# Experiment on Flexural Fatigue Performance of Precast Bridge Deck Joints with Loop Connections
## 3 Experimental Design
### Test Setup  
#### 3.2.1 Loading Setup  
The flexural fatigue specimens SF1 to SF3 are tested with an electro-hydraulic pulsating fatigue testing machine (PMW800-500). The maximum test force of the testing machine is 500 kN, and the maximum pulsation value is 800 mL/time.  
In the flexural fatigue test, the four-point flexural loading method is applied. The distance from each support to the end of the specimen is 150 mm. And the loading points are arranged at a distance of 550 mm from the support. The vertical load is transmitted to the steel blocks at the position of the loading points through the distribution beam, and a pure flexural segment is formed in the middle of the specimen. The arrangement of the test device is shown in Figure 3.  
Similarly, the static test of the specimen B3-A is also carried out using the four-point flexural loading method. In the static loading test, the distance between the support and the loading point is the same as that of the flexural fatigue test.  
According to the relevant regulations of the Chinese standard JTG 3362-2018 [25] 'Specifications for Design of Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts', the peak value of fatigue load for the flexural fatigue test is determined.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Dimension**} & \multicolumn{3}{c}{**Joint Size**} & \multicolumn{3}{c}{**Layout of Loop Connections**} \\ \cline{3-8}  & & **Thickness** & **Width** & \begin{tabular}{c} **Transverse** \\ **Spacing** \\ \end{tabular} & \
\begin{tabular}{c} **Bar Diameter** \\ **Length** \\ \end{tabular} &
\begin{tabular}{c} **Overlapping** \\ **Form** \\ \end{tabular} \\ \hline B3-A & 2050 \(\times\) 720 \(\times\) 220 & 220 & 250 & 75 & 20 & 180 & Single \\ SF1 & 2050 \(\times\) 720 \(\times\) 220 & 220 & 250 & 75 & 20 & 180 & Single \\ SF2 & 2300 \(\times\) 520 \(\times\) 160 & 160 & 500 & 50 & 16 & 200 & Single \\ SF3 & 2500 \(\times\) 520 \(\times\) 180 & 180 & 700 & 50 & 16 & 200 & Double \\ \hline \hline \end{tabular}
\end{table}
Table 1: Design parameters of specimens (Unit: mm).  
Figure 3: Load setup for flexural fatigue tests: (**a**) front view and (**b**) lateral view.  
According to the relevant calculation, when the live load level is in the Highway Grade I, the flexural moment of the mid-span section caused by the live load in unit length is about 30 kN-m. In order to make the applied fatigue load reach the loading effect of the maximum flexural moment, the peak fatigue load of specimen SF1 is about 40 kN, and that of specimens SF2 and SF3 is about 30 kN. The valley value of fatigue load is taken as 40% of the peak value, which is 16 kN and 12 kN, respectively.  
Before the fatigue test, the specimens are preloaded. In a preloading process, the specimen should be first loaded to 5 kN, and then unloaded to 0 kN. This preload process should be repeated three times.  
After \(0\times 10^{4}\) (i.e., before the fatigue loading), \(5\times 10^{4}\), \(10\times 10^{4}\), \(30\times 10^{4}\), \(50\times 10^{4}\), \(100\times 10^{4}\), and \(200\times 10^{4}\) fatigue-loading cycles, the fatigue test should be suspended, and the specimens will be subjected to static loading. During the static loading process, the specimens are loaded to the upper limit of fatigue by stages, and various parameters of the specimens are observed. Actual loading path for flexural fatigue test is demonstrated as Figure 4.