Influence of loading speed and frequency on fatigue resistance
Table of contents
Project data
| Titel | Title Einfluss der Beanspruchungsgeschwindigkeit und der Belastungsfrequenz auf den Ermüdungswiderstand von Beton (EBBE-Beton) | Influence of loading velocity and loading frequency on the fatigue resistance of concrete (EBBE-Beton) Förderer | Funding Deutsche Forschungsgemeinschaft (DFG) Zeitraum | Period 08/2020 – 07/2023 Projektleiter | Project manager Prof. Dr.-Ing. Steffen Marx Bearbeiter | Contributor Raúl Enrique Beltrán Gutiérrez, M. Sc. |
Report from the year book 2021
Fast or slow to concrete fatigue?
Concrete specimen under cyclic loading
Concrete bridges are subjected to a large number of loading cycles caused by cars, trucks or trains during their service life. As a result, the concrete fatigues at the areas subjected to high stresses. In recent years, knowledge gaps, as well as discrepancies between the fatigue behaviour observed in the laboratory and the actual fatigue behaviour of concrete structures, have been discovered. For example, fatigue strengths calculated based on laboratory tests have a lower value than the actual fatigue strengths estimated in the real structures. The high cyclic loading frequency and the resulting internal temperature increase during the laboratory tests apparently cause additional damage to the concrete specimens.
Currently, concrete specimens are tested under laboratory conditions in fatigue tests at the highest possible cyclic loading rate until fatigue is reached. This is done to minimize cost and testing time. For example, to simulate the number of cyclic loads on a specimen that a bridge will be subjected to over 10 years, it would take about 23 days under normal laboratory conditions with a loading frequency of fp = 5 Hz. Moreover, one would need several many specimens to validate the results of the tests. Therefore, it seems logical to increase the cyclic loading rate. Only if the testing times for the fatigue tests could be shortened without compromising the quality of the results, it will be possible to realistically simulate the fatigue damage evolution over the expected lifetime of the bridge in the laboratory.
As part of this research project, numerous tests will be conducted at different cyclic loading rates and temperature conditions to relate the fatigue strength of concrete to the above factors. The experimental data will later be used to develop models that take into account the influence of the loading rate as well as the temperature increase on the development of fatigue damage. With the help of the models developed in this research project, the previously insufficient applicability of laboratory results from fatigue tests to real component situations will be made possible.