Punching strength of flat plates reinforced with UHPC and double-headed studs

To verify the beneficial use of UHPC in the highly stressed region of column-slab connections, a total of ten punching tests on reinforced concrete slabs were performed. All interior column-slab connections included double-headed studs as shear reinforcement. Nine test specimens were in addition strengthened by fibre-reinforced Ultra High Performance Concrete (UHPC) units. These elements were built in around the columns in the slab compression zone, replacing there the normal strength concrete (NSC). UHPC units with three different diameters were applied. To allow for a flexible combination of UHPC unit and double-headed studs, most of the UHPC units were separated into four parts with joints in between and were provided with channels for the double-headed studs. The slabs including a UHPC element reached significantly higher failure loads than the test specimens without such an element. In the slabs including the UHPC units with smaller diameter, a clear punching shear failure outside the elements was observed. In the case of the larger UHPC units, significant cracks occurred inside the elements, indicating the initiation of a failure of the UHPC.