lose by the little German village of Eichenzell-Döllbach just south of Fulda, a roughly 20-meter-high highway bridge spans the Thalaubach stream, a road and several dirt tracks. Supported by 12 solid pillars of light-colored concrete and with a steel superstructure painted in blue, the bridge measuring some 300 meters appears sturdy. But looks can be deceiving.
The Thalaubach viaduct was opened to traffic in 1968 as part of the Rhönlinie route. While at that time, this section of highway ran through the economically underdeveloped area of former West Germany that bordered on East Germany, today, it forms part of the A 7 highway. When the highway was planned in 1959, traffic volumes were predicted to reach 17,000 vehicles per day in 1980. In reality, the figure was over 23,000 then – and had already risen to as many as 56,500 vehicles per day by 2015. This heavy-duty toll has made the steel structure brittle. Having reached the end of its life cycle, the bridge needs to be replaced in the next few years. Until then, it is critical to closely monitor the structure and respond immediately to any signs of damage.
To ensure that the bridge is kept under continual surveillance, those responsible at Hessen Mobil, the regional road and traffic management authority, decided to make use of an innovative solution offered by Bilfinger Noell in 2017. Acoustic emission testing is a tried and trusted measuring technology in many industries. The Bilfinger Noell experts have fine-tuned the technology to promptly detect and precisely locate any defects that start to form on bridges. Every hairline crack in a weld or minute change in the structure’s fabric results in acoustic emissions. Sensors positioned at strategic points on the bridge provide data for round-the-clock assessment by a software program. Serious changes trigger an alarm, allowing Hessen Mobil to respond instantly to any damage sustained – including, if necessary, completely closing the highway.
Measuring acoustic emissions is an innovative and reliable method of monitoring bridges. It generates significant value added for operators and is now also being used on the Salzbachtal bridge near Wiesbaden. Additionally, the technology is suitable for monitoring tunnels, other structures and machinery.