Search

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. Highlights: Structural experiments validate the constitutive fatigue hypothesis.Damage‐induced energy dissipation is an objective value for fatigue characterization.Insights into the fatigue life extension of concrete at the structural level are provided.Structural stress redistribution induces variable load amplitudes at local level. [ABSTRACT FROM AUTHOR]

The limited understanding of the fatigue behavior of reinforced and prestressed concrete members is one of the reasons why many structures do not reach their expected service life. Without a deeper theoretical understanding of the fatigue phenomena in the various fatigue process zones, reliable fatigue life predictions are not possible. This paper provides a classification of the major fatigue process zones and mechanisms in reinforced and prestressed concrete members, accompanied by a brief review of recent developments in design rules, experimental characterization, and modeling approaches specific to each fatigue process zone and mechanism. The limitations of current approaches to fatigue characterization and modeling are also discussed, highlighting the need for further research in this area. [ABSTRACT FROM AUTHOR]

The establishment of a simple engineering rule for predicting the fatigue failure of concrete has been pursued over the past decades. An energetic approach to the matter seems to be an attractive option that many researchers have embraced. In the present work, the authors attempt to contribute to the establishment of such a rule. In particular, the energy dissipation of confined concrete subjected to shear cyclic loading is studied and quantified. For this purpose, a microplane fatigue model recently introduced by the authors, referred to as MS1, is used. It aims to capture the fundamental inelastic mechanisms driving the tri‐axial stress redistribution within a material zone during the fatigue damage process in concrete. To this end, the fatigue damage evolution is linked to a measure of cumulative inelastic shear strain at the microplane level, reflecting the accumulation of fatigue damage due to internal shear/sliding between aggregates at subcritical pulsating load levels. To isolate the dissipative mechanism mentioned above, test configurations with dominant shear stress seem to be more appropriate. In the present work, a punch‐through shear test (PTST) FE model is used to induce shear‐dominated stresses and strains along the ligament of a specimen. Numerical studies are first presented to evaluate the behavior and energy dissipation at the elemental interface level. The interface is introduced in the MS1 microplane material model, which is capable of reproducing the concrete behavior under monotonic, cyclic, and fatigue loading with consistent set of material parameters. Quantification of the energy dissipation for each introduced dissipative mechanism is performed at each microplane and integrated via a well‐established homogenization scheme to evaluate the macroscopic energy dissipation. Later, an analysis of the energy dissipation of the PTST process zone is performed for cyclic loading under two different subcritical cyclic load amplitudes. [ABSTRACT FROM AUTHOR]

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. Highlights: Design of a test setup for the analysis of compressive fatigue propagation in concreteEvaluation of a coordinated monitoring concept combining various measurement techniquesVisualization of the propagating fatigue degradation of prestressed concrete beams [ABSTRACT FROM AUTHOR]

This paper aims to fill the gap in multi-axial fatigue characterization of concrete by presenting a comprehensive numerical analysis of data from the punch-through shear test (PTST), which allows control over combined shear and compression loads in the tested ligament. To accurately reproduce the degradation process in this multi-axial configuration, a material model must capture two key effects: (i) dissipative behavior at the inter-aggregate level during subcritical pulsating loading and (ii) fatigue-induced tri-axial stress redistribution in the test ligament. The recently published MS1 model by the authors effectively incorporates these features, thereby enabling a deeper interpretation of the experimental data. The former effect is seamlessly integrated into the model using the Lemaitre-type fatigue hypothesis, facilitating the direct derivation of general evolution equations. The latter effect is efficiently represented through the microplane homogenization framework. The model's predictions for PTST response under monotonic shear loading with varying levels of radial confinement align well with experimental results. Similarly, the simulated fatigue response accurately reproduces the experimentally observed S-N (Wöhler) curves. Further studies demonstrate the model's ability to predict the effect of fatigue loading sequence. A thermodynamically-based formulation provides an energetic interpretation of this effect, offering a quantitative breakdown of energy dissipation attributed to individual dissipative mechanisms over the lifetime of the material. The studies show that damage-induced dissipation remains almost constant regardless of different fatigue loading histories. • Experimental validation of constitutive fatigue hypothesis for multi-axial loading. • Visualized uniformity of fatigue degradation process over the lifetime. • Damage-induced energy remains almost constant for varied fatigue loading. • Prediction and energetically based explanation of the effect of loading sequence. [ABSTRACT FROM AUTHOR]

