Deformational behavior and damage mechanism of R-UHPFRC beam subjected to fatigue loading

Antoine Bassil, Eugen Brühwiler, Bartlomiej Wojciech Sawicki
2021
Journal paper

Abstract

The fatigue behavior of a reinforced UHPFRC (Ultra High Performance Fiber Reinforced Cementitious composite) T-shaped beam under four-point bending is investigated. The beam was subjected to a fatigue loading range equal to 49% of the static resistance and failed after 0.88 million cycles. It was instrumented with extensometers, strain gauges and distributed fiber optic sensors for strain monitoring. The fatigue process consists of three stages: with rapid, stable and again rapid growth of strains during 10%, 80% and 10% of total number of fatigue cycles, respectively. Except of the first 10%, this process takes place locally; therefore, it cannot be followed with the deflection measurement. During the stable stage, growth of strain occurs at minimum loading level in the fatigue cycle, indicating a fatigue damage process under tensile-compressive response of UHPFRC. Advanced fatigue crack propagation in the reinforcement bar determines the location of rupture of the beam. When the remaining cross-section of the rebar does not suffice to carry the tensile load, stress is transmitted to the encompassing UHPFRC causing its fast deterioration. Complete rupture of the rebar occurs only at the end of the test, when the beam collapses.

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Ultra-High Performance Fibre Reinforced Concrete (UHPFRC) combined with steel rebars, subsequently called R-UHPFRC, is a promising building material implying a novel technology for the improvement of concrete structures. Steel rebars enhance effectively the resistance of UHPFRC while reducing variability in the tensile behaviour of monolithic UHPFRC due to variation in fibre distribution and orientation. When a thin layer of R-UHPFRC is overlaid on top of a concrete bridge deck slab, it is subjected to repeating wheel loads and fatigue limit state needs to be considered. This paper presents the results of tensile fatigue tests on R-UHPFRC elements for the determination of its fatigue behaviour. Experimental results show a fatigue endurance limit at 10 million cycles at a solicitation level of S = 0.54 for S being the ratio between the maximum fatigue force and the ultimate strength. Over the fatigue life of the specimens, stress was transferred from UHPFRC to steel rebars. Fatigue resistance of R-UHPFRC shows that it has a significant potential for fatigue strengthening of reinforced concrete structural elements like bridge deck slabs.

2014

Ultra-High Performance Fibre Reinforced Composites (UHPFRC) is a cementitious material showing relatively high tensile strength and significant tensile strain-hardening behaviour (given a certain volume of fibres). Adding a layer of UHPFRC or UHPFRC combined with steel rebars (R-UHPFRC) to structural members is an efficient method for strengthening of reinforced concrete structures. This paper presents empirical fatigue damage models for UHPFRC and R-UHPFRC. The tensile fatigue behaviour of UHPFRC is analysed based on elementary damage mechanics theory. Damage grows at a constant rate until fatigue fracture, which is considered to be due to the capacity of UHPFRC to redistribute local deformation increases. Difference in damage evolution between fatigue fracture tests and run-out fatigue tests is highlighted, and it is understood that when significant damage is caused in UHPFRC in the early stage of the fatigue life, UHPFRC fractures due to tensile fatigue. An average curve of damage evolution of fatigue fracture tests is proposed as a bi-linear damage evolution model of UHPFRC. The damage evolution model is used to determine the remaining fatigue life of UHPFRC by correlating the damage-fatigue strain relationship for UHPFRC. Considering that stress transfer from UHPFRC to steel rebars is characteristic of the R-UHPFRC tensile fatigue behaviour and is caused by fatigue damaging of the UHPFRC part, evolution of the modulus of deformation, i.e. the ratio of stress to strain of the UHPFRC part of the R-UHPFRC specimens is investigated. Among all the R-UHPFRC specimens similar behaviour is observed in the fatigue damaging curves of the deformation modulus of the UHPFRC part. An empirical relationship between the modulus of deformation of the UHPFRC part in the R-UHPFRC element and the number of fatigue cycles is proposed to characterise the R-UHPFRC tensile fatigue behaviour. (C) 2015 Elsevier Ltd. All rights reserved.

Elsevier Sci Ltd2015