## 3 Push-Out Tests and Analysis of Results  
### Shear Specim Fabrication and Material Properties  
Generally, when performing strength assessment experiments on the shear performance of steel composite bridges, push-out tests using shear specimens are generally performed rather than composite beam experiments. In South Korea, no clear push-out test regulations have been established, but many researchers follow the testing method in Annex B of Eurocode-4 [34]. Therefore, Eurocode-4 was also referenced in this study, and the specimen width and length were set to 600 and 750 mm, respectively. The slab thickness was set to 220 mm, using the minimum slab thickness regulations presented in the South Korean concrete design standards (Ultimate Strength Design Method, [35]). For the shear specimen slab, a cast-in-place slab was used, and Figure 4 provides a diagram of the specimen design. A total of 18 specimens were fabricated, and the steel girder H beams were composed of SM490A grade steel with a 300(B) \(\times\) 300(H) \(\times\) 10(t\({}_{w}\)) \(\times\)15(t\({}_{f}\)) cross-section. The specimens were classified according to the type of shear connector, as shown in Figure 5 and Table 1. S1 had a conventional welded headed stud. S2 had a bolted shear connector in which a hexagonal nut was fastened in an embedded manner. For S3, a Y-shaped nut was fabricated instead of a hexagonal nut, and the upper flange of the steel girder was cut into a Y-shape so that there was a wedging effect when the embedded nut was fastened. Two modelswere considered, using cutting angles of 20\({}^{\circ}\) and 45\({}^{\circ}\). S4 had a shape similar to that of S3, but the Y-shaped nut was integrated into the stud bolt instead of using an embedded nut, and the two Y-shape angles were the same as the cutting angles, at 20\({}^{\circ}\) and 45\({}^{\circ}\). The shear connectors used in S1, S2, and S3 were conventional welded headed stud products composed of SS275 material. S4 used SM45C (non-heat-treated), which is a structural steel that is easy to cut and machine into threads. The shear connector of each specimen had a slab embedding length of 150 mm and diameter of 22 mm. Figure 6 shows the manufacturing process for the specimens. For the bolted shear connector specimens, drilling was performed at a diameter of 24 mm because 22 mm bolts \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Case**} & **Specimen** & **Slab Design** & **Stud Diameter** & **Stud Height** & **Y-Shape Angle** & \multirow{2}{*}{**Quantity**} \\  & **Name 1** & **Strength (MPa)** & **(mm)** & **(mm)** & **(Embedded Nut)** & \\ \hline S1 & S1-\#1-3 & 30 & 22 & 150 & - & 3 \\ S2 & S2-\#1-3 & 30 & 22 & 150 & - & 3 \\ S3–20 & S3–20-\#1-3 & 30 & 22 & 150 & 20 & 3 \\ S3–45 & S3–45-\#1-3 & 30 & 22 & 150 & 45 & 3 \\ S4–20 & S4–20-\#1-3 & 30 & 22 & 150 & 20 & 3 \\ S4–45 & S4–45-\#1-3 & 30 & 22 & 150 & 45 & 3 \\ \hline \hline \end{tabular} Note: 1 \(\#1\) and \(\#2\): Monotone increase (displacement control); \(\#3\): After 25 rounds of repeated loading, monotone increase (displacement control).  
\end{table} 
Table 1: Detail information for specimens and studs. Figure 4: Geometric details for push-out specimens: (**a**) section view; (**b**) side view. Figure 5: Shear connector shapes: (**a**) welding stud; (**b**) single-nut stud bolt; (**c**) tapered-nut stud bolt; (**d**) Y-shaped stud bolt. were used due to the machining standards of the steel girder hole. In cases 3 and 4, holes with a diameter of 24 mm were drilled to fasten the stud bolts to the upper flange of the steel girder. Then, a Y-shaped taper was machined in the upper part to match the set angle so that the tapered, inclined surface was completely in contact when the bolts were fastened. After the bolts and nuts were fastened, the bolted shear connector specimens were fabricated by placing the rebar, installing the formwork, placing the concrete, and curing the concrete.