## 3 Experimentation Results  
### Reinforcement Performance of Steel Fiber-Reinforced Concrete  
(1) Concrete strain at the variable cross-section  
The strain was measured by installing strain gauges at the umbrella arch location under an external load of 1000 KN; the concrete in the 1/3 and 2/3 prefabricated crack components strengthened by the umbrella arch exhibited maximum compressive strains of \(-1021\)\(\mu\epsilon\) and \(-1431\)\(\mu\epsilon\), respectively. Under this loading condition, the maximum compressive strain in the concrete at the variable cross-section met the design specifications and did not result in crushing.  
(2) Surface concrete strain near prefabricated cracks  
The strain was measured using strain gauges positioned near the prefabricated cracks. After collecting and analyzing the test data, the maximum compressive strains of concrete near the prefabricated cracks amounted to \(-605\)\(\mu\epsilon\) and \(-852\)\(\mu\epsilon\) for the 1/3 and 2/3 prefabricated crack components, respectively, reinforced by the umbrella arch under an external load of 500 KN. Under an external load of 1000 KN, the maximum compressive strains of the concrete near the prefabricated cracks were \(-1256\)\(\mu\epsilon\) and \(-1752\)\(\mu\epsilon\) for the 1/3 and 2/3 prefabricated crack components, respectively, reinforced by the umbrella arch. Under this load, the maximum compressive strain of the surface concrete near the prefabricated cracks met the design specifications and did not result in any crushing.  
Figure 4: Specim loading.  
Figure 3: Schematic diagram of strain gauge and dial gauge positions.  
(3) Distortion  
As shown in Figure 5a, components 1, 2, and 3 exhibit brittle failure under load, and the rate of change in mid-span distortion increases progressively with increasing load. Under the same load, mid-span distortion increases as the degree of cracking increases; components 4 and 5 exhibit relatively minor mid-span distortions before damage as the load increases. Component 1 fails under a load of 700 KN, components 2 and 3 fail at 550 KN, and components 4 and 5 do not fail even under a load of 1000 KN. The mid-span distortions for components 1, 2, 3, 4, and 5 under the respective loads measure 5.01 mm, 4.78 mm, 6.31 mm, 3.25 mm, and 3.57 mm, respectively.  
As depicted in Figure 5b, as the load increases, there is a general decrease in the bending stiffness of the components. For component 4, stiffness decreases sharply between 0 and 200 KN, and cracking occurs along the prefabricated lines. Stiffness remains relatively stable between 200 and 600 KN, during which the original lining and the umbrella arch are co-stressed, resulting in cracks within the umbrella arch. Between 600 and 1000 KN, the original lining nears destruction. Concurrently, the umbrella arch, now bearing the load independently, shows further stiffness reduction, more extensive cracking, and transition of the component into a plastic state. For component 5, stiffness decreases sharply between 0 and 150 KN, with cracking along the prefabricated lines. Between 150 and 500 KN, stiffness is relatively stable with a slight upward trend; the force on the original lining decreases while that on the umbrella arch increases, leading to further cracking. Between 500 and 1000 KN, the load-bearing capacity of the arch decreases significantly, prompting the components to transition to a plastic state and commence degradation. Under load, the stiffness of components 1, 2, and 3 decreases markedly, exhibiting brittle failure.