Normal Inspection Regime Could Not Have Anticipated German Bridge Fail

The collapse in September of a tram bridge in Dresden could not have been predicted by a usual inspection regime, according to the independent investigation.

Carola Bridge in September. Credit: City of Dresden

Professor Steffen Marx of the Institute of Structural Concrete at TU Dresden was commissioned by the state capital of Dresden to investigate the failure of Carola Bridge’s section C, which collapsed into the River Elbe on 11 September (link opens in new tab). Last week, he presented his interim report.

The investigation found that the cause of the collapse was hydrogen-induced stress corrosion cracking. This, along with material fatigue, led to the failure of tendons, with more than 68 percent of the tendons in section C severely damaged.

The water ingress which led to the corrosion damage would have happened while the bridge was under construction, back in the early 1970s. The investigation found chloride-induced corrosion, but the report did not attribute the collapse to this.

The investigation also found that the city of Dresden had inspected the bridge according to usual standards, and it had commissioned special reports. The report says that it wouldn’t have been possible to reliably predict the collapse through these methods.

The interim report also says that the bridge’s standing sections (termed A and B) can’t be put back into operation. They will be demolished and the bridge replaced.

The city is planning to clear section C out of the shipping channel by the end of the year. This week, it plans to install an acoustic monitoring system on sections A and B. This sound emission monitoring system will record in real time the condition of prestressed steel in sections A and B. By the middle of January 2025, this system will have generated enough data to allow the city to decide whether it is safe to permit navigation under these sections.