MONITORING OF LOAD BEARING STRUCTURES WITH OPTICAL FIBER SENSORS

This paper shows how optical fibre sensors can be used to monitor load-bearing concrete structures. An optical fibre strain sensor is fitted with an internal thin spiral wire, and displays changes in attenuation as a function of the strain produced. Localised faults should be identifiable, because loads on concrete structures do not occur evenly. There are two measuring principles for integral monitoring, in which either one end or both ends of the sensor are accessible. Optical fibre strain sensors, which are directly embedded in the concrete, can provide information at any time, for example on the appearance and changes of emerging cracks in the monitored structural element. Here, specially designed sensors are placed in the concrete at positions known from static principles to be subject to heavy loads. Optical fibre sensors, integrated into the fibre bars of prestressing tendons made of composite fibre materials, provide information about the behaviour and functioning of the tendons. Extensive experiments were performed to check that the sensors met their specific requirements. Measurements with optical fibre sensors at the Ulenbergstrasse Bridge, Duesseldorf, Germany, for nearly three years, showed no observable change in the bridge structure. For the covering abstract of the conference see IRRD 858334. The French title of this paper is:- Surveillance des constructions a l'aide de capteurs a fibres optiques. The German title of this paper is:- Bauwerksueberwachung mit Lichtwellenleitersensoren.