Abstract
A realistic prediction of the concrete fatigue life exposed to high-cycle loading scenarios with variable amplitudes is of utmost importance for a reliable and economically efficient design of civil engineering infrastructure for transport and energy supply. Current design codes estimate the fatigue life under variable amplitudes using the Palmgren–Miner rule, which assumes a linear scaling between lifetimes measured for uniform cyclic loading scenarios. Several experimental series conducted in the past, however, indicate that this assumption is not valid and that it may lead to unsafe design. In this paper, an experimental and theoretical investigations of the fatigue loading sequence effect in normal- and high-strength concrete behavior are presented, which confirm this observation. In particular, a test campaign with 135 cylinder specimens, including three concrete grades and six different loading scenarios has been conducted. Several response characteristics of the fatigue behavior including Wöhler curves, fatigue creep curves and evolving shapes of hysteretic loops have been evaluated. To substantiate the experimental results, a theoretical explanation of the observed sequence effect is formulated based on the assumption, that energy is dissipated uniformly within the volume of a test specimen during subcritical, compressive cyclic loading. Then, superposition of energy dissipation profiles along the lifetime measured for constant amplitudes becomes possible and a theoretical justification of the experimentally observed sequence effect can be provided. Moreover, a reverse sequence effect reported in the literature for bending fatigue of concrete can then be explained by an unevenly distributed energy dissipation over a cracked specimen. Supported by the theoretical consideration, the processed experimental data is used to validate existing fatigue life assessment rules by testing their ability to reflect the load sequence effect.
Highlights
The fatigue behavior of concrete has been usually investigated experimentally for loading scenarios with constant amplitudes
These studies of the loading sequence effect for compressive fatigue loading [6, 18,19,20,21] suggest the conclusion in relation to the P–M rule, (H–L) scenario leads to the fatigue life reduction while the (L–H) sequence results in an extension
Even though some experimental studies performed in the past indicated the existence of a load sequence effect in the concrete fatigue behavior, contradicting trends have been reported for compressive and tensile loads
Summary
The fatigue behavior of concrete has been usually investigated experimentally for loading scenarios with constant amplitudes. The experimental results presented by Tepfers et al [6], and Klausen [21] indicate a dependency of the fatigue behavior on the changed order of loading ranges, but due to the large scatter of the results clear tendency for the (L–H) and (H–L) sequences cannot be concluded [22, 23] These studies of the loading sequence effect for compressive fatigue loading [6, 18,19,20,21] suggest the conclusion in relation to the P–M rule, (H–L) scenario leads to the fatigue life reduction while the (L–H) sequence results in an extension. The current paper presents a comprehensive experimental investigation of the load sequence effect on the fatigue behavior and establishes a basis for its general theoretical energetic explanation It provides a qualitative validation using the extended P–M rule, previously proposed in [35]. 82 Page 4 of 23 the sequence effect are briefly reviewed and validated using the presented experimental results
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