Why do bridges collapse – and how can we prevent it?

The Ponte Morandi bridge, Genoa, after its collapse, which has claimed dozens of lives. Image: Luca Zennaro/EPA.

As rescue workers look for survivors in the concrete rubble that used to be part of the Morandi bridge in Genoa, Italian authorities are starting their investigation into the possible causes behind this terrible tragedy.

It is too early to determine what may have caused the catastrophic collapse of more than 100 metres of the multi-span, cable-stayed suspension bridge, completed just over 50 years ago. But it’s important to understand that bridge engineering does not end when construction finishes and traffic starts to flow. In fact, properly looking after a bridge during its long life is as crucial as having a good design, using high-quality materials, and ensuring sound workmanship during construction.

Modern bridges are designed for a life of 100 years, though many centenarian bridges – such as the Forth Bridge in Scotland, which opened in 1890 – still provide sterling service, and of course there are smaller bridges built of stone to more ancient designs that have stood for many hundreds of years. Considering the number of bridges built in Europe during the expansion of the motorway networks from the late-1950s onwards, we should expect, and be prepared for, many to exceed their planned lifespan in coming decades. Facilitating this is ambitious but necessary, and made possible thanks only to regular inspection and maintenance that ensures that building materials have not degraded, and that structural elements are fit to bear the traffic and environmental loads they face.

The Forth Bridge outside Edinburgh, one of Britain’s iconic bridges, is more than 100 years old. Image: Andrew Shiva/The Conversation.

So what are the factors that affect the strength of a bridge and may compromise public safety?

Environment and climate

The climate in a bridge’s location, taken alongside atmospheric pollution common in cities, can have an adverse influence on the material of the bridge – for example, the corrosion of steel reinforcement or pre-stressed steel tendons embedded in concrete. Regular inspections are typically scheduled every six years for large bridges to identify any degradation, and to take appropriate measures to replace cracking concrete and corroded steel, or to introduce protective coatings.

In England, the Midlands Link motorway viaducts, comprising 13 miles of elevated motorway carrying the M5 and M6 motorways around Birmingham, suffered from chloride-induced steel corrosion early on in their life from exposure to salt used to de-ice the roads. This required an extensive application of corrosion protection measures in the early 1990s. More than 700 structures have benefited from this action, demonstrating the cost savings that can be made if appropriate action is taken at the right time.


Stress and fatigue

Fatigue caused by use is another factor, and inspectors will look out for tell-tale signs of failure often associated with the cyclical stress produced by passing vehicles, particularly heavy trucks. This type of failure is especially relevant for metal bridge decks and the cables of suspension and cable-stayed bridges. Traffic has increased ever since these bridges were built, which inevitably leads to the need for more maintenance and strengthening work, such as additional steel, glass or carbon fibre-reinforced plates on critical parts in order to restore or enhance their strength compared to what was deemed necessary during their design. For example, Network Rail in the UK used fibre-reinforced polymers to strengthen more than 20 bridges carrying highway or railway traffic between 2001 and 2010.

Consider how we all tend to react to a road sign bearing the words: “Essential Bridge Works – Expect Long Delays”. One such situation prompted this comment from a member of the public: “We are doomed. I am going to buy a tent and pitch it outside work for the three months while the misery goes on.” Perhaps knowing why this is necessary – and the consequences of not doing so – might persuade people to reconsider such views.

Money and willingness to spend it

Equally, we must understand that maintenance budgets need to be set at levels that far exceed those that would allow engineers only to “firefight” the most severe problems, as is becoming worryingly commonplace. Instead, budgets need to allow for planned interventions and necessary upgrades over many decades. That requires public and government support, as well as skilled engineers committed to ensuring the safety of an ageing structure.

There are challenges in devising improved methods to assess bridge strength, developing new repair techniques, and new ways of collecting and using inspection and monitoring data to provide advance warning of problems. These constantly push technological boundaries, making it possible to operate existing bridges safely during their long service lives. And the experience gained feeds into new designs that will become reality in years to come.

The ConversationThose investigating the collapse of the Morandi bridge will look at inspection and maintenance matters. Other lines of enquiry will no doubt include the unusual design of the multi-span bridge, with only a few cable stays to transfer deck loads to the towers, the ongoing work to shore up the foundations, and the heavy rainfall at the time of the collapse. In the shadow of this terrible loss of life, it is worth remembering that bridge inspection and maintenance may be annoying for commuters – but it is crucial.

Marios Chryssanthopoulos, Professor of Structural Systems, University of Surrey.

This article was originally published on The Conversation. Read the original article.

 
 
 
 

Barcelona’s car-free “superblocks” could extend lives. So will they catch on elsewhere?

Barcelona. Image: Getty.

The world’s biggest cities have larger populations and higher economic outputs than some countries. But as they grow in size and complexity, cities are also facing thorny challenges that threaten the health and happiness of residents. Congestion, pollution and a lack of community spaces have become major drags on people’s aspirations and experiences of urban living.

