Tragic news of a bridge collapse arrived this morning from Genoa, Italy: at least 20 were killed when an 80-metre section of the Polcevera Bridge on the A10 motorway came down during a storm. While the exact causes have still to be ascertained, the collapse is probably to be attributed to a system patented by engineer Riccardo Morandi.
Born in Rome in 1902, Morandi founded his own office when he was in his late twenties and started working closely with construction companies. Fascinated by the technology of concreting, he focused his career on concrete cable-stayed bridges.
The concrete stays of cable strayed bridges consist of pre-stressing tendons cast into a beam as thick concrete cover for corrosion protection. The stays are then post-tensioned so that they remain in compression.
The tie sections of Morandi's bridges were his trademark: though complicated, the ties behaved like a system made of tendons that worked in tension, and of a prestressed concrete case that worked instead in decompression under the traffic load.
Morandi taught bridge construction in Florence and in Rome between the late '50s and the early '70s. His name is linked with famous bridges in Maracaibo, Magliana, Polcevera, Wadi Kuf, Rio Magdalena and Carpineto, structures filed under the "brutalism" category that won him comparisons with works by Pier Luigi Nervi or Sergio Musmeci.
Built between 1960-64 and put in service in September 1967, the Polcevera bridge connected the A7 Genoa-Serravalle highway to the A10 Genoa-Ventimiglia highway, running over shopping centres, factories and homes.
It was a difficult construction that required long studies on proportions: three A-shaped frames characterised the main part of the bridge that featured supporting decks connected by suspended girders. The long decks were suspended to prestressed concrete ties at a distance of 10 metres from the ends of the girders. The Polcevera bridge was similar in its structure to the Maracaibo, Wadi Kuf and Rio Magdalena bridges. When it was finished the 90 metre high and 1km long Polcevera bridge was considered as a new and experimental design, but time wasn't kind on the system behind it.
Indeed, twenty-five years after it was opened (a relatively short span of time for a bridge) the system had to be serviced as the ties showed corrosion traces and there were minor damages around the tendons. Morandi's aide at the time of building Polcevera, Francesco Pisani, carried out the recovery program in the '90s and planned the repairing intervention phases. Each tie was flanked with a set of 12 modern cables so that the suspension action was transferred from the ties to the stays. The original design behaviour of the bridge was maintained avoiding changes in the deflection and flexural behaviour of the deck.
Prestressed concrete ties are not considered safe solutions in our modern days as the tie suspension action is entrusted to a limited number of elements, the structure is not so robust and the maintenance actions difficult. Nowadays bridges are therefore built with a great number of stays so that when one stays fauls the other suspension elements guarantee the maintenance operations to the cables and make the substitution operation easier.
In the case of the Polcevera bridge there was something else to consider: the structure went through a series of restructuring stages in recent years, but Italian engineer Antonio Brencich, Associate Professor in Concrete Structures at the Genoa University, already stated two years ago in an article on an engineering magazine that the precompression system patented by Morandi was a failure (also the Maracaibo bridge fell, but, in that case, it was hit by an oil tanker in 1964) and that the Polcevera bridge was in a critical condition due to corrosion. It was disappointing to discover that design-wise the system was not as reliable as it was supposed to be, but it was extremely sad to realise that a tragedy may have been avoided if the authorities had taken into consideration the opinion of an expert and if a few political parties (some of them leading the Italian government at the moment) hadn't considered the possibility of the bridge collapsing as an alarming but improbable silly story.
To ponder a bit more about the main theme of this post - brutalism that turns brutal - we're closing this piece with a special playlist inspired by brutalist architecture. Hopefully, it will make some of us stop and think about our cities and the way we interact with the urban environments surrounding us.
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