How does a bridge behave under targeted and controlled loading? Answers to this question are provided by measurements aimed at visualizing how a structure actually moves in response to different loads. One recent example is the Budapester Strasse bridge in Dresden. A loading test was carried out in August 2026 to investigate how the damaged structure responded to defined loading. This analysis was carried out using various measuring procedures and with support from Fraunhofer IIS in Dresden, which provided high-precision, non-contact deflection measurements.

© Fraunhofer IIS
© Fraunhofer IIS

These measurements were taken using radar sensors of the kind originally developed for applications in the automotive sector. By means of phase-based interferometric analysis, such measurements can be used to derive precise information about how a structure moves. Non-contacting sensors record relative displacements along their line of sight and can measure not only deformations but also vibrations. This allows measurements to be taken down to the millimeter or even sub-millimeter scale.

It is possible, for example, to record the extent to which a bridge section bends under a defined load. The measurement data serve as an additional basis for evaluating how a structure actually behaves. In the case of the Budapester Strasse bridge, these data were evaluated in conjunction with further measurements and analyses.

From individual measurements to continuous structural monitoring

This line of research is about more than just individual load tests. Indeed, if deformation and vibrations are recorded over a prolonged period of time, it is possible to identify changes in a structure’s behavior.

The radar does not detect damage such as cracks or corrosion directly. Rather, it measures their possible effects on the mechanical behavior of a structure. Therefore, the data need to be combined with further information and evaluated by experts.

Research is underway into this topic at Fraunhofer IIS. The research project RICARES revolves around the further development of radar-based sensor systems for continuous structural monitoring of bridge and rail infrastructure. Among other things, this research uses economical radar sensors from the automotive sector and a setup that requires the least possible installation and maintenance work. The aim is to allow multiple measuring nodes to be connected and structures to be observed over a longer period of time.

The measurements at Budapester Strasse demonstrate what radar-based sensor technology can already contribute to the inspection of structures. Networked measuring systems could potentially provide additional information about how bridges and other structures change during operation. This would provide additional data between regular structural inspections, allowing changes in the structure’s behavior to be detected at an early stage and better interpreted.