Drive-by Structural Monitoring using GNSS measurements at alpine bridges

Most bridges in Europe were built in the 1960s and 1970s and are now reaching the end of their design life. It is therefore important to monitor these bridges to ensure a safe operation for many years to come. Load tests are a common way of checking the health of an infrastructure. Such a test was carried out on a ~560m long motorway bridge (7 spans) in Austria. Previous studies have shown that geodetic GNSS (Global Navigation Satellite System) receivers with a data rate of 20Hz can be used for vibration monitoring. Therefore, for the load test, geodetic GNSS receivers were mounted on the moving load (2 trucks of 50 tons each) to test the capability of
drive-by GNSS measurements for structural monitoring of bridges. Additional
sensors (accelerometers, fibre optic cables) and prisms were mounted on span 6 and
7 and data was collected during the load tests. The frequency analysis performed with
the GNSS measurements agrees well with the frequency analysis performed with the
data from the other sensors, where the main frequencies occurred between 2-3Hz with amplitudes in the millimetre range. The advantage of drive-by GNSS measurements is the acquisition of data from the entire bridge. Therefore, the shape of the bridge (slack span of each span) and the dynamic behaviour (frequency response, mode shapes) can be derived from the same data at the same time.