Mechanical behavior of natural bonding interface in hollow steel-UHPC composite bridge deck

The hollow steel-UHPC (Ultra-high performance concrete) composite deck with interfacial connection by natural bond is a new type of deck with simple appearance and high-stress efficiency. However, the interfacial bonding properties of this composite deck and their effect on the structural performance remain unclear. In this study, the shear tests under different interface sizes, curing conditions and interface states were carried out to analyze the interfacial bonding properties between UHPC and steel tube in composite deck. Besides, the finite element model was used to further study the influence of different interface behaviors on the mechanical properties of composite deck. Results indicated that the whole failure process of UHPC-steel tube composite specimens included the elastic stage, the interface bond failure stage and the friction stage. The ultimate strength of composite specimens would not completely be lost when they failed, since there was also residual interface strength provided by friction. The influence of curing conditions on the interface strength was most significant. The ultimate load of composite deck was increased by 13.69% when the interfacial bonding strength was increased from 0.5 to 4 MPa. However, the influence of interfacial stiffness on the mechanical behavior of composite deck was negligible. When the interfacial fracture energy was increased from 1.4 to 4 N/mm, the ultimate load of composite deck was increased nonlinearly and slowly by 13.87%. Finally, there was little effect on the performance of composite deck when the interfacial bonding strength exceeded 4 MPa or the fracture energy was larger than 4 N/mm.