Behavior of composite beams with UHPC-concrete composite slabs under negative bending moment

Enhancing the crack resistance of concrete slabs is crucial for advancing the application of steel-concrete composite beams. Therefore, this study investigated the flexural behavior of composite beams with UHPC-normal concrete (NC) composite slabs under negative bending moments through experiments, numerical simulations, and theoretical analysis. Initially, bending tests were conducted on four specimens with the UHPC layer thickness as the test parameter. The results revealed that UHPC effectively improved the cracking behavior of the slab. For composite beams with UHPC-NC slabs, the cracking load increased by 67 % compared to the beam with NC slab, while the ultimate load only decreased by 5–6 % compared to the beam with UHPC slab, despite a substantial reduction of 60–80 % in UHPC consumption. Subsequently, a numerical model of the composite beam with UHPC-NC composite slab was developed and validated against the test results. A parametric study demonstrated that flexural capacity increased nearly linearly with an increase in UHPC layer thickness or rebar ratio, and increasing the UHPC layer thickness also enhanced the flexural stiffness of composite beams. Finally, considering the tension contribution of UHPC, a calculation method for the flexural capacity of composite beams with UHPC-NC composite slabs under negative bending moments was derived and verified through experimental and numerical results. The utilization of UHPC-NC composite slabs significantly enhanced crack resistance while maintaining flexural capacity, providing a cost-effective and feasible solution to address slab cracking issues of composite beams in hogging moment regions.