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

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.