a design flaw that made a gusset plate too weak.
The problem with forensic investigation of prestressed-concrete bridges is that concrete is a much more complex material than steel. Unlike steel, which is fabricated under carefully controlled conditions in a steel mill, concrete is often formed onsite, and the way it is mixed, poured, and treated after pouring can influence its ultimate strength and other properties.
Nevertheless, most prestressed-concrete bridges withstand the stresses they were designed for, and so the reasons for the Morandi collapse will be interesting to discover, if they can be found.
While we still do not know whether the collapse was due to an initial design flaw or faulty maintenance, the question of maintenance for bridges and other vital pieces of infrastructure is an urgent one that industrialized nations all around the world are struggling with. In 2017, the American Society of Civil Engineers (ASCE) gave the US a D+ in its “infrastructure report card,” saying that 56,000 bridges (about 9% of the total) were “structurally deficient” in 2016. While the situation has not reached such a crisis that we see bridges falling down every month, tragedies like the Morandi collapse remind us that the price of deferred maintenance is sometimes much higher than anyone would like to pay.
It’s a little bit like preparing for war. The only way you know you didn’t spend enough money on preparing for a war is if you lose it. You can win with barely enough resources, or with three times more resources than you need, and the result is the same. The art and science of maintenance consists in doing enough to prevent nearly all major tragedies and to do something about minor problems fast enough, while not simply wasting resources on painting a wall that doesn’t need painting, for example.
Judging by the rarity of bridge collapses, most bridges were either built well enough to start with to survive many decades with whatever maintenance they’ve received, or have been maintained well enough to keep standing. But the shock value of a major bridge collapse is one of the main motivators for public funding of infrastructure maintenance, which has none of the appeal of new construction.
Engineers are mostly used to working out of the limelight, doing dull but necessary things like scheduling expensive maintenance that takes money away from flashier and more popular government activities. Riccardo Morandi was somewhat an exception to this rule, attaching his name to striking bridge designs that caught the eye of the public time after time. If there’s the equivalent of an Internet connection wherever he is, I’m sure he’s sorry to see what has happened to his creation in Genoa, whether the failure is due to him personally or due to insufficient maintenance over the five decades the bridge has carried traffic since it opened.
But maintenance is a job for the living, not the dead, and engineers in charge of maintenance owe it to their constituent publics to be sure that tragedies such as the Morandi bridge collapse don’t happen. We look forward to finding out what went wrong in Genoa a couple of weeks ago, and applying those lessons to future problems so that they can be avoided before more people get killed.
Karl D. Stephan is a professor of electrical engineering at Texas State University in San Marcos, Texas. This article has been republished, with permission, from his blog Engineering Ethics, which is a MercatorNet partner site. His ebook Ethical and Otherwise: Engineering In the Headlines is available in Kindle format and also in the iTunes store.