## 3 Fatigue Test Results  
### Fatigue Failure Mode  
The failure details of the three specimens (S-1, S-2 and S-3) in the fatigue test are provided in Figure 6. The global failure pattern of all specimens was the fracture of headed shear studs without a large area crushing and cracking of the concrete slabs, leading to a separation between the concrete slab and the H-shaped steel column on one side (Figure 6a,d,g). As shown in Figure 6a, the bottom row shear studs (studs No. 2 and No. 8) \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Specimens**} & **Minimum Load** & **Maximum Load** & **Load Range \(\Delta P\)** & **Loss Range \(\Delta\tau\)** \\  & \(P_{\text{min}}\) (kN) & \(P_{\text{max}}\) (kN) & **(kN)** & **(MPa)** \\ \hline S-1 & 50 & 350 & 300 & 0.14 & 98.6 \\ S-2 & 40 & 400 & 360 & 0.10 & 118.4 \\ S-3 & 30 & 370 & 340 & 0.08 & 111.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Fatigue loading details for push-out specimens. Figure 5: Fatigue loading procedure. in the left concrete slab fractured when specimen S-1 failed. For stud No. 2 of specimen S-1, the failure mode of the stud was rather peculiar (Figure 6b). The fatigue crack originated from the root of the stud and propagated through the stud shank. However, the crack propagation range exceeded the stud shank to the base metal of the steel flange plate. The final tear damage did not appear along the crack tip, but approximately perpendicular to the crack surface on the most unfavorable section of the unbroken part of the stud. It indicated that stud No. 2 was suddenly broken due to the impact effect of the suddenly increased shear load when stud No. 8 was first damaged by the fatigue load. The fatigue failure mode of stud No. 8 of specimen S-1 had some similarities with that of stud No. 2, but there were obvious differences. Except for the fatigue fracture in the stud shank, the fatigue crack growth at the root of stud No. 8 also exceeded the range of the stud shank to the steel flange plate (Figure 6c) [18]. The crack initiation positions were opposite for the two fatigue damages of stud No. 8 in the vertical direction, one at the top of the stud shank and the other one at the bottom of the welding root. Under cyclic loading, the two fatigue damages of stud No. 8 had opposite crack propagation directions, as shown in Figure 6c. However, the final failure of stud No. 8 was due to the crack on the cross-section of the stud shank that was about one stud diameter away from the welding root. Moreover, the fractured surface of shear studs (studs No. 2 and No. 8) consisted of a smooth and a rough region. The smooth region was the fatigue crack initiation and propagation surface, while the rough region was the final rupture surface caused by a critical shear load. For specimen S-2, the bottom row studs (studs No. 4 and No. 6) in the right concrete slab fractured (Figure 6d), both of which shared the same local failure mode (Figure 6e,f). The fatigue crack started from the stud root, and propagated through the stud shank. After a certain number of fatigue loadings, the fatigue crack propagation caused a sufficient cross-section reduction in the stud and, finally, the two studs suffered the shear fracture. The global failure characteristics of specimen S-3 under cyclic loading were similar to that of specimen S-2, both of which were the fracture of studs No. 4 and No. 6 in the right concrete slab. The fractured surface of stud No. 6 (Figure 6i) at the root of the shear stud was consistent with that of the previous ruptured stud, i.e., including the fatigue and shear fracture part. However, there was a black stamp on the fracture surface of stud No. 4, which may be related to the welding defects (Figure 6h). The fracture surface of stud No. 4 was, thus, in the form of a shear fracture. In summary, there were two kinds of local failure modes observed for headed shear studs under cyclic loading: a fracture in the root of studs (stud No. 2 of specimen S-1, studs No. 4 and No.