Flexural fatigue mechanism of steel-SFRC composite deck slabs subjected to hogging moments

This paper aims to investigate the flexural fatigue mechanism of the steel-steel fiber reinforced concrete (SFRC) composite deck slab under hogging moments. Firstly, fatigue tests were implemented on two full-size slab specimens reinforced by different steel fibers, i.e. mill-cut steel fibers (MF) and corrugated steel fibers (CF). The failure mode, steel-concrete composite action, and crack behavior were measured and discussed. It finds that the fatigue failure of the composite slab under hogging moments was governed by the fracture of rebar in tension. Under service loads, the use of MF achieves lower stress amplitude of rebar in tension (Delta sigma(s)) by 6-9% and higher slab stiffness by 2-7%, compared with CF. Subsequently, both finite element and theoretical analysis are employed, through which the influence mechanisms of SFRC's strength parameters (f(L), f(R1), f(R3)) and slab's structural parameters on Delta sigma(s) are clarified, and the calculation method of Delta sigma(s) is developed. Results showed that Delta sigma(s) can be reduced by up to 7% with a 1.19 MPa increase in f(L) and by 12% as f(R1)/f(L) is raised by 0.4, whereas the effects of the f(R3) are minimal where a reduction of lower than 1% is obtained as f(R3)/f(R1) goes up by 0.4. The advantage of MF can be attributed to its better improvement on f(L) and f(R1) than CF. It also reveals that steel members with greater bending stiffness can attract higher moments, which decreases the moment sustained by the SFRC layer and thus reduces Delta sigma(s). The proposed calculation method yields satisfactory prediction accuracy and is capable of capturing the effects of strength and structural parameters.