## 1 Introduction  
In a steel-concrete composite structure, the interfacial shear distribution of ductile shear connectors, for example, studs, was usually assumed to be uniform between the maximum bending moment and zero bending moment for the sake of convenience in construction [1; 2; 3]. The ratio of the number of shear connectors provided to the number of shear connectors calculated is called the shear connection ratio (\(\gamma\)). When \(\gamma\) reaches 1.0, it means the total of shear capacities of the shear connectors is equal to the smaller value between the yield capacity of the steel beam and compressive capacity of the concrete plate, and it is called full shear connection. In the 1990s, the steel plate-concrete (SC) composite structure was developed by [PERSON] et al. [4], which was used in submerged tube tunnels. A SC composite structure includes two thin steel plates, concrete core, and connectors. Due to the modular construction, eliminating formwork, and superior mechanical properties, the SC composite structure is widely used in high-rise buildings, nuclear power plants, bridges, tunnels, cargo tanks, hulls, and offshore oil platforms. For the SC composite structure, the \(\gamma\) is also an important index. [PERSON] et al. [5; 6] carried out an experimental study on the flexural behavior of SC composite beams with long studs and short studs; the experimental results indicated that when the \(\gamma\) is close to 2, the flexural capacities of SC composite beams can reach the theoretical value at the state of yield of the tensile steel plate. [PERSON] et al. conjectured that the cracks and partial crush of concrete at the bottom weaken the shear capacities of studs, so the shear capacities of studs should be decreased by 50%. [PERSON] and [PERSON] [7] investigated the flexural behavior of SC composite beams with one steel plate subjected to monotonic loading. The experimental results indicated that, when \(\gamma\) reaches 1.6, the bending moment of the SC composite beam can reach the theoretical value. [PERSON] et al. [8,9] measured the interfacial shear and interfacial shear slip in SC composite beams with studs. The experimental results indicated that the interfacial shear and interfacial shear slip at the middle are almost neglected, and they are significantly higher at the end. The phenomena were also verified in other research works [10,11]. Currently, in two specifications, AASC/ANSI N690s-15 [3] and JEAC 4618-2009 [2], the design for shear connectors in SC composite beams are stipulated. In JEAC 4618-2009, the interfacial shear distribution of shear connectors is also assumed to be uniform. In AASC/ANSI-N690s-15, the shear connectors should be divided into ductile shear connectors and nonductile shear connectors. For ductile shear connectors, the interfacial shear distribution can be assumed to be uniform, and for nonductile shear connectors, the interfacial shear distribution can be assumed to be triangular. The authors carried out push-out tests to investigate the shear behavior of tie-bars and studs under monotonic and cyclic loadings [12,13]. They showed that the failure mode of tie-bars under monotonic and cyclic loadings are ductility and brittleness, respectively. The shear capacities and ultimate shear slip of tie-bars under cyclic loading are far below those under monotonic loading. In addition, tie-bars in a SC composite structure not only offer interfacial shear between the steel plate and concrete, similar to studs, but also improve the out-of-plane shear capacity of the SC composite structure, like stirrups in a reinforced concrete beam. The author investigated the influence of axial tension on the shear capacities of tie-bars under cyclic loading and proposed a formula for calculating the relationship between shear capacities and the tensile capacities of tie-bars [14].