## 2 Review of Previous Studies of Steel Composite Bridge Shear Connectors
Static and fatigue tests were performed through single bolt shear tests using ASTM A325 bolts (nominal tensile strength of 830 MPa). Specifically, five million rounds of fatigue tests were performed at a bolt load of 175 kN and a shear stress range of 241 MPa. The results showed that shear resistance was similar to or better than those of conventional headed studs, and good performance was seen in terms of fatigue strength, as the shear connectors did not fracture even after five million rounds. Also, compared to the non-composite beam tests, the load bearing capacity increased by almost 50%, even at a shear connection ratio of less than 30%. [PERSON] et al. [28] studied the structural behavior of steel composite beam systems that use bolted shear connectors. It was recommended that a high-tensile force grip bolt (HTFBB) be used rather than a normal bolt shear connector to increase the shear performance. Citing the study results of other researchers, the ultimate strength of the composite beam with regard to HTFGBs was reported to be 66% of the tensile strength of high-tensile force bolt shear connectors. When grip bolts are used, initial slipping occurs in an amount equal to the clearance tolerance between the steel beam and precast concrete hole diameter and the shear connector diameter. A low level of shear force is resisted when the initial slipping occurs due to the friction of the contact surface between the steel beam and concrete and the load of the introduced bolts; then, after all of the slip equaling the amount of hole clearance has occurred, the direct shear resistance of the  
Figure 3: Demountable bolted shear connector types: (**a**) friction grip bolt; (**b**) without embedded nuts; (**c**) single embedded nuts; (**d**) double embedded nuts [21]; (**e**) LNSC [22]; (**f**) novel bolted connector [23]; (**g**) LBDSC [24]. shear connector, which is in a composite state, occurs. Accordingly, a load-slip prediction formula for HTFGB shear connectors in composite beams was presented. [PERSON] et al. [29] fabricated 12 bolted shear specimens and performed push-out tests to study the methods of designing bolted shear connectors for steel girders and precast concrete slabs. The major variables that influenced the shear resistance of the bolted shear connectors were considered to be the design strength of the precast slab, strength of the non-shrink mortar, stud diameter, and screw height, and the bedding layer height was fixed at 20 mm. A static strength assessment formula was presented as a function of the stud shear connector diameter and bedding layer thickness. The experimental results showed that when the nut height matched the bedding layer, reductions in static strength and fatigue performance occurred, but when the nut height was located within the bedding layer or slab, there was no great difference. This experimental research was used to propose a design formula that can be utilized when the nut height is within the bedding layer. [PERSON] and [PERSON] [30] used M20 bolts (level 8.8) according to Eurocode-4 to perform push-out tests on two specimens. A bolt load of 145 kN and a concrete compressive strength of 48 MPa were used. All bolts in both specimens fractured, and ductile behavior was seen due to a large amount of slip. It was concluded that this phenomenon was caused by the hole tolerance due to the slab being drilled at a diameter of 24 mm, which was larger than the bolt diameter of 20 mm. [PERSON] et al. [31] studied bolted studs using demountable shear connectors to replace welded studs. Eight push-out tests were performed on four studs with diameters of 19 mm and various concrete strengths, and it was confirmed that the slab could easily be demounted after the tests. The failure mode was shear fracture of the shear connectors and concrete crushing. The ductile behavior of the bolted shear connectors was excellent, but the stiffness was low and the shear resistance performance was similar to that of welded studs.