A partial collapse of the Morandi bridge in Genoa, Italy has led so far to the deaths of 37 people after their vehicles fell from the wrecked structure.
An approximately 210m long section of the Morandi bridge collapsed yesterday, August 14, 2018, at 11.30, injuring a further 16 people. Members of the Italian Red Cross are using sniffer dogs to find people trapped in the wreckage.
The bridge, which is part of the Polcevera Creek Viaduct, was built in a densely crowded urban area occupied by two railroad yards and large industrial facilities. The structure, designed by Riccardo Morandi, was opened in 1967 and was said to be undergoing structural repairs at the time of collapse.
According to Dr Maria Rosaria Marsico, senior lecturer in structural engineering at Exeter University, the viaduct includes three cable-stayed spans and a series of minor spans for a total length of about 1182m. The three largest spans consist of independent cable-stayed structures, each carried by an individual reinforced concrete pier and tower 90m high.
“The cable-stayed systems were characterised by the adoption of prestressed concrete stays, a common feature of bridges designed by Morandi in the sixties,” she said. “The viaduct was subject to maintenance work since it was built, and in the nineties a complex intervention of repair was carried out involving the installation of conventional steel tendons which are flanking the existing concrete stays.”
Ian Firth, FREng, past president of The Institution of Structural Engineers, said it is too early to say what caused the collapse of Morandi bridge, but corrosion of tendons or reinforcement may be a contributory factor given the age of the bridge.
According to recent research, corrosion of reinforcement changes the long-term behaviour of ageing reinforced concrete bridges, said Dr Mehdi Kashani, associate professor in structural mechanics at Southampton University.
“In addition, bridges are constantly subjected to cyclic dynamic loading due to highway traffic, wind and/or major/minor earthquake, which will result in fatigue damage in bridge components,” said Dr Kashani. “It is reported that this bridge collapsed during a heavy storm. Therefore, dynamic wind loading, combined with additional loading due to on-going work on the bridge, and reduced capacity due to corrosion and fatigue might be the cause of failure. However, there is need for further detailed investigation to fully understand the cause of failure.”
Firth said the A-frame towers which support the concrete-encased stay cables combine with V-shaped supports below the deck of the bridge to create a stiff arrangement which is not common in cable-stayed bridges.
“This deals with potential unbalanced loads which arise due to the multi-span nature of the structure,” he said. “As yet, there is no evidence to say whether any impact occurred; it is too early to say what triggered the collapse.”