Complete demolition of the Carola Bridge in Dresden necessary

The partially collapsed Carola Bridge over the Elbe in Dresden will be completely demolished. According to experts, even the A and B lines for car traffic, which are not directly affected, are not safe. The city is now also planning to dismantle them and urgently needs a replacement.

The main reason for the failure of traffic line C was determined to be stress corrosion cracking caused by moisture. In conjunction with material fatigue caused by loading, preliminary findings indicate that this led to numerous tendons in the bridge failing and losing their tensioning force.

"Stress corrosion cracking was almost certainly the cause of the collapse," said bridge expert Steffen Marx from TU Dresden. This had a lot to do with the properties of the material, which was brought to the required strength with what is known as oil tempering. "The steel is drawn through a cold oil bath immediately after rolling." However, this can also lead to so-called embrittlement due to moisture. This serious consequence only became apparent at the end of the 1980s/beginning of the 1990s.

According to Marx, two thirds of the prestressing steel samples from the entire Carola Bridge had severe cracks. "If this is the case, the bridge has reached its expiration date," he said. The process could not be stopped, but would continue with use, and any measures would no longer be of any use. Corrosion damage to the prestressing steel used had already occurred during construction due to moisture caused by the weather and condensation.

Cracks already appeared during the construction of the Carola Bridge

Damage images on the tendons in the deck slab indicate that a significant proportion of the prestressing wires were no longer contributing to the load-bearing capacity of the structure over a long period of time. The experts assume that ultimately progressive prestressing steel failure at the heavily stressed cross-section in the pier axis D led to the failure.

On the night of September 11, around 100 meters of the still unrenovated western section of bridge C with streetcar tracks and cycle path collapsed unexpectedly. A few days later, the first debris was removed and since the beginning of October, the demolition of train C of the now closed important inner-city traffic artery has been underway. However, there is currently another pause due to flooding.

According to the investigations commissioned by the city to Professor Marx from the Institute for Solid Construction at TU Dresden, there were no sufficient signs that could have reliably predicted the collapse. For example, there was no pronounced crack formation due to the special construction. "Today we know that even very small cracks must be regarded as a criterion for damage and therefore an early warning."

Experts warn against further use of the bridge remains

In view of this, the experts warn against the reuse of bridges A and B, which have already been renovated. This is - even temporarily - "not justifiable and out of the question", said Marx. Findings from technical material investigations have also shown damage there as a result of stress corrosion cracking. The experts therefore see too high a risk that another sudden failure could occur without prior notice. The remaining bridge should no longer be loaded until it is dismantled in a controlled manner.

City wants a quick replacement - costs of over 100 million euros expected

According to a press release, the city is already examining the framework conditions of three variants of a new bridge, as Mayor Stephan Kühn (Greens) told the city council's construction committee this evening. The administration favors a simplified planning procedure - and assumes costs of no less than 100 million euros.

The experts certified to the city that the bridge was assessed and operated in accordance with the applicable regulations. "There is no evidence of negligent handling." Legal requirements were complied with, the structure was regularly inspected in accordance with the standards and specifically for risks, and recommendations for handling prestressed concrete bridges were implemented.