Slowly-Collapsing Bridge Disrupts River Navigation in Dresden

 

A damaged and failing bridge briefly shut down inland shipping on the Elbe at Dresden last weekend, the second time in five months that barge traffic has been halted by the risk of falling concrete and steel. 

On September 11, 2024, at about 0300 hours in the morning, two spans of the Carola Bridge collapsed. A light-rail train had just gone by, but it was past and clear of the span, and no one was injured in the collapse. The bridge was one of four main crossings of the Elbe in downtown Dresden, and the loss of the span has been disruptive for businesses - and for shipping interests, which use the Elbe to access upriver regions as far as the Czech Republic (when water levels allow). 

The bridge was built under Communist rule in 1967-71. It had been inspected properly and passed all routine exams, according to Simone Pruefer, the head of the city's engineering office. "We were all very surprised," she told German media.

A post-accident study by the Institute of Concrete Structures at TU Dresden determined that the collapse was caused by hydrogen-induced stress corrosion of the bridge's steel components. This form of corrosion is nearly impossible to detect with conventional methods, the study concluded, as it affects steel elements that are hidden from view.  

The waterway was shut for four months for demolition and removal, a task made more challenging by the discovery of WWII-era bombs at the demolition site (common for Dresden, which was bombed heavily by Allied forces). Later testing revealed that the cause was hydrogen-induced stress corrosion. 

The surviving bridge spans have similar corrosion problems, and the surviving bridge spans will have to be completely demolished and rebuilt. To ensure safety of navigation in the interim, the city has installed acoustic monitoring systems. 

Last week, another prestressed steel component broke in the still-standing section of the bridge, prompting another temporary navigation shutdown. Every time the temperature fluctuates, it exerts stress on the surviving steel cables and raises the risk of another critical failure, bridge engineer Steffen Marx of TU Dresden told local media. The city has hired a contractor to complete the demolition of the rest of the bridge on an expedited basis, in hopes of finishing the job by the end of 2025. 

For now, ships are free to pass through during a limited two-hour slot from 0900 through 1100 hours each day. They must pre-register, and only necessary crew may be on board during the transit.