Flexural behavior of ultra-high performance concrete (UHPC) shaped thin-plate ribbed staircases: an experimental and numerical study

To improve the transportation and lifting efficiency of precast staircases, a novel UHPC shaped thin-plate ribbed staircase was proposed and investigated under flexure by the accumulation load test. The flexural behavior of the proposed UHPC staircase was compared to the precast staircase made of Normal Strength Concrete (NSC), and the effects of fiber contents (0.75%, 1.0% and 1.5%) and the presence of steel bars in the UHPC staircase were experimentally investigated. The development of cracks and the comparison of load–deflection curves showed that the flexural behavior of the UHPC staircases was less susceptible to the disturbance of cracking than the NSC staircase. Besides, increasing the fiber content was beneficial to improve the crack resistance of the UHPC staircases, weaken the stress concentration effect of step roots on rib slabs, thereby improving the load-bearing capacity. The absence of rebar had no significant effect on the flexural behavior of UHPC staircases before cracking, but negatively affected the bending behavior after cracking. Furthermore, by means of the effective moment of inertia method and the introduction of a modified steel fiber conversion area parameter, a short-term stiffness model for UHPC stairs was proposed with a deviation within 6%. Finally, a parametric study was conducted based on a validated FE model, and suggestions are provided on the selection of section size to improve the flexural performance of the proposed UHPC staircases.