## 3 Experimental Investigation  
The testing programme comprised 21 channels, tested using a Universal Instron Testing Machine. The tested channel sections had various web heights ranging from 100 mm to 250 mm, where the depth of the flat portion of the web over web thickness (h/t) ranged from 60.9 to 82.6 in the experimental programme. Considering the guideline of AISI S100 [31], the length of tested channels (L) was threefold the web height plus the length of the top bearing plate. The channels were tested as a single web channel, where the details and dimensions measured in the lab have been presented in Table 1. Nomenclature of the tested channels is shown in the Figure 1a. For simplicity in identifying the test channels, specimen labelling comprised of the channel thickness, dimensions, and top loading plate length. The channel labelled as \"200\(\times\)75-3.0-N50\" is clarified as follows. The first part of the labelling as \"200 \(\times\) 75\" implies the nominal height of the channel and flange width in units of millimetres, while \"t3.0\" indicates the thickness of the web being equal to 3.0 mm. The annotation \"N\" denotes the length of the top load-bearing plate. As shown in Figure 1b, the channel specimens were tested subject to concentrated transverse localised force, namely Interior Loading (IL). The channels were tested considering AISI S100 [31]. The vertical force is applied to the mid-length of channels on top channel flanges using a high-strength steel plate. Steel half rounds were placed on top of the steel loading plate at mid-length of the channel specimen considering vertical alignment with line of forces. Using the Instron Universal Testing Machine, a linear constant load with a load rate of 0.5 mm/min was applied. The testing configuration for channel specimens subject to Interior Loading (IL) is shown in Figure 1b. A series of 9 tensile coupon tests were conducted to determine the mechanical properties of the channel specimens. Figure 2  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Channel**} & **Plate Length** & **Web** & **Flange** & **Web** & **Fillet** & **Channel** & **Experimental** \\  & **N** & **d** & **b\({}_{t}\)** & **t** & **r** & **L** & **FExp** \\  & **(mm)** & **(mm)** & **(mm)** & **(mm)** & **(mm)** & **(mm)** & **(km)** \\ \hline C100\(\times\)50-15.0-N50 & 50 &  
shows the tensile coupon test set-up and stress-strain curve for channels with 3 mm thickness fabricated with G304L stainless steel, while Table 2 provides the material properties of the tested tensile coupons. The corresponding hot-rolled steel mechanical properties are found in [PERSON] et al. [32]. As previously mentioned, the testing programme comprised of a series of 21 channels with different channel sizes and thicknesses subjected to localised interior bearing loading. The experimental ultimate bearing capacities for single web channels, denoted as F\({}_{\text{EXP}}\), are given in Table 1. The typical mode of failures for the tested are depicted in Figure 3a,b. The laboratory test results are given in Table 1. Load-displacement curves obtained from tested channels labelled as C100\(\times\)50-t1.50-N100, C150\(\times\)60-t2.0-N100, C200\(\times\)75-t3.0-N75, and C250\(\times\)75-t3.0-N50 under Localised Interior Loading are shown in Figure 4 to provide more information. Figure 1: Stainless steel channels test. (**a**) Symbols definition; (**b**) Testing set-up for channels under IL loading condition. Figure 2: Tensile coupon test [11]. Figure 4: \(Cont.\)