# Bending Behavior of Corroded H-Shaped Steel Beam in Underground Environment
## 2 Experimental Setup
### Corrosion Scheme  
An investigation of various coal mining enterprises in the Shandong province of China was conducted by the author. It was found that the H-shaped steel beams used for tunnel support are not coated with anticorrosive paint to reduce the cost. Therefore, in this study, the tensile samples and steel beams were not subjected to anti-corrosive treatment. Three tensile samples were not corroded and were used for comparison. Another nine tensile samples were divided into three groups (Group I, Group II, Group III; see Table 1) according to the corrosion period of 60 days, 120 days, and 180 days, and each group included three tensile samples. The naming format for the tensile samples is \"T-corrosion period-number\". Among the 10 H-shaped steel beams, one beam was not corroded and was used for comparison. The remaining nine beams were divided into groups A, B, and C according to the corrosion periods, and each group included three beams. The period was 60 days, 120 days, and 180 days for groups A, B, and C, respectively. To simulate the actual corrosion, the samples in each group were corroded under a sustained load of 0, 0.3, and 0.6 times the yield load \(F_{y}\) of the steel beam, respectively, using the four-point bend loading method, as shown in Figure 3. With regard to naming, each corroded sample was named according to \begin{table}
\begin{tabular}{c c c} \hline \hline
**Group** & **No.** & **Corrosion Time/d** \\ \hline \multirow{2}{*}{Ref. specimen} & T-0-1 & 0 \\  & T-0-2 & 0 \\  & T-0-3 & 0 \\ \hline \multirow{2}{*}{Group I} & T-60-1 & 60 \\  & T-60-2 & 60 \\  & T-60-3 & 60 \\ \hline \multirow{2}{*}{Group II} & T-120-1 & 120 \\  & T-120-2 & 120 \\  & T-120-3 & 120 \\ \hline \multirow{2}{*}{Group III} & T-180-1 & 180 \\  & T-180-2 & 180 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Tensile sample grouping. Figure 2: Schematic diagram of test beam size (unit: mm). its group number, corrosion period, and loading ratio. For example, GB-120-6 means that a beam in group B was corroded under a load of 0.6 \(F_{y}\) for 120 days. Specific information for each group is provided in Table 2.  
Replicating the underground coal mining environment in the laboratory is difficult. By considering that the temperature and corrosive liquid are key factors leading to the corrosion of steel, a custom-made corrosion environment simulation system was established in the laboratory and consisted of a temperature control system and a spraying system. The temperature control system was capable of adjusting and maintaining the environmental temperature within a certain range. The spraying system operated on a timer and the amount of spraying could also be adjusted. The field investigation of a coal mining tunnel environment in Shandong Province revealed that the average temperature at the site reaches 35 \({}^{\circ}\)C and the concentration of SO4\({}^{2+}\) in the field water sample was the highest, reaching 4729 mg/L. Therefore, the temperature of the custom-made corrosion environment simulation system was controlled at 35 \({}^{\circ}\)C. The used solution was sodium sulfate (Na2 SO4) with a mass fraction of 10% and was sprayed twice daily. The amount of 0.0124 m\({}^{3}\) was sprayed every minute for two minutes each time. Both the tensile samples and H-shaped steel beams were corroded in this environment simulated system. It was verified that the sprayed amount could uniformly wet the surface of the test samples. The relative humidity was monitored by two hygrometers, and the relative humidity value was between 80 and 95% during the corrosive process.