# Bending Behavior of Corroded H-Shaped Steel Beam in Underground Environment
## 5 Discussion  
The degree of corrosion of steel is usually characterized by mass loss rate [16], volume loss rate [18], area loss rate [31] or thickness loss rate [32]. These three characterization parameters are equivalent and can be converted from each other. Regression analysis is the common method to analyze the relationship between yield strength or ultimate strength of corroded steel and corrosion degree. Almost all studies show that the mechanical properties of corroded steel are degraded with the increase in corrosion degree. However, the degradation rules are different. For example, [PERSON] et al. [16] studied the mechanical properties of steel corroded in acid environment and found that the yield strength and ultimate strength of corroded steel decreased linearly with the increase in mass loss rate. [PERSON] et al. [18] studied the mechanical properties of steel corroded in a marine environment. The results show that the yield strength and ultimate strength of corroded steel decrease nonlinearly with the increase in volume loss rate (quadratic polynomial relationship). [PERSON] et al. [32] studied the mechanical properties of steel corroded in atmospheric environment. The results show that the yield strength and ultimate strength of corroded steel decrease linearly with the increase in thickness loss rate. The main reason for different degradation rules can be attributed to different corrosion environments, which lead to different corrosion morphologies. However, the research on the mechanical properties of corroded steel rarely involves the underground environment of a coal mine. This paper investigated the mechanical properties of steel corroded in coal mine environment and found that the yield strength and ultimate strength of corroded steel decrease nonlinearly with the increase in mass loss rate. In addition, this paper found that the steel underwent uniform corrosion and uneven corrosion simultaneously in the underground environment of coal mine. However, this paper did not measure uniform corrosion and non-uniform corrosion separately, because of the limitation of the test conditions. In future, the effect of the uniform corrosion and uneven corrosion on the mechanical properties of corroded steel should be studied further.  
The research on the mechanical properties of corroded steel members shows that the bearing capacity of steel members decreases with the increase in corrosion rate [16; 18]. This is mainly due to the change of material properties and section size. In addition, local corrosion is also the key factor affecting the mechanical properties of corroded steel mem  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Specimens** & **P\({}_{y}\)/kN** & **P\({}_{u}\)/kN** & **P\({}_{ye}\)/kN** & **P\({}_{ue}\)/kN** & **P\({}_{y}\)/P\({}_{ye}\)** & **P\({}_{u}\)/P\({}_{ue}\)** \\ \hline GA-60-0 & 197.09 & 261.61 & 191.35 & 238.50 & 1.03 & 1.10 \\ GA-60-3 & 195.31 & 254.75 & 184.52 & 230.01 & 1.06 & 1.11 \\ GA-60-6 & 184.56 & 237.26 & 178.34 & 222.31 & 1.03 & 1.07 \\ GB-120-0 & 186.83 & 248.00 & 165.88 & 206.82 & 1.13 & 1.20 \\ GB-120-3 & 184.39 & 237.77 & 161.34 & 201.17 & 1.14 & 1.18 \\ GB-120-6 & 176.22 & 225.45 & 159.24 & 198.56 & 1.11 & 1.14 \\ GC-180-0 & 178.38 & 237.23 & 154.76 & 192.99 & 1.15 & 1.23 \\ GC-180-3 & 170.17 & 230.32 & 154.41 & 192.56 & 1.10 & 1.20 \\ GC-180-6 & 162.57 & 217.99 & 152.15 & 189.75 & 1.07 & 1.15 \\ \hline \hline \end{tabular} Notes: P\({}_{y}\) is the measured yield load of a corroded steel beam; P\({}_{u}\) is the measured ultimate load of a corroded steel beam; P\({}_{ye}\) is the yield load of a corroded steel beam; P\({}_{ue}\) is the ultimate load of a corroded steel beam.  
\end{table}
Table 7: Measured value and calculated value.  
bers [25; 26]. However, this paper only studies the global corrosion of H-beam, the residual bearing capacity prediction method only considers the change of material properties and section size. The local corrosion needs to be further explored.