The fatigue of concrete has been the subject of research for many years, and yet, there are still open questions. In particular, the fatigue‐induced damage evolution accompanied by a stress redistribution process propagating through the concrete structure is still not fully understood. So far, there are only few experimental studies addressing the fatigue propagation through a material zone occurring, for example, in beams with a pulsating, nonuniform stress profile. To investigate the influence of such stress configurations on the material and structural degradation process, a measuring concept has been developed combining digital image correlation, fiber optic sensors, and conventional strain gauges. The presented experiments visualize the propagating fatigue degradation in the compression zone of prestressed concrete beams subjected to fatigue loading. Based on the developed measurement concept, the quantitative foundation for a comprehensive validation of design rules and material models accounting for concrete fatigue can be significantly extended.

In civil engineering, the analysis and characterisation of structural phenomena is key for the deviation of mechanical models and strongly depends on experimental studies. For this reason, the development of new measurement techniques plays a crucial role in research to allow capturing the mechanical behaviour of structures. In this context, distributed fibre optic sensing (DFOS) gained attention during the last years. Advantageous properties such as minimal invasiveness and quasi-continuous strain measurement enable new possibilities in structural monitoring. DFOS is able to sense minimal strain variations, yet this often results in recording unwanted anomalies. Thus, to generate the best results from raw measurement data, it is crucial to use a robust and reliable post-processing procedure. In order to meet this requirement, the software solution FOS Evaluator was developed using the Python programming language, targeting the most important aspects that may occur when using DFOS. Those aspects comprise a high data volume, disturbances and anomalies in the measured data and the necessity to carry out calculations with acquired data sets. In this paper, functionality and background of FOS Evaluator are presented and discussed. Furthermore, several methods for post-processing and evaluating DFOS measurements are presented, consisting of multiple functions for reducing, cleaning, or smoothing strain data, and calculating various mechanical properties from filtered measurements. Finally, the functional scope of FOS Evaluator is illustrated by various application examples in structural concrete.

In research on concrete constructions, fiber optic sensor technology is becoming increasingly important. It enables high‐frequency and quasi‐continuous measurement of temperature and strain distribution. Furthermore, this technology offers the opportunity to determine the crack width within the cross section of specimens and not, as with conventional instrumentation, only from the outside. While experience for application of fiber sensors in steel‐reinforced concrete research already exists for several years, only few findings are available for textile‐reinforced concrete (TRC). This article gives a short overview of the principle of fiber optic sensor technology, presents possible concepts for utilization in TRC testing, and explains the necessary post‐processing steps for the preparation of the measurement results by means of an example from current research. Finally, the results are validated with conventional measuring methods and the applicability and further challenges are discussed.

An economically efficient yet safe design of concrete structures under high-cycle fatigue loading is a rather complex task. One of the main reasons is the insufficient understanding of the fatigue damage phenomenology of concrete. A promising hypothesis states that the evolution of fatigue damage in concrete at subcritical load levels is governed by a cumulative measure of shear sliding. To evaluate this hypothesis, an experimental program was developed which systematically investigates the fatigue behavior of high-strength concrete under mode II loading using newly adapted punch through shear tests (PTST). This paper presents the results of monotonic, cyclic, and fatigue shear tests and discusses the effect of shear-compression-interaction and load level with regard to displacement and damage evolution, fracture behavior, and fatigue life. Both, monotonic shear strength and fatigue life under mode II loading strongly depend on the concurrent confinement (compressive) stress in the ligament. However, it appears that the fatigue life is more sensitive to a variation of shear stress range than to a variation of compressive stress in the ligament.

Despite of intensive research on concrete fatigue, the transfer of fatigue characteristics determined at the material level to the structural level remains a challenging issue. In this paper, the propagation of fatigue‐induced damage through the concrete structure is analyzed using a microplane fatigue model for concrete recently developed by the authors. To this end, our recent experimental study in which the fatigue propagation was monitored at the structural level represented by prestressed concrete beams is used to derive a general interpretation of the stress redistribution process using of the developed model. The numerical studies show that the developed microplane fatigue model provides a powerful computational tool for in‐depth analysis of the correspondence between the fatigue behavior at the material and structural scales in a wide range of load configurations. In addition, the thermodynamically based constitutive model allows for the quantification of the energy dissipation during the process, revealing the possibility of deriving material‐specific energetic characteristics that can further help to make the predictions of fatigue life more accurate.