Study on behavior of waffle-type UHPC-GFRP composite slab under three-point loading

The concrete in tension zone of traditional reinforced concrete bridge deck is liable to crack under vehicle loading, leading to easy corrosion of the internal steel rebars and earlier appearance of bridge disease. This study proposes a novel waffle-type UHPC-GFRP composite slab that can solve the cracking problem of traditional concrete bridge decks. The GFRP grid was partially embedded in the UHPC to transfer the shear force between the grid and UHPC. The remainder of the GFRP grid was exposed to form a ribbed structure similar to a "waffle plate". Five composite slab tests were conducted to investigate the mechanical properties of the proposed composite slab. Accordingly, the influences of the shear span-to-depth ratio, thickness of the UHPC layer, and embedded depth of the GFRP grid on the bending behavior of the composite slab were considered. The experimental results revealed three failure modes of the composite slabs: bending failure (the ultimate bending capacity of 81.1 kN), shear failure (the ultimate shear capacity of 147.8 kN), and GFRP interlaminar shear failure (the ultimate bearing capacity of 167.2 kN). The change in the shear span-to-depth ratio directly affected the failure mode of the composite slab. More specifically, the embedded depth of the GFRP grid increased by 10 mm, the cracking load and ultimate strength of the composite slab increased by 23.8% and 46.6%, respectively. Lastly, a calculation method for the new waffle-type UHPC-GFRP composite slab is proposed, and the calculation error is controlled to be within 12%.