August 14, 2018

expert reaction to Genoa motorway bridge collapse

A motorway bridge in Genoa in Italy has collapsed, killing a number of people.

Prof Daniele Zonta, Department of Civil and Environmental Engineering at the University of Strathclyde, said:

“It is largely premature to speculate on the causes of the Morandi Bridge collapse, but it is likely that its state of preservation of its concrete tendons will be deeply analysed in the forthcoming forensic investigation.

“Completed in 1968, the bridge dates back to the pioneering age of pre-stressed reinforced concrete in Italy, and is one of the most iconic engineering work by Riccardo Morandi.

“Its longest spans are supported by pre-stressed concrete tendons instead of the more common steel cables, an innovative and peculiar design choice, favoured by Morandi but rarely adopted elsewhere.

“Since its construction, the deterioration of the concrete tendons has been a major source of concern, requiring continuous monitoring and maintenance. A radical repair was carried out in the 1990s and is still clearly visible on the four stays of the easternmost standing tower.

“Its state of deterioration was notorious, to the point that the bridge is typically used as a handbook example in Italian structural engineering classes. Exactly for this reason, the bridge was supposedly well maintained and continuously supervised, and the tragic news of its collapse is completely unexpected.”

Dr Maria Rosaria Marsico, senior lecturer in Structural Engineering at the University of Exeter, said:

“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 characterized 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.”

Based on speculation in some reports about a lightning strike, Dr Martin Fullekrug, Reader in the University of Bath’s Department of Electronic & Electrical Engineering, said:

How powerful is lightning?

“Very often, it is quoted that lightning can be as powerful as a nuclear power plant. Yet, it is normally not pointed out that this power only takes effect over an extremely short amount of time, typically just a few tens of a millionth of a second, such that the impact of lightning often remains quite limited.

What sort of damage can it cause?

“Lightning often has indirect effects, such as on consumer electronics when it strikes unprotected buildings. However, in the worst case, it can also have direct effects such as melting metal, ignite forest fires and kill people, animal herds and trees.

Could a lightning strike cause a structure such as a concrete bridge to collapse?

“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.

What sort of things can be done to structures to mitigate damage from lightning strikes?

“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.”

Dr Mehdi Kashani, Associate Professor in Structural Mechanics, University of Southampton, said:

“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 need for further detailed investigation to fully understand the cause of failure. The bridge engineering research community should take this seriously in their future research to improve the resilience of our infrastructure under extreme loading.”

Dr Demitrios Cotsovos, Associate Professor, Institute of Infrastructure and Environment, Heriot-Watt University, said:

“This is tragic event. One should consider all possibilities before drawing any conclusions. It is important to investigate in detail the reasons that have led to such a catastrophic collapse. Potentially, there are lessons to be learnt from such an event. 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.”

Tim Ibell FREng, Professor of Civil Engineering, University of Bath, said:

“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.”

Prof Gordon Masterton FREng, Chair of Future Infrastructure, School of Engineering, University of Edinburgh, said:

“This is a terrible and tragic event and needs to be investigated thoroughly and forensically, gathering the best engineering minds available to ensure that the root cause is identified. Only then can there be any confidence on the likely trigger and sequence of events. Until that detailed inquiry, we really should not be speculating. There are several potential triggers for what appears to have happened and until more evidence is obtained from the debris, the eye witness accounts and the videos, it is unproductive and disrespectful to speculate as to whether one is more likely than the others.“

Ian Firth FREng, Consultant Structural Engineer at COWI and Past President of The Institution of Structural Engineers, said:

“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.”

Declared interests

None received.