precision limits of lifetime prognoses - experimental and numerical investigation of an existent bridge structure subjected to fatigue

• Applicant: Dr.-Ing. Mark Alexander Ahrens
• Subject Area: Structural Engineering, Building Informatics and Construction Operation
• Term: since 2012
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 221282822

A sound condition prognosis of infrastructure buildings, in particular bridges, and their assessment combined with a rational decision on the implementation and planning of responsible maintenance and replacement measures is still the main focus of many engineers in practice. In addition to the federal motorways and the German railways tracks, the focus is now increasingly shifted towards structures in municipal responsibility. What all cases have in common is that actions are usually taken when damage has occurred and restrictions in use are threatening with their enormous macroeconomic consequences. Then reasons are sought, measurements are performed, concepts are planned and countermeasures are coordinated and finally taken. This position appears unnecessarily passive and should be changed into a proactive one in the future. Necessary tools are provided through this project. Based on the findings and further developments of the preliminary proposals in the fields of fatigue, temperature control and service life prediction, the knowledge gained so far is now to be used consistently in order to enable not only to precisely assess the fatigue service life of bridges in the future by means of targeted and monitored measures, but even to actively extend it. By means of active temperature induction with adapted technologies, engineers can no longer just passively observe stress amplitudes presumably increased by temperature (e.g. by monitoring), but can actively induce stresses into structures and control them for the benefit of the public. The conceptual lifetime indicator enables decision makers to check the success of such measures if necessary and to quantify lifetime gains. This provides a tool to support well-founded decisions on the maintenance of our infrastructure already at an early stage. In this project, for the first time a real large-span bridge, the "Hochstraße am Nordfriedhof" provided by our cooperation partner, the state capital Düsseldorf, is to be equipped in such a way as to prove its practical feasibility and to gain a first reference case. To do this in an optimal way with high quality results, final laboratory tests are scheduled beforehand. Potential influencing factors of the fatigue life of single wires clamped on both ends as an essential component of the fatigue life indicator (force induction, frequency, notch generation) will be clarified and quantified separately via individual Wöhler curves according to the interactive method. The temperature induction and control is tested under real conditions in a model (scale 1:2) and optimally adjusted to the requirements on site. Installation and operation over several months proves its effectiveness, which is demonstrated by measuring and recording the temperature-reduced stress amplitudes under real traffic in comparison to the original Wöhler curves of the tendons.

• DFG Programme: Research Grants