The phase field method has gathered significant attention in the past decade due to its versatile applications in engineering contexts, including fatigue crack propagation modeling. Particularly, the phase field cohesive zone method (PF-CZM) has emerged as a promising approach for modeling fracture behavior in quasi-brittle materials, such as concrete. The present contribution expands the applicability of the PF-CZM to include the modeling of fatigue-induced crack propagation. This study critically examines the validity of the extended PF-CZM approach by evaluating its performance across various fatigue behaviors, encompassing hysteretic behavior, S-N curves, fatigue creep curves, and the Paris law. The experimental investigations and validation span a diverse spectrum of loading scenarios, encompassing pre- and post-peak cyclic loading, as well as low- and high-cyclic fatigue loading. The validation process incorporates 2D and 3D boundary value problems, considering mode I and mixed-modes fatigue crack propagation. The results obtained from this study show a wide range of validity, underscoring the remarkable potential of the proposed PF-CZM approach to accurately capture the propagation of fatigue cracks in concrete-like materials. Furthermore, the paper outlines recommendations to improve the predictive capabilities of the model concerning key fatigue characteristics. • Extended phase field cohesive zone approach for fatigue simulation in concrete. • Comprehensive experimental validation under wide range of loading scenarios. • Unified approach for low- and high-cycle fatigue, pre- and post-peak cyclic behavior. • Suggestions for better fatigue simulations considering several fatigue key aspects. [ABSTRACT FROM AUTHOR]

• Review of numerical models for concrete fatigue under compressive loading. • Distinction of three classes of fatigue damage hypothesis for concrete compression. • Stress driven formulation of damage-plasticity model for fatigue simulation. • Comparison of selected modeling approaches to fatigue considering the sequence effect. In this paper an evaluation of existing numerical models for concrete fatigue behavior subjected to compressive loading is presented. The brief review of available modeling approaches is accompanied with their classification based on the postulated fatigue damage hypothesis and on the modeling scale at which the damage is introduced. Based on the review, three numerical models for concrete fatigue that are considered to be relevant for the simulation of high cycle fatigue are selected as representatives of different fatigue modeling hypotheses and evaluated in view of heir ability to reproduce several aspects of concrete fatigue behavior. The strengths and weaknesses of the studied numerical models are illustrated and discussed. Each model is presented by explaining its calibration procedure and showing its ability to reproduce the Wöhler curves, fatigue creep curves, energy dissipation, effect of loading sequence and computational efficiency. The discussion of the models includes also conclusions and suggestions for possible improvements of approaches to high cycle fatigue modeling. [ABSTRACT FROM AUTHOR]

• Review of experimental investigation of sequence effect on concrete fatigue. • Examination of Palmgren-Miner rule in view of experimental and numerical results. • Stress driven inelastic concrete model for efficient fatigue simulation. • Numerical investigation of the load sequence effect. • Engineering assessment rule for concrete fatigue considering the sequence effect. In this paper, a refined engineering rule for the assessment of remaining fatigue life of concrete under compressive cyclic loading with varying amplitudes is proposed. The rule has been derived based on a combined numerical and experimental investigation of the loading sequence effect. The applied modeling approach is based on a damage model using the equivalent tensile strain rate to govern the fatigue damage evolution upon loading and reloading at subcritical load levels. A systematic calibration and validation procedure of the numerical model was performed based on the available experimental results. The prediction of the numerical model was compared with existing damage accumulation rules for the assessment of the concrete fatigue life exposed to varying loading ranges. Based on these studies, an enhancement of the Palmgren-Miner rule is proposed and validated for several loading sequence scenarios. [ABSTRACT FROM AUTHOR]

