Government Europa speaks to Jürgen Krieger at BASt about the safety of Europe’s bridges, analysing specifically how Germany monitors the safety of its structures.
On 14 August 2018 the Ponte Morandi viaduct in Genoa collapsed, killing 43 people. The bridge was undergoing maintenance during the time of its collapse and the cause of the incident is said to be due to structural weakness and corrosion. Following the Genoa bridge collapse, reports into the structural soundness of bridges in a multitude of European countries have found that a worrying number of the flyovers connecting Europe are in detrimental or poor condition.
Very shortly after, an audit of the French government revealed that of the 12,000 state-maintained bridges spanning the country, a third are in need of repairs and 840 are at risk of collapsing. The issue does not lie solely in France; it is becoming a common occurrence across the whole of Europe.
In Germany, bridges are also ageing and the Federal Highway Research Institute (BASt) released a report in 2017 stating that 12.4 per cent of bridges were in poor condition. However, are these figures really as worrying as they initially sound? Government Europa speaks to Jürgen Krieger at BASt about what these figures actually mean and the relative safety of Germany’s bridges. Krieger highlights the thorough and positive inspection regime that Germany follows, including the surveying of each bridge every three years.
What are the causal factors of a weak bridge?
There are a number of different reasons as to why a bridge may become weak or collapse, with ageing being the most obvious. However, societal and environmental changes have also contributed to the decline of the stability of our bridges. Krieger says: “With regard to the findings in our report, new bridges have a better rating than older ones, and of course that is down to ageing. However, we are carrying out maintenance and refurbishment of our older bridges; without replacing all of our older bridges with new ones, this will always be the case.
“There are other factors which can affect the structural stability of a bridge, including a number of environmental impacts; we use a lot of de-icing salt on our roads, especially in the South and this can lead to road and bridge deterioration. In short, ageing is the biggest causal factor, however we must not overlook other societal and environmental impacts.
“Another consideration is a lack of funding and allocation of money to the specific maintenance of our roads and bridges. I believe that during the past 10 to 15 years, operators have not over exerted the amount of money placed on maintenance – this has changed now. The Ministry of Transport has noticed the lack of money being injected into the industry and has set aside a much higher budget in the hope to improve the condition of bridges and ensure we have access to more sophisticated asset management procedures.”
Detecting and repairing damage
Detecting weakness in a bridge is obviously crucial for measuring the stability and safety of the structure; you cannot repair damage that you have not found, and if you don’t correctly detect a weakness, catastrophe hits. But how do engineers detect damages within a structure? Krieger says: “Bridge inspection is carried out by certified engineers and although the inspection is visual, an engineer will be able to evaluate the severity of the damage by assessing the position or length of a crack, etc. These operations are carried out on every bridge every three years, meaning the bridges are constantly under surveillance.
“Should an engineer notice something unusual during the general inspection, then of course we proceed with more detailed inspections and we do have a second level which includes other technologies. If we do notice an issue with a specific bridge, we can also go to what we call Structural Health Monitoring. Here, detected weaknesses or damages of a structure are monitored online using special sensor technology (strain measurements, displacement measurements, acceleration measurements, temperature measurements, etc.) in order to detect any damage progress that may take place online.”
There are barriers to repairing and maintaining bridges and these barriers are in-line with the primary reason for structural degradation: traffic. Across the whole of Europe, we are seeing more congested roads and more cars and lorries are driving along our motorways every day. As well as wearing down the condition of the roads, the increase in traffic can make it difficult to work on them. Krieger explains: “We cannot shut down a motorway for a long period of time, it is just not feasible. With 150,000 vehicles on our roads every day, we cannot afford to stop journeys for repairs, this means that all maintenance work must be done under-traffic. To rebuild a bridge, we would need to submit a plan for approval, which is basically like starting right from the beginning; this can take many years to go through due to environmental impact assessments.”
Designing the modern bridge
Despite the emergence of a number of new building materials, Krieger points out that the process is more difficult than simply deciding to use a newly developed material. He points out that it is imperative that these materials be able to withstand the test of time and it can be difficult to measure how durable the material will be over a duration of 100 years. Krieger says: “During the last 20 to 50 years, the development of high-performance materials has rocketed and we are seeing so many more sophisticated designs. One practical example is in our road tunnels; we are using a specially designed concrete that offers greater fire protection and addresses some of the safety issues we have seen arise when using traditional concrete materials.
“On the other hand, the decision on whether to implement these materials is a difficult one, owners and governments have to be certain that new materials will perform to a high standard during the entire lifecycle of each structure – we design our bridges to last between 80 to 100 years. The difficulty here is that with new materials we cannot wait 50 years to implement them, but we also cannot just take the leap on a material that is not fully tested, we need to find a way to accelerate the testing and reviewing process of new developments to enable us to use them within our structures.”
The future of Germany’s bridge infrastructure
According to Krieger: “The future of our bridges relies on upgrading, replacing and refurbishing an ageing infrastructure. Our bridges are definitely safe, but of course we do need some time to bring our infrastructure up to the level where we would like it – we cannot simply replace every bridge with newer versions. We conduct bridge inspections and they undergo numerous assessments, therefore if we are worried about the safety of one of our bridges, necessary measures will be taken.”
Dr Jürgen Krieger
Head of Department Bridges and Structural Technology
Federal Highway Research