Experimental investigation on punching resistance of R-UHPFRC–RC composite slabs

An effective method to strengthen existing Reinforced Concrete (RC) structures is to add a thin layer of Ultra-High Performance Fiber Reinforced cement-based Composite (UHPFRC), with or without steel rebars, over the concrete slab to create a composite element. It was demonstrated by previous test series that this method increases rigidity, bending and shear strength of one-way RC members. This paper presents the results of punching tests on 6 composite slabs without transverse reinforcement. The parameters of the tests included the thickness of the UHPFRC layer and the amount of reinforcement in it. All slabs failed in punching mode with a drop in resistance after maximum resistance was measured. For a layer of 50 mm of UHPFRC, the normalised resistance was at least 1.69 times greater than the normalised resistance of the RC reference slab. The layer of UHPFRC increased the rigidity of the slab and provided added shear resistance to the cracked RC section by out-of-plane bending. By doing so, it allowed more deformation to take place in the RC section before punching shear failure. This results in rotations and deflections at maximum resistance similar to what was observed for the reference RC slab.