# Shear Behavior of Superposed Perfobond Connectors Considering Lateral Constraints
## 1 Introduction  
Steel-concrete composite structures are a new version of conventional steel and reinforced concrete structures. They combine the advantages of steel and concrete materials, offer improved mechanical performances, and yield better economic benefits. Connectors play a crucial role in realizing the combined properties of steel and concrete. At present, headed stud connectors are widely used [1, 2]. [PERSON] et al. [3] first proposed a new connector (referred to as the perfobond connector), which was constructed by welding a perfobond rib to the flange of the steel beam and inserting the rebar through the hole. After the concrete is poured, the concrete dowel and perforating rebar in the hole can transmit the longitudinal shear force and resist vertical lifting between the concrete and steel. Previous studies have shown that perfobond connectors offer convenient construction, good shear performance, and superior fatigue performance [4, 5, 6]. Two primary types of perfobond connectors are currently in use: the superposed perfobond connectors for composite structures and the inserted perfobond connectors for bridge construction. Their structural forms are shown in Figure 1a,b, respectively. Push-out tests and numerical simulations are typical methods for studying inserted perfobond connectors. Using these, the calculation equation for the connector's shear capacity can be derived through regression fitting. [PERSON] et al. [7] studied the mechanical properties and proposed an analytical model for calculating the shear capacity of perfobond connectors with different plate thicknesses. [PERSON] et al. [8] developed a shear equation that could simultaneously estimate the shear capacities of studThe equation obtained by [PERSON] et al. [9,10] incorporated the shear action of the concrete dowel, perforating rebar, and interface bonding. [PERSON] et al. [11,12] carried out push-out tests and finite element analysis on 13 groups of PBL connectors and proposed a formula for calculating the bearing capacity considering the constraints of external concrete and the transverse reinforcement, in which the contributions of the concrete dowel and perforating rebar were nonlinear. A typical load-slip curve of the inserted perfobond connector is shown in Figure 2. Its shear capacity is seen to be relatively high, owing to the strong confinement of the concrete dowel. A negligible decline period can be seen during the curve's loading process, demonstrating the inserted perfobond connector's excellent load-holding ability. The previous studies on superposed perfobond connectors can be primarily divided into three categories: (1) [PERSON] and [PERSON] [13, 14, 15], [PERSON] et al. [16], [PERSON] et al. [17], [PERSON] et al. [18], and [PERSON] et al. [19,20] conducted push tests and numerical analyses on connectors, considering the concrete end-bearing effect; (2) [PERSON] and [PERSON] [21] performed an experimental study taking into account the chemical bond between steel and concrete; (3) [PERSON] et al. [6], [PERSON] et al. [22], [PERSON] and [PERSON] [23], and [PERSON] et al. [24] studied connectors by neglecting the concrete end-bearing effect and chemical bond, by means of push-out tests and finite element nonlinear analysis. Numerous scholars have analyzed the mechanical properties and failure mechanisms of all types of connectors. Then, the shear capacity equations have been proposed via parameter analysis  
Figure 1: Typical perfobond connector specimens: (**a**) Superposed perfobond connector; (**b**) Inserted perfobond connector. Figure 2: Typical load–slip curves of two connector types. and regression fitting. The parameters mostly include the number of holes, hole sizes and shapes, concrete compressive strength, diameter of the perforating rebar, and so on. As shown in Figure 2, research regarding the load-slip curves of superposed perfobond connectors indicate that their capacity is lower than that of inserted perfobond connectors because of the weak constraints of the concrete dowel.