With a Hammer and a Good Ear—How Bridges Are Inspected

“Otherwise, the inspectors examine every square meter closely, looking for cracks, moisture penetration, and spalling,” adds Wirth. “This method has proven itself over the years.” The manual method has proven to be the most reliable. Attempts were made to take images with drones, but those would only provide pictures. “You simply don’t get that auditory feedback,” says the expert.

Inspection takes one day

The team needs about two hours to inspect the substructure of the roughly 30-meter-long bridge near Siebenlehn. Overall, the structural inspection is completed within a day. Disruptions for drivers remain minimal. The right lane is closed for the bridge inspection equipment—in one direction in the morning and the other in the afternoon. “We actually want to be gone by the time the evening rush hour starts,” says Wirth. 

Any damage found is initially monitored. During the inspections, the teams compare the condition to the most recent status report. Intervention is possible if cracks measure about 0.3 millimeters. They are then sealed with resin. “Otherwise, air and moisture can penetrate, and the steel will eventually start to rust,” explains Wirth. As part of the repairs, the rubber layers at the transition to the solid subgrade can also be replaced. In addition, moisture barriers or the roadway surface can be renewed.

Annual Inspections of Bridges from the GDR Era

Since the collapse of the Carolabrücke in Dresden, special attention has been paid to bridges from the GDR era that use Hennigsdorf prestressing steel. This steel is prone to stress corrosion cracking, which was identified as the cause of the collapse in Dresden.

There are also about ten such bridges along the highways; for example, several such structures span the A14 near Nossen. Since the collapse in Dresden two years ago, they have been inspected particularly thoroughly. “Instead of every three years as before, we now check annually to see if anything has changed,” says Wirth. 

“But these bridges aren’t as critical because they have a different design,” the expert emphasizes. Unlike the collapsed Carola Bridge, the tendons were cast directly into the precast concrete sections at the factory. This prevents pre-existing damage caused by moisture in the air during on-site installation. In addition, plates have been installed to distribute the load. “If a precast element were to fail, the load would be distributed to the right and left,” explains Wirth.

Bridge Demolition on the A14 Due to Increasing Damage

Nevertheless, two weeks ago, inspectors had to pull the emergency stop on an overpass spanning the A14 near Grimma. “It was in a critical condition,” says the expert. Longitudinal cracks had already been identified previously; during the inspection, these had increased significantly, and the inspectors also found the first transverse cracks. “Within a year, the cracks had widened from 0.5 to 1.5 millimeters—that was already a clear sign that something was happening inside the structure,” reports Bernhauser. 

It was already clear during the inspection that no traffic could pass over the bridge, which until then had connected the Grimma districts of Grottewitz and Würschwitz. Things moved quickly after that: The bridge was closed immediately. It took only one weekend to demolish the superstructure; the piers will remain standing for the time being.

• Link Autobahn GmbH

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