## 2 Review of Previous Studies of Steel Composite Bridge Shear Connectors  
Studies on shear connectors in steel girder and concrete slab composite bridges can be classified into those focusing on the welded style and the bolted style according to the joining style of the shear connector of the steel girder. Many studies have been performed on the welded style of shear connectors since the 1960s, mainly using styles with welded headed studs or Perfobond shear connectors, as shown in Figure 1.  
Various experimental and analytical research on headed studs in relation to welded style shear connectors has been performed over the past few decades. Based on the results of these studies, design formulas for shear connectors have been presented in the design standards of various countries. Recently, numerous studies on the group behavior of large-diameter studs and welded studs have been performed [1; 2; 3], and there have been many investigations of Perfobond rib shear connectors with.channels, \(\Gamma\) and L shapes [4; 5], and Y shapes [6]. [PERSON] et al. [1] and [PERSON] [2] studied easy slab removal and efficient precast slab shear pocket arrangement using welded connectors with diameters of 25-30 mm, i.e., larger than those of welded studs (19 or 22 mm), which are mainly used in steel composite bridges. [PERSON] [2] performed push-out tests on welded studs with a maximum diameter of 30 mm and compared the static and fatigue behavior results with the design formulas. Even when large-diameter studs were used, there were no problems with static strength or ductility, but the fatigue strength was slightly lower than that of normal studs, requiring improvements to the welding. In addition, it was concluded that the Eurocode-4 design strength can be applied even when using studs with large diameters of up to 30 mm. In order to use large-diameter (25-30 mm) shear connectors in steel composite bridges, [PERSON] and [PERSON] [3] performed push-out tests and FE analysis using ABAQUS to compare their design strength to that of conventional headed welded studs using Eurocode-4 and AASHTO LRFD [7]. They verified the FE analysis model using the results of push-out tests by [PERSON] and [PERSON] [8] and [PERSON] et al. [9] and presented an approach that uses FE analysis in detail. [PERSON] and [PERSON] [10] derived the shear strength assessment formula for a \(\Gamma\)-shaped Perfobond rib shear connector by performing experimental research and FE analysis using ABAQUS on shear specimens with \(\Gamma\)-shaped Perfobond rib shear connectors. During use, the connectors showed very strong stiffness, and they retained considerable ductility after reaching the ultimate load. The shear strength of the \(\
eg\)-shaped Perfobond rib shear connectors was determined by the effect of the ground pressure resistance on the concrete at the bottom of the shear connector, the effect of the dowel action of the concrete shaped by the rib hole, the effect of the transverse rebar, and the dowel effect at the rib head plate. In addition, studies on Perfobond ribs have been conducted by numerous researchers in South Korea, including [PERSON] et al. [11], [PERSON] and [PERSON] [12], [PERSON] et al. [13], and [PERSON] et al. [14]. [PERSON] et al. [13] proposed that through-rebars must be reinforced in order to improve usability and resolve reduced durability when Perfobond rib shear connectors are used in composite sections and there are holes. Figure 1: Shear connector types: (**a**) headed stud; (**b**) T and channel; (**c**) Perfobond. [PERSON] et al. (2022) performed push-out tests to assess the static behaviors of shear connectors with regard to lightweight concrete precast slabs. To prevent cracking in the bedding layer, which is a major cause of reduced strength in precast slabs that have bedding layers, a shear key was installed between the precast slabs and bedding layer, and the bedding layer was fixed in the transverse direction.