# Ultimate Compressive Strength of H-Section Stub Columns Subject to Random Fitting Corrosion Damage
## 2 Numerical Modelling of H-Section Columns
### Randomly Pitted H-Section Columns
In natural corrosive environments, corrosion damage may occur on a structural component, being highly dependent on its specific service condition. The uncertainty of corrosion occurrence on the surface of a structural component is significant. Therefore, the compressive strength and behavior of H-section columns were studied, considering different corrosion patterns. They included four basic corrosion patterns, such as single-flange corrosion (SF), double-flange corrosion (symmetric, DF, and asymmetric, AF), web corrosion (W), and combined corrosion with both the flange and web corrosion, as shown in Figure 4. The term \"single-flange corrosion\" referred to a corrosion pattern where only one side of the flange near the web was pitted, as depicted in Figure 4a. \"Double-flange corrosion\"  
Figure 3: H-section analysis model: (**a**) distribution of pit depth; (**b**) distribution of pit diameter; (**c**) size parameters of H-section; and (**d**) H-section with random corrosion pits. indicated corrosion on both the upper and lower flanges, which can be further classified as symmetric or asymmetric. In the symmetric pattern, both the upper and lower flanges suffered from identical pitting corrosion in the degree of volume loss (\(DOV\)) and distribution of corrosion pits. In contrast, the asymmetric pattern shows different distributions of corrosion pits while maintaining the same \(DOV\), as illustrated in Figure 4b. Figure 4c exemplifies \"web corrosion\", which occurred on one side of the web. Based on the aforementioned corrosion patterns, combined corrosion occurred when flange and web corrosion coexisted. The combined corrosion pattern contained single-flange and web corrosion, known as \"single-flange combined corrosion\" (SF + W), as well as double-flange and web corrosion. In the latter case, symmetric and asymmetric combined corrosion were denoted as \"DF + W\" and \"AF + W,\" respectively. It is important to note that throughout the following study, unless explicitly stated otherwise, all numerical models strictly adhered to this nomenclature. As an example, \"H11.5 \(\times\) 7.5\(-\)DF + W\(-\)13.8%\" represented a randomly corroded H-section column with a flange thickness of 11.5 mm and a web thickness of 7.5 mm. The column was subject to combined corrosion on the flanges and web, with a symmetric corrosion pattern. Each plate element of the column had the same \(DOV\) of corroded material, specifically 13.8%. The H-section stub steel columns tested in reference [24] possessed the following dimensions: a length of 450 mm, a flange width (\(B\)) of 175 mm, a section height (\(H\)) of 175 mm, a flange thickness (\(t_{\textit{f}}\)) of 11.5 mm and a web thickness (\(t_{\textit{w}}\)) of 7.5 mm. These identical H-section sizes were adopted for the numerical models in this study. To mimic axial loading, the constraint condition of the numerical models was set as fixed end, in accordance with the experimental study, but one end of the numerical models was allowed to exert axial displacement. For numerical analyses, a bilinear ideal elastic-plastic model was utilized as the constitutive model for the steel. The material properties included an elastic modulus (\(E\)) of 196 GPa, [PERSON]'s ratio (\(\
u\)) of 0.3, yield strength (\(f_{\textit{y}}\)) of 390.09 MPa, and tensile strength (\(f_{\textit{u}}\)) of 626.05 MPa, which were all identical to the tested columns [24]. Both material and geometric nonlinearity were taken into account, while the influence of residual stress was disregarded. The initial deflection of the columns was determined based on the measured values of real H-sections [12]. The peak values of \(B\)/153 and \(h_{\textit{l}}\)/385 were applied to the flanges and web of the columns, respectively.