The interface slip between shape steel and concrete is one of the biggest problems in numerical simulation of composite structures, this paper aims to investigate interfacial bond-slip behavior between steel and steel fiber reinforced concrete. For this purpose, a series of push-out tests on 15 circular section specimens which were designed and fabricated with different steel fiber ratio, interface embedded length and concrete cover thickness have been done. Experimental results show that average bond strength versus free end slip curves of each specimen is similar, and then a basic average bond strength-free end slip constitutive model was proposed in this paper. Meanwhile, considering the distribution regularities of steel strains, local bond strength and relative slip along the interface embedded length at different load levels were obtained through the mechanical derivation, the results show that the maximum local bond strength was located near the free end, and the local bond strength away from free end tended to be steady. Based on the basic average bond strength-free end slip constitutive model, two position functions were proposed to describe the local bond-slip constitutive model considering the variation of positions. Two position functions are of great significance for further research on SSFRC non-linear properties by FEM.

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To address the problems faced with steel-reinforced concrete (SRC) in construction, such as positional conflicts between steel and steel bars or difficulty in pouring concrete, a novel "Steel and Steel Fiber-Reinforced Concrete" (SSFRC) composite structure was proposed. Push-out tests of 34 SSFRC composite columns were carried out in this paper to study the interfacial bond performance from the perspective of energy dissipation. Based on loading-displacement (P-D) curves, the interfacial energy dissipation (W b ) and energy dissipation factor (λ) were introduced, and the influence of embedded length (L e ), steel fiber volume rate (ρ sf ), thickness of concrete cover (C ss ), and section type on W b and λ were analyzed. Test results indicated that circular column is better than square column in terms of W b and λ. The increase of L e , C ss , or ρ sf is beneficial to the improvement of W b , and λ is positively correlated with ρ sf and C ss but negatively correlated with L e . Additionally, the interfacial damage (D a ) was defined by the relationship between elastic deformation energy (W a ) and W b . It can be concluded that the ascent of L e and C ss can effectively delay the appearance of D a and inhibit the development of D a , respectively, and D a develops slowly with the increase of ρ sf at the later loading stage.

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Summary According to the construction difficulties in steel reinforced concrete (SRC) structures, rebar cages were discretized into steel fibers to form steel and steel fiber reinforced concrete (SSFRC) structures. The 18 SSFRC beams without rebar cages were tested under bending, and the effect of the steel fiber volume ratio (ρsf), shaped steel ratio (ρss), and shear span ratio (λ) on mechanical properties were investigated. Increasing ρsf could not only turn shearing failure and debonding failure into bending failure, and effectively reduce the sudden decrease of load, but also enhance the bearing capacity, ductility, and damage resistance of specimens to a certain extent. As the ρss ascended, the mechanical properties were obviously improved. However, ρsf should be accordingly increased to avoid adverse effects of excessive ρss. The specimen with small λ had the better bearing and energy dissipation capacity and poor ductility. A large λ meant that ρss and ρsf should be appropriately increased to prevent premature failure of specimens.