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.
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.
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.
The fatigue behavior of plain concrete has been studied for decades, usually under compressive or tensile loading. Shear loading (mode II) has been almost completely neglected in the past. In contrast to cylindrical compression tests, this type of loading offers the advantage of precise load determination and a small, well-defined fracture surface. This paper presents a comprehensive experimental campaign of 66 shear tests, which was conducted to systematically investigate the monotonic, cyclic, and fatigue response of high-strength concrete under mode II loading. Since the material behavior under shear stress is strongly dependent on the concurrent lateral compressive stress, a new test setup was developed which allows simultaneous control of compressive and shear loading. One potential utilization for these shear fatigue tests is the validation of a promising hypothesis that suggests that the development of fatigue damage in concrete at subcritical load levels is governed by a cumulative measure of shear sliding. The qualitative influence of the lateral compressive loading on the displacement and damage development, fracture behavior, and fatigue life is analyzed and discussed. The test results indicate that there is no influence of the lateral compressive load level on the shear fatigue life, as long as the increase in shear strength is considered. Furthermore, concrete under mode II loading seems to have a longer fatigue life than concrete in standard cylindrical specimens under compressive loading.
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