# Experiment on Flexural Fatigue Performance of Precast Bridge Deck Joints with Loop Connections
## 3 Experimental Design
### Test Setup
#### 3.2.2 Arrangement of Measurement System  
In order to obtain the strain distribution of the steel bar and concrete under the fatigue load, strain gauges are arranged on the surface of the steel bar and concrete.  
The strain measuring points of the steel bar can be mainly divided into three categories as follows:  
1. Strain measuring points of the longitudinal loop bar in the joint segment: The measuring points are arranged near the junction of the straight-line section and the curve section of the loop bar. The distance between the measuring point and the end of the loop bar is about 85 mm. Due to the form of double overlaps adopted by the specimen SF3, measuring points are also arranged at the symmetrical center of the longitudinal loop bars in the joint segment.
2. Strain measuring points of longitudinal loop bar on both sides of the interface: the measuring points are arranged at the position of 50 mm on both sides of the interface between joint segment and precast segment.
3. Strain measuring points of transverse steel bar: The measuring points are arranged at the appropriate position of the transverse steel bar. The spacing between measuring points of the specimen SF1 is 300 mm and that of the specimens SF2 and SF3 is 200 mm.  
The strain measuring points of concrete are mainly arranged on the upper surface, lower surface, and side of the specimen:  
Figure 4: Loading path for flexural fatigue test (specimen SF1 for instance).  
1. Concrete measuring points on the upper surface: Four concrete strain measuring points are arranged along the center line of the specimen. The spacing between the measuring points of specimen SF1 is 150 mm, and that of specimens SF2 and SF3 is 100 mm.
2. Concrete measuring points on the lower surface: Four concrete strain measuring points are also arranged along the center line of the specimen. In addition, four concrete strain measuring points are arranged at the interface between the joint section and the prefabricated sections on both sides. The total number of concrete strain measuring points on the lower surface is 12. The spacing between the measuring points of specimen SF1 is also 150 mm, and that of specimens SF2 and SF3 is 100 mm as well.
3. Concrete measuring points on the side of the specimen: Along the center line of the specimen and the action line of fatigue load, three measuring points are arranged at different heights on the side of the specimen. A total of six measuring points are arranged in each specimen.  
In addition, the displacement meter is also arranged to measure the displacement change of the pure flexural segment under the fatigue load. A total of six measuring points are arranged on both sides of each specimen. For one side of the specimens, one measuring point is located at the center line of the specimen, and the other two measuring points are located at the position of the loading action line.  
Taking the specimen SF1 as an example, the arrangement of the measuring points is presented in Figure 5.  
Figure 5: Arrangement of measurement system: (**a**) strain measuring point of concrete; (**b**) laser displacement sensor; and (**c**) strain measuring points of steel bar.