Bridge collapse in italy – expert reaction – science media centre

“It is too early to say what caused the tragic collapse, but as this reinforced and prestressed concrete bridge has been there for 50 years it is possible that corrosion of tendons or reinforcement may be a contributory factor. There are no obvious signs to say what specifically triggered the collapse at this time; the fact that there was reported to be a storm at the time may or may not be particularly relevant. In addition, on-going work on the bridge may or may not be partly responsible for the collapse.

“The bridge is a very unusual design, very similar to its much larger cousin, the Lake Maracaibo bridge in Venezuela, also designed by Riccardo Morandi and completed 6 years earlier in 1962. The A-frame towers which support the concrete-encased stay cables combine with V-shaped supports below the deck 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. As yet, there is no evidence to say whether any impact occurred; it is too early to say what triggered the collapse.”

“At this stage it is very difficult to make a solid judgement on the cause of this catastrophic collapse. The bridge was constructed using reinforced and pre-stressed concrete about 50 years ago. There are a large number of reinforced concrete bridges in Italy, Europe, USA, and Canada with the same age, which are suffering from corrosion of reinforcement and/or pre-stressing tendon.

“Recent research showed that corrosion of reinforcement changes the long-term behaviour of ageing reinforced concrete bridges. In addition, bridges are constantly subjected to cyclic dynamic loading due highway traffic, wind and/or major/minor earthquake, which will result in fatigue damage in bridge components. 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 bride, and reduced capacity due to corrosion and fatigue might be the cause of failure. However, there is a need for further detailed investigation to fully understand the cause of failure.

“Whilst it is perhaps not impossible to think that a lightning strike makes a contribution to such a collapse, it is probably very unlikely to happen. Lightning could potentially contribute to a critical fatigue of material. For example, the lightning generated heat could result in evaporating water to very high pressure and produce a subsequent crack or burst of critical support material, similar to the bark of a tree disintegrating after a lightning strike. In theory, in might be also possible that the lightning strikes a critical metal bolt such that its function becomes impaired. But again, any such kind of scenarios are rather speculative.”

“The most important is to follow the guidelines for lightning protection as set out by the standardising institution in the respective country. These guidelines are normally based on the long term experience with lightning damage and take into account scientific evidence that is constantly updated, based on new knowledge that is generated. In this extreme case, a careful investigation of what might have happened seems to be particularly important to avoid similar scenarios in the future.”

“It is too early to comment on the causes of this tragedy, and in respect of the victims and their families speculations should be avoided until scientific evidences are gathered. The bridge that collapsed today is part of the Polcevera Creek Viaduct in Genoa, Italy. It was built in a densely crowded urban area which is occupied by two railroad yards, large industrial plants and the Polcevera Creek. The bridge is known as Morandi Bridge from its designer, the engineer Riccardo Morandi. Its construction started in 1963 and was completed in 1967 when it was opened.

“It was a beautiful expression of the engineering design. The viaduct includes three cable-stayed spans and a series of minor spans for a total length of about 1182 m. The three largest spans consist of independent cable-stayed structures, each carried by an individual reinforced concrete pier and tower 90 m high. The longest span that collapsed today was about 210 m long. The cable-stayed systems was characterised by the adoption of prestressed concrete stays, a common feature of bridges designed by R. Morandi in the sixties 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.”

“Aging infrastructure and its impact on structural integrity and safety should become of prime concern to structural engineers. The potential impact of the environment and extreme weather conditions (possibly associated with climate change) also needs to be assessed. The need for monitoring structural performance, understanding the causes of the exhibited collapse and developing reliable assessment methods is essential so that events like this be avoided in the future.”

“The causes of this tragedy are yet to be uncovered. But uncovered they shall be by skilled structural engineers who will look for tale-tell signs of initiation of failure. It is of no comfort to today’s victims and their families, but the reality is that the beautiful, enormous bridge structures we see all over the world stand safely due to the extraordinary abilities of structural engineers. It is when we are hit by such tragedy, thankfully so rarely, that we realise just how important the work of these engineers really is.”