Dresden experts: Check the risk of similar bridges

The cause of the collapse of Dresden's Carola Bridge, as determined by experts, can also have fatal consequences for comparable prestressed concrete bridges. Such structures must be intensively tested in future, said bridge expert Steffen Marx from TU Dresden. Samples can be used to determine whether the prestressing steel used is a high-risk material, and the acoustic emission method can be used to determine whether stress corrosion cracking is really taking place. "If not, the bridge can continue to be operated safely for years to come."

Around 1,000 bridges nationwide with this material

According to Marx, there are around 1,000 bridges nationwide in which this special prestressing steel has been used as a material. A cold oil bath immediately after rolling made it particularly strong, but can also lead to so-called embrittlement, he explained. Half an hour of moisture is then enough for cracks to form. The process of their propagation and eventual failure of the prestressing steel can take years, without any externally visible traces.

According to Marx, this "serious" consequence became apparent in the late 1980s/early 1990s with the collapse of the Berlin congress hall known as the "pregnant oyster" or a factory building in Mannheim. This is because this steel, which had not been produced for years, was also produced and used in the West.

Acoustic emission method shows problem quite reliably

The acoustic emission method has also been usable in bridge construction since 2010, but has only rarely been used in Germany so far "because it is very expensive", said Marx. As a consequence of the surprising collapse of the Carola Bridge in Dresden, his team is currently developing a risk catalog for such bridges. "There were very small cracks, less than 0.1 millimetres, which were already found in the 1990s but were attributed to other causes," he said. In addition, cracks up to 0.2 millimetres were not considered critical.

This is now different. According to Marx, the demolition concept must now also be subordinated to the fact that every load movement is one too many. "The bridge is still in acute danger of collapse."