Uneven distribution of interfacial bond stress in steel fiber-reinforced concrete-encased steel composite structures

To solve the congestion of reinforcement and the difficulty of concrete pouring in concrete-encased steel (CES) structure, steel fiber-reinforced concrete-encased steel (SFRCES) structure was proposed. Push-out tests of 34 SFRCES specimens were carried out in this paper to study the interfacial bond stress distribution, and load-displacement curves were obtained. The interfacial ultimate bond strength calculated based on load-displacement curve is much greater than 0.2 MPa which is the interfacial design shear strength of composite steel and concrete structure in Eurocode 4. This illustrates that the design of SFRCES structure is partial to safety. Furthermore, different from the previous method using the assumption of uniform distribution of interfacial bond stress, the interfacial local bond stress was obtained based on strain data and mechanical derivation in this paper. Moreover, the influence of steel fiber volume rate, embedded length of steel, and thickness of concrete on the distribution of interfacial bond stress was analyzed by defining the uneven coefficient of interfacial bond stress distribution. Analysis results provide a theoretical basis for the design of SFRCES structure and lay a foundation for the application of SFRCES structure in practical engineering.