The effect of fatigue loads on one of the main mechanical properties of fiber-reinforced high strength concrete (FRHSC) is studied in this work. In particular, this paper analyzes the variations in the residual tensile strength of steel fiberreinforced concretes following cyclic flexural loading, which causes a predefined level of damage. To do so, a total of 40 prismatic specimens were tested. The specimens were not notched, but had previously been subjected to precracking. This has a similar effect to notching, but with a much smaller radius around the edge of the crack, which is therefore more vulnerable to fatigue. The results show that the damage provokes a progressive reduction in the residual traction strength. The study proposes two numerical expressions for the stress-crack width softening curves under tensile loads: an exponential formulation and a potential formulation. In both cases, the coefficients of both formulations depend on the damage that is induced. In addition, the proposal is to use fitted curves of the above-mentioned potential type.
This paper discusses the residual modulus of elasticity of and maximum compressive strain in high‐strength concrete (HSC) and fibre‐reinforced high‐strength concrete (FRHSC) after being subjected to axial high‐stress‐level cyclic loading. The paper presents a specific procedure for evaluating the residual values of these mechanical parameters of concrete specimens.This procedure reveals that there is no monotonic decrease in the residual modulus of elasticity with number of cycles; an initial decrease occurs in all cases, followed by an increase and, finally, another decrease. Similarly, there is no monotonic increase in the residual maximum compressive strain.The results show substantial changes in both the residual modulus of elasticity of and the residual maximum compressive strain in concrete depending on the number of cycles. These variations are due to the combined action of two concrete phenomena: microcracking and reconsolidation of the concrete microstructure.
Fatigue is the process of mechanical degradation of a material, which leads to its collapse. Repeated load applications with a maximum value lower than the one that provokes the static failure of the material, causes internal damage in the material that, progressively, reduces its mechanical capacity until it finally collapses. The increasingly widespread use of high-strength concretes permits the construction of more lightweight structures. This implies that the variable loads (which are the causes of fatigue) represent an ever larger percentage of the total load. In consequence, fatigue is an increasingly important factor in concrete structures. In some cases, it even begins to be the dimensioning load of the structure. In addition, the presence of fibers within the concrete modifies the fatigue response of the concrete. In this chapter, the classic theory of fatigue is presented in detail and the most recent developments in the study of concrete fatigue are discussed.
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