Punching Shear Enhancement of Flat Slabs with Partial Use of Ultrahigh-Performance Concrete

Abstract

Previous studies have clearly shown that flat slabs made of ultrahigh-performance concrete (UHPC) have considerably higher punching shear strength than their counterparts made of conventional concrete. However, it may not be economically feasible to construct an entire slab out of UHPC. As such, the objective of the research reported in this paper was to determine the optimal use of UHPC within the critical punching shear area, while the remainder of the slab is made of normal concrete. Ten flat slab specimens with two different steel reinforcement ratios and three different areas (or depths) of UHPC were tested under a concentric load to study the effect of UHPC on punching shear capacity of flat slabs. Test results showed that full-depth application of UHPC within the area enclosed by a perimeter located at a distance equal to the slab thickness from the column face could enhance punching shear capacity of the slab by 70%. This configuration was deemed to be the optimal application of UHPC in flat slabs. On the other hand, half-depth application of UHPC does not significantly improve shear capacity of flat slabs. The research reported in this paper also questioned the applicability of two available punching shear models for flat slabs made fully or partially out of reinforced UHPC.