Carola Bridge instructive for dealing with such structures

The final report on the cause of the collapse of Dresden's Carola Bridge confirms the experts' previous assumptions. The cause was specific and not characteristic of prestressed concrete structures of this type in Germany, said Professor Steffen Marx from TU Dresden. According to him, cracks in the tendons were responsible for the collapse, which had been caused by sulphurous acid and had increased in size over time due to stress. The core "had been deeply embedded in this prestressing steel ever since".

As the Carola Bridge was well maintained and monitored, the cracks had been seen. However, the structural inspectors classified them as non-critical, as they were within the normal range. In this respect, the Carola Bridge was "not actually characteristic of the maintenance deficiencies that exist in Germany", said Marx. "They didn't exist here, at most minor marginal things."

Risk assessment instead of rapid demolition

According to Marx, the only thing that can be used to hear whether and where something is happening is the noise emission measurement. "This is also very good news for the many other bridges with this risk in Germany." This makes it possible to determine whether an active damage process is underway. On the rest of the Carola Bridge, there have been at least 20 fractures in the still-standing trains A and B since the beginning of the year.

As the technology for this method is expensive, the experts suggest that a risk assessment should first be carried out for other structures of this type. Marx estimates that over 1,000 bridges across Germany could be considered for this. Monitoring is a safer and cheaper method than a quick demolition and costs around 0.5 to 1 percent of a new construction sum.

"If it is possible to fish out the critical cases and only then demolish them, this would be a sensible economic and safety-oriented approach," said Marx. According to his estimate, there are perhaps 20 percent high-risk cases. "In the end, that leaves one percent where it is really critical."