## 3 Interfacial Shear Distribution of Shear Connectors in Tensile Region of SC Composite Beam  
Based on the existing research on the out-of-plane flexural behavior of SC composite beams, the interfacial shear distribution of shear connectors could be divided into three phases: in the first phase, the concrete was uncracked and the shear connector was elastic; in the second phase, the concrete was cracked and the shear connector was elastic; in the third phase, the concrete was cracked and the shear connectors or steel plate yielded. For the sake  
Figure 5: Simulation for hysteretic curves and skeleton curves of SC composite beams. (**a**) Hysteretic curve of SCB1; (**b**) skeleton curve of SCB1; (**c**) hysteretic curve of SCB2; (**d**) skeleton curve of SCB2. of simplicity, the following assumptions should be allowed: (1) plane section assumption; (2) ignorance of interfacial friction; (3) infinite axial stiffness of shear connectors at the interface; and (4) neglection of shear deformation. The shear-slip curves of shear connectors and the constitutive model of steel-plate were assumed to be bilinear. The interfacial shear distribution of a cantilever SC composite beam subjected to concentrated load at the free end was investigated, as shown in Figure 6.  
According to the research provided by [PERSON] [11] and [PERSON] [25], when the concrete was uncracked and shear connectors were elastic, the interfacial slip distribution curve of the shear connectors was approximately parabolic. Due to the lower tensile strength of concrete, the interfacial slip in this stage could be very small. The shear connectors were assumed as elastic, so the interfacial shear distribution could be approximately parabolic. Based on the simulation results of the SC composite beam, the interfacial shear distribution of tie-bars in the SC composite beam is measured and shown in Figure 7b. When the concrete is cracked, the steel plate and shear connectors are still elastic, and the interfacial slip distribution of shear connectors should be trapezoidal due to the occurrence of vertical cracks in concrete. The concrete cracks occurred and widened with the increase in loading. The difference between the reinforced concrete beam and SC composite beam is that the cooperative deformation of concrete and longitudinal rebars in reinforced concrete beam depend on the end anchorage of rebars and the rib on the surface of rebars, and the cooperative deformation of concrete and steel plate in the SC composite beam only relies on shear connectors. Thus, the vertical cracks usually occurred around shear connectors. The authors conjectured that the slip of shear connectors was approximately equal to the summation of the width of cracks between the shear connector and the fixed end. Thus, the interfacial slip distribution of the shear connectors could be trapezoidal, and the turning point was close to the farthest crack, as shown in Figure 8. The shear connectors were assumed to be elastic, so the interfacial shear distribution could be approximately trapezoidal. With the increase in loading, the width and number of cracks increased, and the location of the latest crack was further from the fixed end. According  
Figure 6: Schematic of cantilever SC composite beam. Figure 7: Distribution of interfacial shear slip of SC composite beams in the condition that concrete was uncracked. to the simulation results, the interfacial shear distribution of tie-bars in the SC composite beam is measured and shown in Figure 8b. Based on the interfacial shear slip distribution, bilinear shear-slip curves of shear connectors, and bilinear constitutive model of the steel plate, when all the shear connectors were yield or the tensile steel plate was yield, the shear connection degree could be divided into three levels: low, middle, and high. For the low level, before the tensile steel plate was yield, all the shear connectors were firstly yield. For the middle level, before the tensile steel plate was yield, some shear connectors were yield.