This contribution aims to analyze the deterioration behaviour of steel fibre-reinforced high-performance concrete (HPC) in both experiments as well as numerical simulations. For this purpose, flexural tensile tests are carried out on beams with different fibre contents and suitable damage indicators are established to describe and calibrate the damage behaviour numerically using a phase-field model approach. In addition to conventional measurement methods, the tests are equipped with acoustic emission sensors in order to obtain a more precise picture of crack evolution by observing acoustic events. It is shown that, in addition to classical damage indicators, such as stiffness degradation and absorbed energy, various acoustic indicators, such as the acoustic energy of individual crack events, can also provide information about the damage progress. For the efficient numerical analysis of the overall material behaviour of fibre-reinforced HPC, a phenomenological material model is developed. The data obtained in the experiments are used to calibrate and validate the numerical model for the simulation of three-point bending beam tests. To verify the efficiency of the presented numerical model, the numerical results are compared with the experimental data, e.g., load-CMOD curves and the degradation of residual stiffness.

This contribution aims to describe and model the fatigue behaviour of steel fibre-reinforced concretes under bending loading by combining experimental and numerical approaches on different scales. Initially, single fibre pull-out tests were conducted with different fibre types and inclinations, both with and without hooked-ends. Based on the results, an ellipsoidal unit cell is constructed to simulate the material behaviour in preferred fibre orientation. Then, low- and high-cycle bending tests on notched beams with varying fibre contents and compressive strengths were performed. It is shown that the deterioration development in these tests progresses similarly regarding load-levels and loading history. However, significant differences in deterioration development occurred between the compressive strengths and fibre contents tested. A phenomenological material model for the beam tests is constructed which is not only capable to predict the load to crack-mouth-opening behaviour for different steel fibre contents, but also the deterioration in terms of residual stiffness for low-cycle tests. Finally, the results suggest the conclusion that deformation controlled low-cycle tests are a suitable means to estimate high-cycle fatigue behaviour. Furthermore, constant deterioration development in the second phase of damage provides a suitable basis for estimations of failure and can be applied in numerical cycle-jump approaches.

This study characterizes the sequential flexural fatigue behavior of fiber-reinforced concrete (FRC), in which two damage mechanisms occur in sequence: (i) matrix fatigue up to cracking, followed by (ii) fiber-matrix bond fatigue. A simple criterion is proposed that, based on the relationship between static strengths (fLOP and fR) and the maximum cyclic stress level (σfat,max), allows anticipation of this sequential behavior. When σfat,max is below both fLOP and fR, the cyclic creep curves (defined as the maximum CMOD per cycle versus the number of cycles) display two concatenated inverted-S segments, reflecting the two damage processes.The method is validated through an experimental program on three FRCs with fiber contents of 0.3%, 0.6%, and 1.0%, subjected to flexural fatigue under constant stress levels. The results confirm that the proposed criterion correctly discriminates between the general case and particular cases in which only one of the two mechanisms operates.In addition, the Sparks–Menzies relation between the slope of the central segment of the cyclic creep curve (dCMOD/dn) and the fatigue life (N) is extended to derive closed-form expressions that estimate, with high accuracy, the number of cycles to matrix fracture (Nm) and the remaining cycles to final failure (Nf–m). This tool provides a practical basis for assessing accumulated damage and optimizing the design and maintenance of FRC structural elements subjected to cyclic loading.