## 2 Experimental Analysis of the Bearing Capacity of the Horizontal Bar
### Bending Performance of the Horizontal Bar
#### 2.2.2 Experimental Results and Analysis  
At the beginning of the experimental loading, there was almost no bending deformation of the horizontal bar specimen. When the load increased, the bending deformation began at the midspan of the specimen, but it was relatively slow. As the load continued to increase, the speed of bending deformation of the specimen increased, and the vertical displacement obviously increased obviously. When the midspan vertical displacement of the specimen increased continuously, and the flexural bearing capacity did not change significantly, loading was stopped. At the end of the experiment, observations of the morphology of bending failure of the horizontal bar (Figure 9) showed that plastic bending deformation occurred in the midspan of the specimen and the sockets at both ends were not damaged. There were no cracks in the tube wall of the specimen and the weld seam at the connection between the socket and the horizontal bar. The experimental data for the flexural bearing capacity of the horizontal bar are shown in Figure 10. The vertical deformation of the specimen increased linearly from the initial loading stage to when the flexural bearing capacity reached 9 kN\(\cdot\)m. Then, as the bearing capacity increased from 9 kN\(\cdot\)m to the ultimate bearing capacity of 10.95 kN\(\cdot\)m, the vertical displacement of the midspan increased faster. When the horizontal bar reached its ultimate bending capacity, bending yield occurred in the midspan of the specimen, and local plastic instability occurred as well. This resulted in a continuous decrease in the flexural bearing capacity of the horizontal bar and the continued rapid increase in the vertical displacement of the midspan.  
According to the experimental behaviour of the horizontal bar and the force analysis of the horizontal bar, three main reasons affected the failure of the horizontal bar: (1) shear failure of the socket, (2) damage of the weld node between the socket and the horizontal bar by tension (compression), and (3) bending failure of the horizontal bar. The theoretical calculation formula was as follows:  
When the socket is sheared,  
\[F^{\prime}=f_{v}^{w}\cdot A^{\prime} \tag{3}\]  
Figure 8: Experimental device for measuring the bending capacity of a horizontal bar.  
Figure 9: Bending failure mode of a horizontal bar.  
When the welding seam at the connection between the socket and the horizontal bar is under tension (compression),  
\[F^{\prime\prime}=\sum l_{w}\cdot h_{\epsilon}\cdot f_{c}^{w} \tag{4}\]  
When the horizontal bar is bent,  
\[F^{\prime\prime}=\frac{N}{A}+\frac{M}{W} \tag{5}\]  
From the above experimental conclusions and results of the theoretical calculations, it was clear that the weld bearing capacity at the connection between the socket and the horizontal bar was the lowest among the three influencing factors. Therefore, the welding seam at the connection between the socket and the horizontal bar was the weak point of the bearing capacity of the horizontal bar of the formwork support. In practical engineering, the control of weld quality at the node of a horizontal bar and socket is key to ensuring the bearing capacity of a horizontal bar and plays a vital role in ensuring the safe use of the formwork support.