New Civil Engineer exclusively reveals a 1960s report detailing the construction methods and designs behind the collapsed Morandi bridge in Genoa.
A search and rescue effort is still ongoing in Genoa after an approximately 250m long section of the 11 span, pre-stressed concrete, cable stayed motorway bridge collapsed, killing at least 35 people.
The 1965 report, obtained by New Civil Engineer, details the unusual structure’s key elements and the construction techniques used to build it. It also provides real insight into the construction itself through a series of photographs charting construction progress and will likely be used in future investigations into the collapse.
It explains how designer Riccardo Morandi viewed the single stay cable more as a reinforced concrete tie beam, with the steel tendons encased in concrete. The deck was constructed as a balanced cantilever with temporary tie beams running 1m above the deck providing temporary support until the permanent tie beam was constructed.
It also details the construction of the Morandi bridge’s foundations which highways operator Autostrade were carrying out works on at the time of collapse.
The report details how each of the main piers is founded on a reinforced concrete pile cap, which is in turn supported on large diameter bored piles, in many cases about 40m deep.
Temporary tie beams
“After casting the foundation piles and the pile caps, pier trestles and spars were constructed by traditional measures, using metal moulds and tubular framework,” the Viadotto sul Polcevera per l’Autrostrada Genova-Savona report outlines.
One theory mooted by engineers is that the heavy rainfall from the storm may have washed ground away from underneath the tower, undermining its foundation and causing the base of the tower to rotate and collapse.
However, New Civil Engineer’s founding editor Sydney Lenssen believes that there may be other factors at play.
Lenssen obtained the report during a visit to the Morandi bridge mid-construction in April 1965, in an organised tour promoting the use of concrete in long-span bridge construction. Lenssen said that there were several “unusual” structural design elements which may have contributed to the bridge’s collapse.
“At first look it doesn’t look like a fault in the foundations,” Lenssen told New Civil Engineer. “It appears to me that the structure has fallen down from above. So it looks like the structure has collapsed around the foundations, rather than the foundations causing the collapse.
“I suspect that one of the supports from underneath has given away. That or the cables above have suffered from corrosion.”
Lenssen, who previously worked as a structural engineer, added: “Morandi was convinced that covering the steel cables would protect them but it looked very strange. The concrete casing was also built in two or three sections and I was straight away concerned how this would protect the cables from corrosion.
“All suspension bridge cables suffer from corrosion, regardless of whether or not they are covered in concrete.”
Despite his reservations about the “unusual design”, Lenssen said that Morandi’s ambition was infectious and he was heralded as a genius at the time.
“Morandi was a bit of a genius and a very good businessman. At the time it was a terrifically ambitious structure, however strange the design was,” Lenssen said.
“There’s no doubt that it was an unusual design. It was a highly unusual structure, almost a mix match of bridge types.
“It wasn’t a cable stay bridge even though it had cables, it wasn’t a typical cantilever bridge either and it had a lot of supports between the structures.”
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