Potential of the Deformation Area Difference (DAD)-Method for Condition Assessment of Bridge Structures

The construction industry ranks in the back rows in terms of digitalization. The numerous existing bridge structures require considerable effort for inspection and reliable assessment of their condition. However, the state-of-the-art for inspecting these structures still relies on the visual inspection realized by bridge inspectors. The current paper summarizes several research projects in the field of condition assessment of bridge structures at the University of Luxembourg by analysing the structural response due to dynamic excitation and static loading tests.
The latest development aims at using the most modern measurement techniques by combining them to a new method, the Deformation Area Difference (DAD)-Method in order to simplify and automatize at most the inspection process. The proposed DAD-Method is based on conventional static load deflection tests. It allows the localization of stiffness-reducing damage by using a very precise measurement of the deflection line and by combining this outcome to the deflection line generated by a simplified finite element model of the bridge. In order to investigate the condition of a bridge by the DAD-Method modern measurement techniques such as photogrammetry and laser scanning are used. In the framework of the conducted research, these techniques are also compared to traditional measurement systems such as total station and inductive displacement sensors as well as to digital levelling sensors. By theoretical examples and experimental tests, it can be shown that the DAD-Method is able to detect and localize damage when the damage level is dominant on the measurement noise.
This paper investigates also the application of the method on a real bridge structure in Luxembourg. All of the above-mentioned measurement techniques were used, whereby the photogrammetry is applied using both, stable tripods and an autonomous flying drone. This allows examining the accuracy of the different measurement systems when applied on a real-size structure.