## 2 Review of Previous Studies of Steel Composite Bridge Shear Connectors
[PERSON] [21] investigated the shear performance and ductile behavior of bolted shear connectors for use in precast concrete. They conducted a review of literature in related fields, a preliminary investigation, and various push-out tests on shear specimens and presented a satisfactory analytical approach regarding the experimental results using FE analysis and various variable studies. The failure modes and mechanical behaviors of welded studs and bolted shear connectors were compared in detail through an analytical approach. [PERSON] and [PERSON] [32] used push-out test specimens with steel girder and fiber reinforced plastics (FRP) composite slabs to assess the shear loads, stiffnesses, and ductile behaviors of demountable bolted shear connectors. Ajax, Lindapter Hollo-Bolt, and injected steel-reinforced resin (SRR) connectors were used as the demountable bolted shear connectors for comparison. The failure mode and load-slip behavior of each shear connector were assessed and compared with the FE analysis results. [PERSON] and [PERSON] [22] proposed a locking nut shear connector (LNSC) that manufactured a conical nut with a tapered lower surface of the nut embedded in a concrete slab to minimize slip and fastened it to the tapered hole of the upper flange of a steel girder. In addition, for the synthesis of a precast concrete slab and steel girder, a method of synthesizing using separately manufactured plug concrete, a plate washer, stud head and nut, and grouting was applied to the shear pocket. Push-out tests showed that shear resistance, stiffness, and slip capacity were significantly higher than weld studs, along with good stiffness and strength against slab lift. In most failure modes, shear failure occurred at the stud bolt thread on the top of the buried nut. The authors also proposed a design equation for predicting shear resistance with an absolute error of less than 8%. Although this method shows excellent performance in terms of initial slip and stiffness raised as problems with general bolt-type shear connectors, it is expected that the manufacturing process will be extremely complicated because there are many of these third-part elements in practical field application. In the case of some specimens, inconsistent load-slip behavior is considered to be influenced by the manufacturing process of these various members. [PERSON] et al. [23] proposes a novel bolted connector method using a bolt fastened to the flange hole of a steel beam and a bolt embedded in a concrete slab, that is, two high-tensile bolts,albeit connected with a coupler such that these bolts can be combined within the concrete slab. The influence of bolt strength, diameter, and flange hole tolerance was examined through push-out tests. In the case of the concrete slab, negligible damage was observed and the failure occurred where the bolts connected to the steel beam flanges. In the case of the welding stud method, slip displacement of about 8 mm occurred; however, most of the cases where the novel bolted connector was applied showed a tendency to break with a small slip deformation of less than 5 mm. The maximum slip under the breaking load increased as the bolt diameter increased. Furthermore, the authors suggested that little correlation exists between shear stiffness and bolt diameter and strength, while shear stiffness tends to decrease as the tolerance between bolt shank and bolt hole increases. [PERSON] et al. [33] proposed a method using an embedded mechanical coupler device as a demountable stud connector. This was reported by [PERSON] et al. [23]. It is similar to the novel bolted connector method proposed by [23]. In addition, it was compared with the friction-grip bolt type including a cylinder system in a concrete slab. The overall failure mode was shear failure of the bolt, bearing deformation in the steel beam flange hole, and damage to thread penetration.