Open fade from black, show bridge pre collapse, angle 1 show collapse angle 2 show collapse
fade to black.
It is the 3rd of august 2020, and Italian President Sergio Mattarella is inaugurating
a new bridge in Genoa Italy.
The year has been a roller coaster of ups and downs, but the event marks a moment of
hope in the city’s history, many looking at the new bridge shed a tear.
But these emotions aren’t linked to the global pandemic but to an event 2 years before.
Mattarella isn't the first president to inaugurate a bridge on this site; that honor goes back
to 1967 with the completion of this bridge's fore runner, the Ponte Morandi.
The Morandi bridge, so named after its designer engineer Riccardo Morandi, met a tragic end
in august 2018, which would raise questions about vital infrastructure throughout Italy
and Europe as a whole.
Today’s video is about the story of this once engineering and architectural wonder
and it’s quite literal downfall.
////
Background
Our story starts not in the baking hot sun of Genoa Italy, but that of western Venezuela.
Engineer Riccardo Morandi had begun to pen a new bridge in 1957, this structure would
become a signature of sorts.
Morandi liked to design his bridges to look simple yet elegant, as such his General Rafael
Urdaneta Bridge, a cable stayed design used as few as only two stays per span.
Although striking in looks this has a number of drawbacks and that is of redundancy, less
stays equals more stress on the cables and thus less redundancy as the weight of the
structure is spread over a smaller area, a failure of 1 of the stays can result in too
much strain on the other, and thus makes a single point failure more likely.
The bridge was completed in 1962 and opened by president Rómulo Ernesto Betancourt Bello.
Well so pleased with the bridge was morandi that he decided to do the old control c control
v trick when he was asked to design a new structure back in Italy.
The bridge Viadotto Polcevera
Morandi's concept was selected for the design for the new Bridge which was to span the polcevera
valley, in Genoa.
It would carry the new A10 motorway through the city.
The new bridges design would Have a length of 1,182 meters (3,878 ft), a height above
the valley of 45 meters (148 ft) at road level, and three towering reinforced concrete pylons
reaching 90 meters (300 ft) in height; the maximum span was 210 meters (690 ft).
Like his previous bridge this one would use cable stays, but unlike the General Rafael
Urdaneta Bridge, they would be 52 cables bundled together encased in a post-tensioned concrete
shell.
At the time the cable coating was boasted as maintenance free and impervious to environmental
elements that could rust the vital stays.
But it would also obscure the vital cables, making inspection for damage virtually impossible.
Due to the extensive use of concrete the bridge had minimal use of steel, something vital
in post war Italy, where resources especially in steel production were limited due to international
sanctions.
Although a beautiful and clean looking design not a lot of thought was given to future traffic
volumes and thus its lifetime durability.
This feels very similar to the silver bridge, well spoiler alert cars and trucks would gain
weight over the years and the concrete protections of the stays wouldn’t actually stop corrosion.
The deck was made almost entirely of reinforced concrete, further reducing its metal use age.
Construction began in 1963 and was undertaken by Società Italiana per Condotte d'Acqua
SpA.
It was completed to great fanfare in 1969, and opened by president Giuseppe Saragat
.At the time of opening the bridge met the specifications set out by the government,
and it was thought to have an intended 50 year lifespan.
The bridge troubled from the start
Almost as soon as the pointe morandi opened to traffic the sleek and simple design proved
to be a costly structure to maintain.
You see when the concrete was originally laid the calculations for concrete creep were incorrect,
and as such shrinkage exceeded expectations resulting in an uneven and undulating roadway.
This would require a decade of remediation works, but this was not the only issue, you
know the apparently safe from the environment cabale stays well, they weren't so safe, as
the concrete began to deteriorate.
The issues with the bridge's concrete parts, which was most of it, were exacerbated by
the salty sea air and pollution from the industrial areas of the city.
By 1979 the bridge had deteriorated to a point that even Moriani himself needed to investigate
the structure.
Meanwhile the bridge in venezuela was beginning to show signs of age and with several of its
cables corroding, replacement was essential, but because of the design this proved to be
difficult.
As noted in an AMERICAN SOCIETY OF CIVIL ENGINEERS article.
“As the original design consisted of two layers of suspension cables passing over each
of the six main towers, replacing the cables without damaging the structure seemed nearly
impossible, given time and cost constraints.”
But one difference between the two sister bridges was that the Genoa bridge’s stays
were covered and thus hiding the warning signs of corrosion.
Back to Moriandi’s investigation into the bridge in 1979, he found cracks and issues
with the concrete structure degrading.
In his report of the same year, morandi would say himself,
"To remove all traces of rust on the exposure of the reinforcements, fill the patches with
epoxy resin, and cover everything up with an elastomer of very high chemical resistance".
All during the 1980s the cables on the bridge deteriorated still hidden from view, in the
early 90’s, pylon 11 the easternmost of the three main towers was investigated and
it was found that roughly 30% of the steel tendons had experienced corrosion, so much
so that it was thought they were only able to carry half their design weight.
To add more fuel to the fire vehicles continued to increase in weight and commercial trucks
went from something like this in the 1960s to something like this in the 1990s.
The affected areas were refurbished in a similar fashion to the General Rafael Urdaneta Bridge
as well having reinforcing cabales attached.
Pier 10 had the stays reinforced at the top, but this was the only remediation work on
the troublesome steel cables.
Autostrade per l'Italia took over management of the bridge in 1999, but no more work was
undertaken on repairing the rusted out strands.