In this paper we introduce a thermodynamically consistent bond-interface pressure-sensitive damage model with cumulative sliding strain measure as a fundamental source of fatigue damage. The modeling approach provides a clear physical interpretation of the dissipative mechanisms governing the propagation of fatigue damage within the concrete-steel/FRP interface so that it is possible to reproduce both the monotonic and the cyclic behavior of the bond with a consistent set of material parameters. The model has been applied for simulation of the degradation process in the bond between concrete and reinforcement bars and between concrete and FRP sheets under pullout fatigue loading. The paper presents numerical studies of the fatigue pullout behavior with detailed analysis of the damage propagation during loading and unloading stages, and at different levels of imposed lateral pressure. To validate the ability of the model, simulations of pullout tests published in the literature have been conducted. [ABSTRACT FROM AUTHOR]

For a reliable and economical design of concrete structures subjected to fatigue loading, a comprehensive understanding and realistic prediction of concrete fatigue life under complex loading scenarios with variable amplitudes is of major concern. In this paper, experimental investigations of concrete behavior under monotonic, cyclic, and fatigue loading are presented with particular focus on the influence of loading sequence on fatigue life. Namely, a test campaign consisting of 32 three-point bending tests on notched beams was conducted, including two beam sizes and six different loading scenarios. Several response characteristics of the fatigue behavior including, fatigue creep curves, Wöhler curves, stiffness degradation, evolving shapes of hysteretic loops, and crack propagation aspects have been evaluated. In addition, the main dissipative mechanisms governing the flexural behavior of concrete under repeated loading were analyzed based on a wide range of loading scenarios. Furthermore, the effect of loading sequence has been studied and analyzed in detail with the help of a 3D digital image correlation (DIC) system. Based on these observations, a theoretical interpretation of the phenomenology behind the sequence effect under bending loading is provided considering the fatigue crack propagation aspects and the corresponding stress redistribution around the crack tip. • Flexural fatigue behavior of concrete under a wide range of loading scenarios. • Review of experimental investigations of sequence effect on fatigue of concrete. • Critical evaluation of existing damage accumulation rules for flexural fatigue. • Fatigue crack propagation evaluation under variable amplitudes with DIC technology. • Consideration of fatigue crack growth in the interpretation of the sequence effect. [ABSTRACT FROM AUTHOR]

Mathematical modeling of fatigue behavior of concrete under compressive loading presents a challenging topic that attracts an increasing interest of the scientific community. The present paper proposes a new formulation of the microplane model referred to as MS1 aiming to capture the fundamental inelastic mechanisms that can reflect the tri-axial stress redistribution within a material zone upon cyclic loading at subcritical load levels. The key idea of the proposed approach is to link the fatigue damage evolution to the cumulative inelastic shear strain. In this way the accumulation of fatigue damage under compressive loading owing to internal shear/sliding between aggregates at subcritical load levels can be reflected. The present model is developed within the context of the microplane theory using a homogenization scheme based on the principle of energy equivalence with a direct tensorial representation of the effective elastic stiffness. The paper presents elementary studies of the model behavior accompanied with the evaluation of its capability to capture the response of concrete fatigue under compressive loading. A calibration and validation procedure of the model response is provided based on an accompanying experimental program including normal- and high-strength concretes subjected to several loading scenarios. The model shows the ability to reproduce the concrete behavior under monotonic, cyclic and fatigue loading with consistent set of material parameters. • A new formulation of the microplane model for concrete fatigue behavior under compression is proposed. • The phenomenon of tri-axial stress redistribution at subcritical fatigue loading levels has been captured. • Calibration and validation of the proposed model for normal- and high-strength concrete have been included. • Monotonic and fatigue damage propagation in both low and high-cycle fatigue regimes have been covered consistently. [ABSTRACT FROM AUTHOR]

