Analysis of the Bearing and Damage Mechanism in Steel–Steel Fiber–Reinforced Concrete-Composite Member

In order to avoid certain construction difficulties in a traditional steel reinforced concrete (SRC) structure, like the interference between reinforcing steel and rebars or poor concrete pouring quality, steel–steel fiber–reinforced concrete (SSFRC) was proposed by removing the steel rebars from SRC and incorporating steel fibers. According to a standard push-out test of 36 specimens, this paper studies the bearing and damage mechanism in the bond interface between steel and steel fiber–reinforced concrete (SFRC). The results show that splitting cracks usually elongate from the concrete surface to the interface while bonding cracks elongate from the tips of a steel flange toward the concrete surface in the 45° diagonal direction. The external loading is transferred to the bond interface through steel near the free end, forming the compression stress and bond shear stress, and then, those stresses at the interface are transferred to the bottom SFRC surface at the loading end through an inclined compression band inside the SFRC. The SFRC blocks separated by cracks achieved stress balance under the bearing stress from steel at the interface and the clamping stress from nearby SFRC blocks along the bonding cracks. The SFRC cover mainly takes the bending effect from the compression stress when the thickness of the concrete cover ranges from 19.5 to 40 mm in this paper, but it takes the shear effect when the thickness of the concrete cover is larger than 40 mm. It is worth noting that the flexural strength of the concrete with a steel fiber ratio (ρsf) of 3% is not significantly improved, but the ultimate bond strength is increased by 17.63% compared with that of ρsf=2%. In addition, the calculation formulas of the ultimate bond strength, including the chemical bond stress, mechanical interlocking stress, and frictional stress, are proposed.