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Test & measurement


Bridge monitoring solutions create safety


Infrastructures are continuously ageing – and at the same time, traffic volumes are soaring. This creates a hazardous situation, but the right technologies can at least reduce the risk. On the one hand, vibration measurements supply valuable data about the exact condition of a bridge; and on the other, Weigh In Motion (WIM) systems make it possible to collect comprehensive usage data and restrict access as appropriate, as Kistler explains


T


he Morandi Bridge near Genoa, Italy collapsed in summer 2018. The four- lane viaduct was part of the A10


autostrada, an arterial route that carries heavy traffic. This accident in the heart of Europe claimed 43 lives and even today, its causes have not been clarified beyond doubt. Was a design error to blame? Was inadequate maintenance responsible? And, above all: could the accident have been prevented – and if so, how? We shall have to wait for the official investigative report by the Italian authorities to provide reliable answers to these questions. The fact is that road bridges involve enormously complex and interrelated


infrastructure problems. The Genoa accident is merely the tip of the iceberg: many other bridges collapse without claiming victims, or without attracting public attention. In the US alone, for example, there are 578,000 highway bridges: most of them were built shor tly after the Second World War, and they have an average lifespan of about 70 years. The situation is similar in Germany, where exper ts have been warning for decades that growing numbers of bridges are reaching their critical age, or are in need of restoration. How can these structures be monitored efficiently? How can their maintenance be properly targeted? And how can maximum safety be ensured for their users?


Bridges are in the process of ageing – so they need


accurate monitoring


WhaT Is The real cOndITIOn Of The brIdge? There are three different ways to tackle these issues. The first approach is to protect the bridge by preventing heavy vehicles from crossing it. The impact of a vehicle on the road infrastructure is related to the vehicle’s weight by a power of four, so this factor has an enormous influence on a bridge’s life expectancy. A second method is to measure the vehicles’ axle loads per unit of time: this approach provides information about the stress on the road paving and the structure as a whole.


24 And thirdly, changes to the bridge itself can


be monitored. Measurement systems based on accelerometers collect data about critical changes to the structure and “health” of the bridge: this method is known as structure health monitoring (SHM) or bridge health monitoring. By recording movements and vibrations, these systems permit conclusions about stress and possible corrosion of the structure. The Kistler Group offers tried-and- tested products that are suitable for all methods of bridge monitoring: products that help to preserve valuable infrastructure and make it safe. The following summary explains the technical basis and describes some examples of applications. Kistler accelerometers specifically designed


for bridge health monitoring are deployed on bridges worldwide to measure influences caused by traffic, wind, and temperature fluctuations. Measurement systems of this sor t are installed on the Great Belt Bridge across the Baltic Sea in Denmark, and in bridges over the Yangtze River in China and the Mississippi in the US. For example, 26 Kistler accelerometers are operating on the Interstate 35W in Minneapolis, Minnesota, built in 2009 to replace the collapsed bridge over the river. Twelve of these sensors measure vibrations in the centre of the concrete piers. Four teen more


April 2019 Instrumentation Monthly


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