As the new millennium came and the bridge was becoming increasingly congested, a replacement
was put on the books, but this would take time and more importantly money.
And thus the years ticked on, and warnings over the structure's reliability continued
to mount, government officials were told that the Morandi bridge needed maintenance.
Autostrade commissioned a report into the condition of the bridge in october 2017, from
Carmelo Gentile and Antonello Ruccolo of the Polytechnic University of Milan.
Over four nights, Professor Gentile recorded the frequencies of the Morandi bridge; a smooth
waveform would hint at a healthy structure, but when he tested the stays on tower 9 he
heard something worrying.
The findings of the university team hinted towards the stays rusting inside their concrete
enclosures.
During 2018 the bridge was receiving more substantial central concrete dividers, adding
considerable weight to the already weakened bridge.
On 3 May 2018 as the bridge was in its 51st year of existence, Autostrade announced a
tender for structural upgrades of the viaduct with a cost of €20,159,000, but this would
be too late.
The disaster.
It is the late morning of 14 August 2018, and cars are making their way across the Viadotto
Polcevera, the day has been marred with torrential rain.
At around 11:36 a 210 meter long section of the bridge around pylon 9 catastrophically
and suddenly failed.
Around 30 cars and 3 trucks were on the span that disappeared into the Polcevera valley
and Turin–Genoa and Milan–Genoa railways below.
The failure point as seen by cctv and witnesses was the southern stays, 43 people were lost
that morning with many more injured and at least 13 more missing.
Because the bridge navigated over and around residential areas, all property nearby was
evacuated, for fears of the remaining spans collapsing.
But remarkably the remaining sections remained.
One such story of pure luck was of a Damonte Trasporti S.R.L truck narrowly missing the
plunge the now iconic volvo titered on the edge, and became a symbol of the disaster.
Locals and emergency workers alike scrambled through the rubble to locate victims as they
called out from what used to be the bridge.
But with such a catastrophic collapse, claiming many lives, authorities had to find out what
was the cause of the ponte morandi collapse.
The cause
The bridges designer Moriandi was one person that athuritories would have liked to talk
to but unfortunately he had been dead for nearly 30 years, instead his design, notes
and surveys of the bridge were combed through to build up a picture of the structure.
in a case of perfect timing Riccardo Morandi’s design lasted almost exactly 51 years, hinting
he knew how to build to the expected lifespan of 50 years.
The design, which like many other striking simplistic designs, looked beautiful in exchange
for reduced redundancy and increased maintenance.
Now the point of failure is not difficult to find out as we have so much information
and footage both before, during and after the collapse.
We also know that the bridge and many similar designs from morandi had exhibited similar
issue, the General Rafael Urdaneta Bridge had in the late 70’s nearly collapsed due
to corrosion afterall.
Pylon 9 was the only one of the 3 main towers which held up the strands, to have not had
any proper remediation work, and was the most concerning during the 2017 Polytechnic University
of Milan report.
Straight away the newly elected government pointed the finger at Autostrade, but the
root cause was more than that, as the bridge right from its opening days had drained resources
just to keep open.
In the 467-page paper, investigating the cause of the collapse, many theories were explored
including excessive winds, which was put forward by Autostrade, these were discounted, as most
warning signs pointed towards the pesky concrete covered cable stays.
It was discovered that Moriandi himself, concerned about this design choice, had recommended
regular checks on the cables, checks that were never undertaken.
During the 90’s when the bridge was still under state control the concrete water resistance
had come into question, these concerns were passed onto the private operator Autostrade,
which were subsequently not investigated.
Engineers had suggested annual maintenance and frequent inspections of the aging bridge,
but, according to the official investigation, inspection did not come until 2012.
Nearly 20 years after the bridges last proper overhaul which strengthened tower 11 and parts
of tower 10, funnily enough the two that didn't fail.
Such was the perceived negligence of the private operator that it would turn into a criminal
case against 59 employees of Autostrade and its contractor Spea engineering company.
We won't know the outcome of that trial yet as at the time of working on this video august
2022 has only just begun.
The city was in shock, and the remains of the bridge acted as a grim headstone for those
lost, but tragedy would give way to pragmatism, there was the need of a crossing in the area,
and as such the decision to demolish the remains of the ponte morandi was made to make way
for a new and hopefully safer crossing.
The remains of the bridge was demolished in June 2019, and in almost record time a replacement
was built.
And that leads us back to 3rd of august 2020 almost 3 years to the day and the opening
of the new Genoa-Saint George Bridge.
Costing € 202 million the new bridge offers a new hope, but the issues concerning italian
and the wider european and uk community's infrastructure still exist, you see much like
many other subjects this channel covers it always boils down to money, and the risks
of underinvestment.
All videos on the channel are creative commons Attribution-ShareAlike.
Plainly difficult videos are produced by me John, in a wet and windy suburban Southeast
corner of London, uk.
Help the channel grow by liking commenting and subscribing!
Check out my twitter for all sorts of photos and odd and sods, as well as hints on future
videos!
I've got patreon and youtube membership as well so if you fancy check them out!
All that's left to say is thank you for watching!
https://www.pci.org/PCI_Docs/Publications/PCI%20Journal/1973/January-1973/Cable-Stayed%20Bridges%20of%20Prestressed%20Concrete.pdf
http://archplanbaltimore.blogspot.com/2020/08/disaster-recovery-success-and-role-of.html
https://webapi.ingenio-web.it/immagini/file/byname?name=riccardo-morandi-durabilita-ponte-pp.pdf
https://cedb.asce.org/CEDBsearch/record.jsp?dockey=0034749