Riccardo Morani (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 Morani 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 (Aug. 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 Morani 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 Morani 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 inthe
huge piles of rubble that workers will need to clear meticulously and
carefully, and 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 U. S. 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 Morani 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 U. S. 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 Morani 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 more flashy and popular government activities. Riccardo Morani 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 Morani 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.
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