Kistler Group (Switzerland) - Bridges are highly sensitive structures with a limited service life, which is why it is essential to monitor them in a targeted manner and maintain them at regular intervals. But how exactly is a road traffic or railway bridge monitored? Kistler experts Christoph Klauser, Business Development Manager Traffic Solutions, and Thomas Wuhrmann, Head of the Innovation Lab, explain in an interview what the greatest challenges facing bridges are, what data Kistler can collect and analyze with its measuring systems, and what a Digital Hub has to do with bridge monitoring.
Christoph Klauser, what is the service life expectancy of a bridge?
The service life is generally about 80 to 100 years. Many of the bridges we have in Europe today were built after the Second World War and are thus gradually nearing the end of their service lives.
What is the greatest challenge facing bridges?
Thomas Wuhrmann: Just like other structures, bridges are subject to a variety of influencing factors that can lead to wear and structural changes over time. Continually growing traffic volumes are, without a doubt, one of the greatest challenges. Bridges today suffer increased stress within short periods of time due to the volume of traffic and, most importantly, heavy vehicles using them. Many of today’s bridges were simply not designed for this enormous load when they were constructed. Added to this are environmental factors, such as wind and temperature, that a bridge is also exposed to over time.
A multitude of factors indeed, so how exactly are bridges monitored?
Christoph Klauser: Bridges are civil engineering structures, and these are governed by standards that define the inspections and checks the structures must undergo at particular intervals. Highway operators, such as ASTRA in Switzerland or Autobahn GmbH in Germany, are responsible for implementing these and commission specialized engineering consultants with the realization. Manual inspections and checks determine what condition the bridge is in. However, reliable data is needed to calculate the effective condition of and strain on a bridge with the models employed.
Data that Kistler, as an expert in measurement technology, is capable of recording?
Christoph Klauser: Yes, our products can make a significant contribution during both condition monitoring and active control of traffic volumes. And, while we are on the issue of traffic volumes, our Weigh In Motion systems can record traffic data with great precision. This means that all vehicles approaching or crossing the bridge are checked. In addition to the weight of the vehicles, information on the transit time and the vehicle type, length or speed can also be recorded in this manner. Recording the actual traffic load also helps in the subsequent step when it comes to reliably calculating the remaining service life expectancy of a bridge, rather than only using load assumptions based on a standard
And what about the actual condition of the bridge itself?
Thomas Wuhrmann: In addition to the volume of traffic, our measurement technology can also monitor the structural condition of the bridge itself (Structural Health Monitoring). This can, for example, be achieved with a combination of accelerometers and other systems that record the impact of traffic, the wind or temperature fluctuations continuously and synchronously. Consequently, signs of wear and aging processes due to traffic loads and the effects of weather are registered immediately.
But, as is often the case, more data does not automatically mean a better overview. Appropriate analytical options are needed if raw data is to be comprehensible for the end user and effective conclusions can be drawn from it. As a holistic solution provider, we can also provide the appropriate technology here. Our networked systems mean that the data collected can be displayed conveniently in a cloud-based Digital Hub. In addition to analyzing the high-precision measurement data collected with application-specific digital services, it is also possible to ascertain whether all the measuring systems used are perfectly coordinated with each other. The quality of the data is also assured at all times. Ultimately, a complete digital ecosystem is then created for monitoring the bridge.
What happens if a bridge is already in a critical condition?
Christoph Klauser: If it is already apparent that a bridge exhibits certain defects, it is even more important to ensure it is looked after and to monitor it appropriately. The service life of a bridge in this condition can often be extended considerably when the correct measures are taken. An example of such a measure is the restriction of use. This involves prohibiting vehicles that exceed a particular maximum weight (e.g. 20 tones) from crossing. Using our Weigh in Motion systems, the weight of all vehicles is registered in real time for this purpose prior to crossing the bridge. Any vehicle that is too heavy can automatically be diverted or prevented from crossing with a red traffic light.
Whereabouts around the world are bridges equipped with Kistler measurement technology?
Thomas Wuhrmann: Our sensors and measuring systems are in use on bridges all over the world. An example would be the El Carrizo highway bridge in Mexico. With a central tower that is 226 meters tall, El Carrizo is currently the second highest bridge in North America. The extremely busy route from the coast to the interior is mainly used by commercial vehicles. Following closure of the bridge for several weeks after a severe accident, two checkpoints with Weigh In Motion technology are today in operation, assisting the automated detection of overloaded vehicles.