Investigation of displacements of road bridges under test loads using radar interferometry - Case study

Bridges, before putting into use, are subjected to test loads in order to their acceptance. According to Polish Standards, the aim of loads is to verify the computational model designed for the construction and to confirm the safety margins. Such tests are designed and executed under static and dynamic loads. In the case of static loads conventional surveying techniques are widely applied, while for dynamic loads the measurements using accelerometers are typically provided. These methods are characterized by significant limitations which include i.a. low sampling rate (measurements performed by total stations, digital levels, GPS receivers) and discrete (limited to points) nature of measurement (a set of accelerometers). The authors present the results of comparing the measurements carried out during test loads of a cable-stayed bridge, performed using classical measurement methods and ground-based radar interferometer. This innovative measuring device operates on the basis of stepped-frequency continuous wave modulation and microwave interferometry technique. It allows to determine deformation and vibration frequency of the object through a non-invasive observation of its behaviour at a frequency of up to 200 Hz.