# Ultimate Compressive Strength of H-Section Stub Columns Subject to Random Fitting Corrosion Damage
## 3 Results and Analyses
### Compressive Behavior of Randomly Pitted Columns
#### 3.1.3 Failure Mode  
The failure modes of randomly pitted H-section columns were investigated under two corrosion patterns: double-flange corrosion and double-flange combined corrosion. Figure 10 depicts the typical failure modes observed in both intact and corroded columns, along with the Von Mises stress contour. For clarity, column deformations in this figure are amplified by a factor of 5. The parameter \"\(l_{ver}\)\" represents the distance from the vertex of a buckling half-wave to the bottom of the column, and \"\(L\)\" denotes the length of the buckling half-wave.  
The findings from Figure 10 reveal a significant impact of random pitting corrosion on the failure behavior and stress distribution of H-section columns. In the ultimate state, local buckling occurred on both flanges of the columns. This was characterized by the presence of buckling half-waves along the length and width of the columns, with the outstand flange deforming outward or concaving inward along the column width. When comparing the intact column in Figure 10a to those affected by random pitting corrosion in Figure 10b, a more pronounced deformation resulting from local buckling was evident. Table 1 provides details concerning the length and location of buckling half-waves along the column length at the ultimate state, considering two corrosion patterns and varying levels of pitting intensities. Herein \"\(l_{min}\)\" represents the distance from the minimum cross-sectional area to the bottom of the column. It is worth noting that the length and position  
Figure 9: Axial stiffness under various corrosion patterns: (**a**) flange or web corrosion; (**b**) combined corrosion.  
of the buckling half-wave did not exhibit clear regularity. This differed from that observed in the H-section columns with general corrosion, where the half-wavelength decreases with the increase in corrosion intensity [12]. For instance, in the case of double-flange corrosion (H11.5 \(\times\) 7.5\(-\)DF), the half-wavelength (\(l\)) was 261 mm at a \(DOV\) of 4.8, being less than that (\(l\) = 266 mm) at the higher \(DOV\) of 13.8%. Moreover, the local buckling did not necessarily emerge on the minimum cross-section denoted by \(l_{min}\) = 38 mm but occurred on the cross-section at \(l_{var}\) = 269 mm. This can be attributed to the uncertainty associated with random pitting corrosion, which leads to irregular cross-sections throughout the column length. Consequently, rather than the weakest section of the column, the relatively weaker section, which was affected by random pitting damage, may prompt the local buckling of the column flanges, as shown in Figure 10b.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**No.** & \(DOV\) (\%) & \(l_{min}\) (mm) & \(l_{var}\) (mm) & \(l\) (mm) \\ \hline H11.5 \(\times\) 7.5 & 0 & — & 270 & 276 \\  & 4.8 & 224 & 228 & 261 \\  & 6.8 & 283 & 288 & 287 \\ H11.5 \(\times\) 7.5\(-\)DF & 8.8 & 280 & 288 & 340 \\  & 11.8 & 263 & 270 & 319 \\  & 13.8 & 38 & 269 & 266 \\  & 4.8 & 313 & 220 & 261 \\  & 6.8 & 283 & 288 & 319 \\ H11.5 \(\times\) 7.5\(-\)DF + W & 8.8 & 278 & 294 & 293 \\  & 11.8 & 161 & 270 & 298 \\  & 13.8 & 269 & 270 & 272 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Location and length of half-wave of intact and randomly pitted columns.  
Figure 10: Failure modes of intact and randomly pitted columns (stress contour unit: MPa): (a) intact column; (b) column at \(DOV\) 13.8%.