Dynamic Displacement Monitoring of Bridges Using Dual Monostatic Ground-Based MIMO Radar Interferometry

As bridges deteriorate over time, the need for effective bridge structural health monitoring (SHM) becomes increasingly critical. Dynamic displacement serves as a key indicator for identifying potential structural issues. This study presents a non-contact, marker-less, cost-effective, portable, and image-domain dynamic displacement estimation methodology using ground-based multiple-input multiple-output (GB-MIMO) radar interferometry for bridge SHM. A dual monostatic GB-MIMO radar configuration, combined with a practical photogrammetry-based geocoding approach was introduced to enable two-dimensional (2D) displacement vector estimation. The proposed framework was validated through controlled outdoor experiment as well as field deployment on a three-span steel box girder bridge, utilizing two off-the-shelf W-band MIMO radar units. Radar measurements captured vertical deflection responses induced by moving vehicle loads, with negligible horizontal displacement. Validation against a laser displacement meter (LDM) confirmed sub-millimeter displacement accuracy. Additionally, the extracted natural frequencies showed strong agreement with finite element method (FEM) based numerical analysis, demonstrating the system’s capability for accurate dynamic characterization of bridge structures.