Dynamic characterization of flexible structures through vision-based vibration measurements

Structural vibration is nowadays a crucial point for both potential safety and comfort problems due to larger structural vibrations. The problem of structural monitoring is therefore increasingly relevant also requiring vibration measurements to both estimate structural dynamic parameters and eventually predict potential damage or even failures. The problem is particularly crucial for very large structures, where the use of classic techniques (such as accelerometer-based measurements and strain estimation using either electric or optical-fiber strain gauges) presents some limitations due for example to access difficulties, for transducers installation. Moreover the load effect due to the transducers mass can become a major concern in the case of extremely slender structure, such as power transmission lines and in all the applications that involving long cables. In these latter cases contactless measuring techniques would be highly preferred, in order to avoid the mentioned load effects and ease of installation and, above all, to measure vibrations in many points at the same time with a single transducer (a camera). An image-based vibration measurement technique is proposed and qualified in this paper and an application to overhead transmission lines is shown as an example.