Concrete with a very high number of load cycles—Identification of stress levels for efficient investigation of fatigue behavior

Fatigue stresses are receiving increasing attention in structural engineering, particularly in the design of increasingly slender structures. However, the mechanical response of concrete—particularly its fatigue behavior under very high numbers of load cycles—is still scarcely understood. Conventional fatigue testing is extremely time-consuming, whereas increasing the loading frequency may lead to specimen overheating. Additionally, dynamic or inertia effects are to be considered concerning high frequency testing. This paper proposes a conceptual approach to determine cyclic stress levels causing fatigue failure in the very high cycle fatigue (VHCF). A test frequency of approximately 85 Hz, applied using a high-frequency pulsator with oscillating adapters, was found to be suitable for concrete cylindrical specimens with a diameter-to-height-ratio of 30 mm/90 mm. Potential dynamic effects of the test equipment were taken into account during result evaluation, thereby validating the proposed test method. Furthermore, the temperature increase of the specimens during testing was recorded, and its influence on the reduction of concrete compressive strength was considered. ... mehrThe study confirms that fatigue testing at approximately 85 Hz, when appropriately corrected for temperature effects as well as dynamic influences, provides reliable fatigue data comparable to those obtained from conventional low-frequency tests.