ABSTRACT
A concrete arch bridge in the city of Porto is equipped with a monitoring system continuously recording structural vibrations. The vibration characteristics are extracted from the measurements using automatic output-only identification. Statistical deviation of the natural frequencies of the structure can be used as an indication of damage. Since the variable environmental and operational conditions also affect these features, a minimum mean square error estimation algorithm was used to eliminate their influences from the data. The measurement of the environmental variables (e.g. temperature) is not necessary. During two years, no damage emerged, which is in agreement with the damage detection results. For damage simulation, a constant frequency shift, quantified by means of a numerical model, was added to a set of experimental samples. After the artificial introduction of damage, the extreme value statistics control charts showed an abrupt and permanent change in the data, from which damage could be detected.
