Bridge Monitoring by a Monostatic/Bistatic Interferometric Radar Able to Retrieve the Dynamic 3D Displacement Vector

A monostatic/bistatic radar for retrieving the three-dimensional (3D) displacement vector is proposed for static and dynamic monitoring of bridges. The radar is particularly suitable for dynamic test, as it is able to detect the three components at high sampling frequency (132 Hz, in the reported case study). The monostatic/bistatic technique makes use of a multiple input multiple output (MIMO) interferometric radar equipped with two transponders. Each single transponder consists of an antenna and an amplifier and it is connected to the radar with a radiofrequency (RF) cable. A simulation has preliminarily estimated the expected accuracy in terms of positing error of transponders. The equipment and the method were experimentally tested in a controlled scenario using a vertical steel bar as target. Finally, the method was applied on a real case of interest: the dynamic monitoring of a bridge (“Ponte Nuovo sull’Arno” in Lastra a Signa, Firenze, Italy) excited by the vehicular traffic. The 3D displacement vector was detected in time and the modal frequencies of each component were estimated.