Experimental Investigation of Flexural Behavior of Steel–UHPC Composite Beam with Waffle-Slab System

The flexural behavior of steel-ultrahigh performance concrete (UHPC) composite beams with waffle slabs (SUCBWS) was investigated through experiments. The effects of design parameters, including the ratio of rib height to upper panel thickness, ratio of width to spacing for longitudinal rib, ratio of transverse rib spacing to longitudinal rib spacing, waffle-slab height, and the arrangement of studs, were evaluated by six specimens. The crack propagation of UHPC, failure mode, load-deflection relationship, strain distribution of main cross sections, and relative slip between the steel beam and the waffle slab were analyzed. The results showed that SUCBWS was characterized by obvious bending failure and good ductility. The composite beam achieved its flexural strength without obvious longitudinal splitting cracks on the waffle slab, even for the transverse reinforcement ratio of 0.33%. As the ratio of width to spacing for longitudinal rib and the ratio of transverse rib spacing to longitudinal rib spacing increased, the stiffness and integrity of waffle slab was weakened. Finally, the transformed section method was developed to calculate the elastic flexural capacity of SUCBWS.