GPS sensors can be used on bridges for structural health monitoring by measuring the movement and deformation of the bridge over time. The sensors can be placed on various locations on the bridge and can measure changes in position and orientation with high precision. This data can be used to monitor the structural integrity of the bridge, detect potential problems, and aid in maintenance and repair decisions. Additionally, GPS data can be used in conjunction with other sensor data, such as strain and temperature measurements, to provide a more complete picture of the bridge’s health.
But in order for GPS signals to be usable for high precision displacement in the cm range they need to be referenced to a base station at close proximity to the construction which is stable without movement. This approach is called RTK.
The basic principle of RTK is to use a fixed base station to measure the phase of the GPS signal and a mobile receiver to measure the same signal at a different location. The difference between the measurements at the two locations is then used to compute the precise relative position of the mobile receiver with respect to the base station.
To achieve this, RTK requires a radio or cellular link between the base station and the mobile receiver, which allows the base station to send its measurements to the mobile receiver in real-time. The mobile receiver then uses these measurements to correct its own GPS measurements, resulting in a much higher degree of precision. Typical RTK precision is 1-2 cm in the horizontal plane and 2-5 cm in the vertical plane.
On a suspension bridge the GPS sensors can be used for:
- Determining the vertical displacement on the deck from different loads such as vehicles, wind or construction equipment.
- Global displacement of the bridge to compare to design specifications.
- Clearance between the water and bridge deck (used in combination with a water radar).