## 3 Push-Out Tests and Analysis of Results
### Experimental Results and Analysis  
Figure 10 presents the static experiment results for each of the experimental cases, and Tables 2 and 3 compare the overall experimental results. The load-slip displacement curve for each experiment case is the displacement curve of the LVDTIs installed in the specimens to measure the relative slip between the steel girders and concrete slab and the UTM load rather than the load-displacement values of the UTM. The stiffnesses of the repeated load parts of specimen #3 of models S1-S3 exhibit low consistency, unlike that of specimen #3 of model S4, because the values from the two displacement gauges installed at the front and back of the specimens were averaged, and it was confirmed that the repeated loading by the UTM was controlled normally like it was for S4. In the case of model S4, the step-wise decrease in strength at the ultimate load was caused by the fracturing of the shear connector bolt. Figure 8: Loading process [21]. Figure 9: Sensor locations: (**a**) LVDT and stud strain gauge installation; (**b**) concrete strain gauge installation. Figure 10: Load–slip relationship curves: (**a**) S1 (welding stud); (**b**) S2 (single-nut stud bolt); (**c**) S3-20 (tapered-nut stud bolt, 20\({}^{\circ}\)); (**d**) S3-45 (tapered-nut stud bolt, 45\({}^{\circ}\)); (**e**) S4-20 (Y-shaped stud bolt, 20\({}^{\circ}\)); (**f**) S4-45 (Y-shaped stud bolt, 45\({}^{\circ}\)); (**g**) all models. In the experiment results in Table 2, the ultimate strengths of all models except for S4-45 are lower than that of the conventional welded studs (S1). In particular, for the single-nut method, in which fastening is performed with an embedded hexagonal nut and which has been the main demounting method used, the ultimate strength is only 47.8%. The double-nut method was not investigated in this study, but due to the nature of the conventional nut method, the stud bolt thread is present in the nut contact surface with the upper flange, and consequently, the shear strength is greatly lowered due to the reduction in cross-section. Particularly in the case of S2, more initial slip occurred than in the other models, which seems to have caused significant reduction in not only the stiffness, but also the ultimate strength. On the contrary, unlike the embedded nut models (S1 and S2), the integrated Y-shaped stud bolt model (S4) has a higher ultimate strength equal to 93.9% of the ultimate strength of model S1 at a wedge angle of 20\({}^{\circ}\) and 104.6% at a wedge angle of 45\({}^{\circ}\). Model S4-45 shows a level of performance similar to that of S1 in terms of stiffness in the elastic interval before yielding. The other models have lower stiffnesses than model S1, but model S4-45 displays sufficient stiffness through integrated behavior similar to that of model S1 because not only was there no reduction in the stud shear surface due to the use of an integrated Y-shape rather than an embedded nut, but also the initial slip was blocked due to the wedging effect that occurred when the bolt was fastened because of its 45\({}^{\circ}\) angle. However, model S4-45 shows a maximum slip displacement equal to 65.4% of the maximum slip displacement of model S1. In addition, looking at the failure mode, tensile fracturing occurred in the fastening part of the stud bolt (the interface between the steel girder lower flange and nut) rather than shear fracturing at the embedded position of the stud (the interface between the upper flange of the steel girder and concrete slab). Of course, an average maximum slip displacement of 8.76 mm satisfies the relevant standards