Flexural Performance of Ultrathin UHPC Slab–Steel Composite Beams with Ultrashort Stud Connections

Abstract

To optimally use the excellent mechanical properties of ultrahigh performance concrete (UHPC), this study experimentally investigated the flexural behavior of 10 lightweight steel-UHPC composite beams constructed using thin UHPC slabs and ultrashort studs. The influences of stud spacing, slab thickness, stud aspect ratio (height-to-diameter ratio), and shear span ratio on moment capacities, postcracking and postyielding strength, and deflection increments were investigated, along with the observations of failure modes, crack patterns, strain distributions, slip/uplift behavior, and unloading response after failure. Experimental results indicated a 9% decrease in the moment capacity with a 22% larger ultimate deflection as the full shear connection degree decreased to 0.5. A decrease in the stud aspect ratio from 1.5 to 1.0 caused similar loads but 45% larger ultimate deflections due to the uplifting and splitting behavior of the composite beams. An increase in the thickness of the UHPC slabs from 35 to 55 mm increased the postyielding strength and deformability by relieving the local UHPC crushing failure. With only half and one-third the thickness of normal concrete slabs, the 35- and 55-mm-thick slabs provided an elastic flexural stiffness similar to and 26% higher than that of the composite sections, respectively, with higher ductility. The current design code accurately predicts the bearing capacity of ultrathin UHPC–steel composite beams. In future research, the coupling effects of both interfacial slip and uplift on the overall deflection of such composite systems should be investigated.