Microwave Radar Interferometry as a Cost-Efficient Method of Monitoring the Structural Health of Bridges in New Zealand

The health monitoring of civil infrastructure is becoming more common for investigating actual structural behaviour, allowing early damage detection and helping to protect critical structures. In the New Zealand infrastructural context in particular, the introduction of high-productivity motor vehicles (HPMVs) along with the damage caused by recent earthquakes has resulted in a growing need for verification that bridges are performing as expected. The application of “classical” instruments such as accelerometers and linear variable differential transformers (LVDTs) are very expensive due to high installation costs and the need for a continuous power supply. However, radar interferometry is a promising alternative which can detect structural displacements without directly accessing the bridge, offering not only time and cost savings but also the capability to investigate structures where access is difficult or hazardous. This paper presents a health assessment of a bridge crossing the Rangitata River in New Zealand using this radar technology. Previous surveys of the bridge indicated that it was under capacity for supporting full HPMV loads. The structural performance was assessed by monitoring the maximum vertical mid-span displacements under live traffic conditions. The fundamental resonant frequencies were also measured to confirm the actual support conditions associated with the pier joints.