Fiber reinforced concretes (FRC) proved to be a promising solution to address fatigue design in relevant fields of application including infrastructures such as bridges, pavements, infrastructures for energy harvesting which are often exposed to cyclic loading during their service life. The objective of this session is to share the advancements in FRC fatigue testing, characterization, and modeling, and report successful case studies implemented in the field.
Learning Objectives:
(1) Fatigue Behavior of Steel Fiber Reinforced Concrete Pavements;
(2) Predictive models for fatigue life of Fiber Reinforced Concrete;
(3) Damage mechanisms in fiber-reinforced concrete subjected to flexural fatigue;
(4) The effect of high-cycle fatigue on a high-performance fiber-reinforced concrete (HPFRC) with hybrid fiber reinforcement.
Flexural Fatigue Response of SFRC Elements: Crack Width and Residual Strength Performance
Presented By: Albert Antequera
Affiliation: University of Politecnica De Catalunya
Description: This research is focused on the mechanical behavior of steel fiber reinforced concrete (SFRC) under cyclic loading, focusing on fatigue tests conducted on pre-cracked specimens. These tests, conducted under three-point bending configuration, considered initial crack widths and load levels typical of service limit states. The rate of crack increment showed a strong correlation with the number of cycles to failure, while damage evolution correlated with stiffness reduction. The hysteresis loop area was used to assess energy dissipation and damage accumulation, with higher loads leading to faster failure due to increased energy dissipation. Visual analysis of SFRC cross-sections indicated fatigue failure resulted from fiber pull-out, fiber-matrix damage, and fiber rupture. An improved model for crack evolution under cyclic loading was developed. Three probabilistic methods for predicting SFRC fatigue life demonstrated similar accuracy.
Fatigue Characterization of a High-Performance Steel Fiber Reinforced Concrete (HPFRC) by Means of Compressive and Flexural Tests
Presented By: Liberato Ferrara
Affiliation: Polytechnic University of Milan
Description: The use of fiber-reinforced concretes (FRC) for infrastructures subject to fatigue loading can result into an extension of their service life by providing enhanced ductility and toughness. The cyclic actions might affect the fiber-matrix interface and it is necessary to assess to what extent the degradation hinders the mechanical properties of these materials. Currently, the only predictive models for fatigue life and performance reduction are empirical. Therefore, a mechanical characterization is required for any mix whose composition and performance might differ from the one pertinent to the database the models are based on. This work presents the effect of high-cycle fatigue on a high-performance fiber-reinforced concrete (HPFRC) with hybrid fiber reinforcement. The material was characterized under compressive and flexural loads at various stress ranges. The Palmgren-Miner rule was applied to predict the fatigue life of the material. The results showed the effects of fatigue loading on the strength of the material. The compressive strength remained constant in most cases, while the flexural performances were slightly reduced by the cycling process. The predictive capacity of the P-M model proved to be reliable only in limited scenarios.
Damage Mechanisms in Fiber-Reinforced Concrete Subjected to Flexural Fatigue through the Analysis of Cyclic Creep Curves
Presented By: Miguel Vicente
Affiliation: Universidad De Burgos
Description: The fatigue response of fiber-reinforced concrete (FRC) can be characterized through the number of load cycles to failure. However, this parameter does not provide any information on the degradation process that the material undergoes during its fatigue life. For this purpose, it is more interesting to study cyclic creep curves, which relate the maximum strain as a function of the number of cycles. In the case of flexural fatigue, these curves represent the maximum crack opening (CMOD) versus the number of cycles.
While in compressive fatigue the cyclic creep curves in FRC have a characteristic S-shape, in flexural fatigue this is not always the case. Several works indicate that, under certain fiber contents and stress levels, a double fatigue mechanism (a double S-curve) is observed. First, a damage process in which the concrete does not show macro-cracks, which is governed by the matrix (matrix fatigue). And then, once the concrete has cracked, another much more ductile damage process, dominated by the connection between fibers and matrix (fiber-matrix bond fatigue).
In this work, this double fatigue mechanism appearing in FRC fatigue is studied. For this purpose, 75×75×300 mm prismatic specimens with three different fiber contents (0.3%, 0.6% and 1%) were fabricated. The specimens were subjected to flexural fatigue under the same relative stress levels. The results reveal that the probability of this dual behavior is higher the lower the fiber content. In addition, it is observed that fiber-matrix bond fatigue, being a faster damage process, has more impact on fatigue life. In this sense, a good correlation is found between the slope of the secondary branch of the cyclic creep curves and the fatigue life.
Modeling of Mechanical Degradation of Steel Fiber Reinforced Concrete under Flexural Fatigue Loading
Presented By: Barzin Mobasher
Affiliation: Arizona State University
Description: - An approach is proposed to model the damage due to mechanical degradation in FRC materials using a state variable that is a function of fatigue loading parameters. Experimental tests are conducted to characterize the fatigure response of FRC flexural beams under closed loop tests after the sections have been subjected to pre-cracking. The complete composite quasi-static mechanical response is characterized to obtain the envelop curve. The rate of CMOD increase under fatigue loading is also measured and calibrated using a power law equation as well as the S-N curve.
Using the backcalcuation model constitutive relations for tension and compression consisting of a quad-linear model for tension, and elastic perfectly plastic model for compression are used to obtain the moment-curvature response. Crack opening is subsequently verified using the characteristic length and the tensile strains measured allow for the evaluation of crack extension and CMOD increase under fatigue. The methodology was applied for three distinct concrete compositions and the results are used to replicate the experimental results for the CMOD evolution due to the cyclic fatigue.
Fatigue Loading on SFRC Reinforced Floors: From Research to Analytical Models
Presented By: Hendrik Thooft
Affiliation: Bekaert
Description: The presentation presents the findings of a comprehensive research program conducted by Bekaert over the past year, aimed at evaluating the performance of Steel Fiber Reinforced Concrete (SFRC) in the application of industrial floors, pavements and concrete roads. The study involved extensive fatigue testing, which is traditionally time-consuming and yields highly scattered results. Despite these challenges, a large database was compiled to develop a reliable analytical model.
The research was conducted in collaboration with several universities and at the Bekaert Concrete Expertise Centre. The studies that form the basis for our analytical model include:
- “Fatigue Fracture of Fibre Reinforced Concrete in Flexure” from IIT Madras, India,
- “Fatigue Behaviour of Steel Fibre Reinforced Concrete Pavements” from the University of South Wales,Sydney, Australia, an internal test report from Wu Han University of Technology, China, and
- “Modellbildung und numerische Analysen zur Ermüdung von Stahlfaserbeton” from Ruhr University Bochum, Germany.
The paper will highlight the key takeaways from these different research programs. Based on the test results, an analytical model was derived that enables designers to calculate the Serviceability Limit State (SLS) for fatigue loads. This research represents a significant advancement in the understanding and application of SFRC in industrial flooring.