Experts from CTU UCEEB monitor the mechanic stress of a bridge using special sensors
Recent tragedy in Genoa in northern Italy that had been caused by a collapse of a highway bridge has led to many questions concerning the security of Czech bridges. Consequently, their ordinary inspections and regular monitoring of the load-bearing structures as well as their timely repairs are becoming more important. Experts from the Laboratory of Fiber Optics at CTU UCEEB who are testing sensors for measuring the mechanic stress which are built directly in the structure of the bridge over Moravská Dyje at present are also looking into these problems.
Bridges are considered to be the most important and most complicated structures within the road transport network which is constantly undergoing further development that reflects especially the increasing intensity of traffic. Bridge structures are totally exposed to the effects of environmental influences; therefore, it is important to know their present technical state. Regular surveillance of the actual mechanic stress of the load-bearing structure helps achieve this.
According to the Directorate of Roads and Highways of the Czech Republic, there are about 270 road bridges on first-class roads that are in a bad state; six of them are even in a structurally unsound state. These structures are either waiting to be reconstructed, or they are being reconstructed, or they will undergo a demolition and they will be replaced with new bridges. The structure which the measuring by CTU UCEEB in cooperation with the Safibra, s.r.o. company takes place on is a replacement of the original stone bridge over Moravská Dyje on the second-class road near the municipality of Staré Hobzí in the South Bohemian Region.
The monitoring of a bridge structure is carried out using glass-fiber FBG sensors which are integrated directly in the load-bearing bridge elements made of reinforced concrete. Thanks to that, it was possible to monitor the behavior of the structure as early as during the construction (maturing of the concrete, pre-tensioning of the load-bearing structure). After finishing the construction and putting the bridge into operation, experts from the Laboratory of Fiber Optics have been monitoring not only the mechanic stress of critical cross-sections, but also (among others) the intensity of traffic or the deformation of the structure due to changes of temperature.
The technology tested can ensure long-term continuous measuring of the bridge structure and it is also applicable in a dangerous environment due to its resistance to electromagnetic phenomena. Installing the sensors in the new bridge structure as early as during its construction can help easier evaluation of its technical state, revealing possible structure faults, or diagnosing the amount of degradation of each element in future. The system also allows monitoring the amount of load of the bridge during its lifetime and it can generate warnings before possible overloading occurs when the intensity of traffic increases significantly.