Bridge Monitoring Using Geophones: Test and Comparison with Interferometric Radar

More than 30% of European highway bridges present structural criticalities. Their continuous health monitoring is a priority. Conventional sensors are accurate and reliable, but they are often too expensive for continuous monitoring. Possible low-cost alternative equipment are the geophones, that are able to detect the displacement of structures by integrating in time their response. They can be easily installed and can provide continuous health monitoring by transmitting the data to a remote server. The aim of this paper is to assess the capability of a geophone sensor to provide continuous, accurate and reliable data about the dynamic loads of a bridge. In order to validate its performance, it has been experimentally compared with an interferometric radar. As preliminary test the geophone has been fixed to a horizontal steel plate. The radar has been positioned under the steel plate in order to detect the same displacement component. The steel plate has been excited with controlled pulses. Finally a network of geophone sensors, provided with its control and transmission electronics, has been installed on a well-known bridge in Florence, Italy (the “Amerigo Vespucci” bridge). The interferometric radar has been installed under the deck close to an abutment. The obtained results both in controlled environment and in the in-field test are in good agreement, although the geophone appears less sensible to impulsive stimulus than the radar.