Fatigue behaviour of a normal‐strength concrete – number of cycles to failure and strain development

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Damage processes in dynamically loaded concrete structures depend on the number and amplitude of applied load cycles. Damage evolution is linked to a reduction in concrete stiffness, and it is thought that this reduction causes stress redistributions at the component level, which have a favorable impact on the service life of the structure. Until now, the stiffness reduction and stress redistribution have never been successfully measured in laboratory tests or in situ. It is only known that the real service life is greater than the calculated one and that indicators of stiffness reduction, such as the component deflection, increase with the number of applied load cycles.Ultrasonic measurement techniques are considered to be well suited for detecting degradation processes caused by dynamic loading. By using ultrasonic pulse velocity measurements, it is expected that the stiffness reduction of dynamically loaded concrete structures can be recorded reliably. Against this background, fatigue tests on small-scale concrete specimens were performed. The aim of the tests was to understand the correlation Accepted Article www.ernst-und-sohn.de Page 2Structural Concrete between the observed stiffness degradation of the specimens and the results of ultrasonic pulse velocity measurements and to estimate the potential of ultrasonic pulse velocity measurements for continuous structural health monitoring.

Section: Ultrasonic Investigations Of Fatigue Loaded Concrete Specimensmentioning

confidence: 99%

Development of stiffness and ultrasonic pulse velocity of fatigue loaded concrete

Haar

Marx

2016

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“…The bond behavior of reinforcement under cyclic loading is similar to fatigue behavior of concrete under compression and follows an S shape curve (Figure ). Relationship between slip of reinforcement and number of loading cycles under unidirectional constant amplitude cyclic loading can be divided into three stages (Figure ): development of reinforcement slip is faster during the first loading cycles at the first stage (A–B); increase of slip of reinforcement in the second stage becomes constant (B–C); slip of reinforcement rapidly increases up to the failure of bond between reinforcement and concrete (pullout failure) in the third stage.…”

Section: Analysis Of Models Of Bond Between Reinforcement and Concretementioning

confidence: 70%

Influence of cyclic loading and frost on the behavior of bond of three‐wire strand

Jokūbaitis

Marčiukaitis

Valivonis

et al. 2018

This paper presents the results of an experimental research investigating the influence of static and cyclic loading and frost impact on the bond between concrete and 6.2 mm three‐wire‐strand. From the pullout tests, it was determined that a cyclic load did not negatively influence the bond strength of three‐wire strand. On the contrary, the influence of cyclic loading after 200 freezing and thawing cycles resulted in a significant decrease of bond strength of three‐wire strand. Additionally, the new parameters for bond stress–slip relationship suggested in Model Code 2010 are proposed for the 6.2 mm three‐wire strand cast with concrete having compressive strength of 82.6 MPa with standard deviation of 6.65 MPa. The results of dynamic coefficient b for 6.2 mm three‐wire strand used in relationship between a slip of reinforcement and a number of loading cycles under unidirectional cyclic loading suggested in Model Code 2010 are analyzed.

“…The measured temperatures of selected specimens are shown in Figure 5 of Reference . The temperature increase is a result of the cyclic loading and not of an external temperature increase.…”

Section: Resultsmentioning

confidence: 99%

“…The increase in specimen temperature was measured with thermo elements, which were located at the upper and lower rim and at midheight of the test specimen. A more detailed account of the test execution is given in Reference .…”

Section: Test Executionmentioning

confidence: 99%

“…Larger ultimate fatigue strains were measured in tests with longer test durations than in tests with shorter test durations, where both the longer and shorter tests had the same maximum and minimum stress levels ( S max ; S min ) but differing load frequencies f p . Furthermore, a temperature increase occurs in the specimens during fatigue tests due to the cyclic loading . The temperature increase induces thermal strains.…”

Section: Introductionmentioning

confidence: 99%

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A strain model for fatigue‐loaded concrete

Haar

Marx

2017

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Funding informationDeutsche Forschungsgesellschaft (DFG) "Extension and Verification of an Energetic Fatigue Model of Cyclic Loaded Concrete".In this contribution, an additive strain model is used to describe the deformation behavior of concrete. The model assumes that elastic, viscous, thermal, and damage-induced strains occur in concrete. The strain components develop independently of each other as a function of the number of load cycles, test duration, and characteristic parameters of the stress cycles. The focus of this paper is on the determination of a creep-relevant stress level to estimate the magnitude of the viscous deformation component as a function of the fatigue stress. Experimentally measured strains of fatigue-loaded concrete specimens are divided into the strain components assumed by the additive strain model and analyzed. The investigations yield new insights into the strain and material behavior of fatigue-loaded concrete. K E Y W O R D S additive strain model, concrete, creep-relevant stress level, fatigue loading, strain behavior