Condition assessment of bridge structures by damage localisation based on the DAD-method and close-range UAV photogrammetry

The provided dissertation presents a so-called “Deformation Area Difference (DAD)” method
for condition assessment of existing bridges, especially for the detection of stiffness-reducing
damages. The method is based on the one hand on conventional static load deflection
experiments and on the other hand on a high-precision measurement of the structural deflection.
The experimental load on the bridge should be generated within the serviceability limit state in
order to enable a non-destructive inspection.

In the course of the laboratory tests, the most innovative measuring techniques were applied,
whereby the photogrammetry has delivered promising results. With the help of additional
studies on the influences of camera quality and calibration, the measuring precision of
photogrammetry could be brought to its limits.

Both the theoretical investigations and the laboratory tests showed the successful use of the
DAD method for the identification of local damages. Therefore, the first in-situ experiment was
carried out on a single-span, prestressed bridge in Luxembourg. The knowledge gained from
this was combined with statistical investigations based on finite element calculations and
artificially generated measurement noise effect in order to determine the application limits, such
as the achievable measurement precision, identifiable degree of damage, required number of
measurement repetitions, influence of the damage position, optimal size of the structural
deformation, etc.

The development of the DAD method ready for application usefully supplements the state of
the art and contributes to the reliable assessment of the bridge condition.