In response, cities must manage their resources and priorities to create sustainable places for visitors and residents, and foster innovation and growth. Enter Barcelona – the capital of Catalonia, in Spain – where a bold stroke of urban planning first introduced “superblocks” in 2016.

Image: ISGlobal/FAL.

Superblocks are neighbourhoods of nine blocks, where traffic is restricted to major roads around the outside, opening up entire groups of streets to pedestrians and cyclists. The aim is to reduce pollution from vehicles, and give residents much-needed relief from noise pollution. They are designed to create more open space for citizens to meet, talk and do activities.


Health and well-being boost

There are currently only six superblocks in operation, including the first, most prominent one in Eixample. Reports suggest that – despite some early push back – the change has been broadly welcomed by residents, and the long-term benefits could be considerable.

A recent study carried out by the Barcelona Institute for Global Health estimates that if, as planned, 503 potential superblocks are realised across the city, journeys by private vehicle would fall by 230,000 a week, as people switch to public transport, walking or cycling.

The research suggests this would significantly improve air quality and noise levels on the car-free streets: ambient levels of nitrogen dioxide (NO₂) would be reduced by a quarter, bringing levels in line with recommendations from the World Health Organisation (WHO).

The plan is also expected to generate significant health benefits for residents. The study estimates that as many as 667 premature deaths from air pollution, noise and heat could be prevented each year. More green spaces will encourage people to get outdoors and lead a more active lifestyle.

This, in turn, helps to reduce obesity and diabetes and ease pressure on health services. The researchers claim that residents of Barcelona could expect to live an extra 200 days thanks to the cumulative health benefits, if the idea is rolled out across the city.

Space to play. Imag: Mosa Moseneke/Unsplash.

There are expected to be benefits to mental health, as well as physical health. Having access to such spaces can stave off loneliness and isolation – especially among elderly residents – as communities form stronger bonds and become more resilient.

Stumbling blocks

It was Salvador Rueda, director of the Urban Ecology Agency of Barcelona, who first championed the introduction of superblocks – and he argues that the idea could be used in any city. Even so, authorities looking to expand the concept in Barcelona or beyond will need to be mindful of some concerns.

Changes like these require capital investment. Even as the car-free streets are transformed with urban furniture and greenery, the remaining major roads will likely have to accommodate heavier traffic.

Nothing comes for free. Image: Zvileve/Flickr/creative commons.

Further investments in local infrastructure – such as improving surrounding roads to deal with more traffic, or installing smart traffic management system – could be required to prevent serious congestion. Then the question remains, how to finance such investments – a higher tax rate is unlikely to be popular.


What’s more, whenever a location becomes more desirable, it leads to an increase in property demand. Higher prices and rent could create pockets of unaffordable neighbourhoods. This may lead to use of properties for investment purposes and possibly, displacement of local residents.

It’s also worth noting that Barcelona is an old and relatively well-planned European city. Different challenges exist in emerging global cities across Asia, Africa and Latin America – and in younger cities in the US and Australia. There is a great deal of variation in scale, population density, urban shape and form, development patterns and institutional frameworks across the cities. Several large cities in the developing world are heavily congested with uncontrolled, unregulated developments and weak regulatory frameworks.

Replicating what’s been done in Barcelona may prove difficult in such places, and will require much greater transformations. But it’s true that the basic principles of superblocks – that value pedestrians, cyclists and high quality public spaces over motor vehicles – can be applied in any city, with some adjustments.

Leading the way

Over the history of human civilisation, great cities have been at the forefront of innovation and social progress. But cities need a robust structure of governance, which is transparent and accountable, to ensure a fair and efficient use of resources. Imposing innovation from the top down, without consultations and buy-in, can go squarely against the idea of free market capitalism, which has been a predominant force for modern economies and can lead push-back from citizens and local businesses.

Citizens must also be willing to change their perspectives and behaviour, to make such initiatives work. This means that “solutions” to urban living like superblocks need to have buy-in from citizens, through continuous engagement with local government officials.

A man speaks at a public consultation on the Eixample superblock in Barcelona. Image: Ajuntament Barcelona/Flickr/creative commons.

Successful urban planning also needs strong leadership with a clear and consistent vision of the future, and a roadmap of how that vision can be delivered. The vision should be co-developed with the citizens and all other stakeholders such as local businesses, private and public organisations. This can ensure that everybody shares ownership and takes responsibility for the success of local initiatives.

There is little doubt that the principles and objectives of superblocks are sound. The idea has the potential to catch on around the world – though it will likely take a unique and specific form in every city.

The Conversation

Anupam Nanda, Professor of Urban Economics and Real Estate, University of Reading.

This article is republished from The Conversation under a Creative Commons license. Read the original article.