To detect damage in bridge infrastructure in first stages is one of the most challenge goal to manage the maintanance of these structures. For this reason, many methods have been proposed so far. One of the most promising methods are those based on vibration monitoring. It is well done that modal parameters of structures, namely, frequencies, damping ratios and mode shapes, change with structural damage. However, this change is many times too small for been detected directly. To handle that, mathematical methods capable of detecting small changes in the modal parameters have been proposed. Not all these methods can be applied to bridge structures and only a small group of them have been successfully applied in some circunstances.