In this paper, combined experimental–numerical investigations of the bond behavior between high-strength concrete and steel reinforcement under monotonic, cyclic and fatigue loading are presented. A modified beam-end test specimen is used to study the bond behavior under push-in compressive loading. The bond length, the concrete strength as well as the bar diameter have been varied in the test program consisting of 56 beam-end test specimens. The bond behavior has been tested under several loading scenarios and the results have been compared with the results of the pull-out tests. Push-through and combined push-through × splitting failure modes have been observed in the test program. Moreover, a bond fatigue model based on a cumulative measure of inelastic slip developed by the authors has been used to demonstrate how to identify the model parameters for a test exhibiting a pure push-through failure. The tests including three design parameters and four distinct loading scenarios will serve for further detailed theoretical research on the bond fatigue phenomenology governing the behavior of reinforced concrete structures. [Display omitted] • Modified beam end test for push-in loading with variable bond length. • High-cycle fatigue bond behavior between steel rebars and high-strength concrete. • Effect of the stabilized splitting cracks on the bond fatigue behavior. • Numerically reproduced trend of splitting crack effect on the bond fatigue behavior. [ABSTRACT FROM AUTHOR]

In spite of an extensive research in the past few decades, design of beams without shear reinforcement is still considered to be a challenging task. With the goal of developing realistic and simple engineering models, many researchers have contributed to the development of analytical and numerical approaches that have improved the understanding of the mechanical background of shear fracture. Still, some assumptions in these approaches, such as the rigid body kinematics which relies on the assumption of a uniquely identifiable center of rotation, have raised critical questions in the scientific community that need further consideration. In this paper, an automated crack detection scheme based on DIC-controlled modeling of damage localization is developed and presented. This scheme enables an automatic evaluation of opening and sliding profiles along the crack ligament, the center of rotation between two neighboring concrete teeth, and the moment–rotation curve directly from the DIC measurements of the surface displacement. To demonstrate the feasibility and the features of the developed scheme, verification studies are performed using tests performed on longitudinally reinforced concrete beams. The description of the mathematical concepts behind the developed crack detection scheme is accompanied with the explanation of the implementation method using modern Python packages for scientific computing, providing code snippets that show a straightforward translation of the mathematics into an executable code. Furthermore, a publicly available implementation of the developed scheme is provided in the form of an interactive Jupyter notebook. • Model and implementation concept for automated crack detection in RC shear zones. • Immediate evaluation of the opening and sliding profiles along crack ligaments. • Identification of the center of rotation between two neighboring concrete teeth. • Evaluation of rotational kinematics assumption of analytical models for shear zones. [ABSTRACT FROM AUTHOR]

A thermodynamically consistent model proposed in this work introduces a generative symbolic framework for computational components, which can capture the inelastic behavior of interfaces with 3D kinematics in response to monotonic, cyclic, and fatigue loading histories. It contributes to a long list of existing cohesive zone models by introducing novel forms of potentials for free energy, threshold function, and dissipation to deliver the following model properties: (i) the evolution equations derived from the potentials are linked in such a way that damage develops along with the cumulative measure of plastic sliding, (ii) the convex, continuous, and smooth shape of the threshold function introduced in the effective stress domain enables a general and efficient time integration that automatically handles unloading and reloading, and (iii) the non-associative flow potential includes a scalable degree of coupling between normal and tangential damage evolution. The studies performed in the paper demonstrate that these model ingredients lead to a consistent coverage of arbitrary non-proportional loading scenarios in tangential and normal directions. For monotonic loading, the presented examples illustrate the ability of the model to reproduce the shear dilatancy, pressure sensitivity including the vertex effect, stiffness recovery in compression, and abrasion due to sliding. For cyclic fatigue loading, the studies show that the model reflects the link between the hysteretic behavior and the fatigue damage evolution. This link constitutes the basis for a physically sound description of fatigue degradation along material interfaces. It manifests itself in the presented energy breakdown with distinguished fractions of energy release due to damage and plasticity ascribed to normal and tangential directions. Two calibration and validation examples using pull-out tests exposed to monotonic and cyclic loading are provided to show the applicability of the model for the characterization of the bond between steel bars and concrete. A publicly available implementation using a computer algebra system (CAS) is provided in the form of an interactive Jupyter notebook to document the reproducibility of the results. [ABSTRACT FROM AUTHOR]