## 5 Results  
Compression tests were performed on the upright frames with two different thicknesses and five types of lengths, and the effect of reinforcement at 400 mm and 200 mm was investigated. Ultimate load capacities, as well as failure modes, were recorded from the compression tests and the results were accurately analyzed. At the end of the test, failure modes were investigated based on the experimental observations. For some specimens, it was relatively difficult to detect which mode of failure is dominant since the interaction of two or three buckling modes had occurred. Figure 11: Preliminary elastic buckling analyses for the individual un-perforated upright gross sections (stress values have not been disclosed due to confidentiality). The ultimate load capacity of each test was extracted and normalized with respect to the gross cross-section (A\({}_{\text{g}}\)) and the mean yielding strength (\(\sigma_{\text{y}}\)) due to the confidentiality matters. The normalized load-displacement curves of the specimens with 2.5 mm thickness are shown in Figure 12. The normalized load value is related to the compressive load applied on top of the upright, while the displacement value shows the deformation of the top head of the upright measured by LVDT. For each specimen type, at least three tests were carried out as recommended by the Australian Racking code (AS4084: 2012) [33]. The reason for the different ultimate values for these three tests of each specimen can be attributed to the fact that upright elements have different initial geometrical imperfections associated with the manufacturing processes [34]. The normalized ultimate load capacity of each test, average value, and standard deviation for each specimen are provided in Table 3. In general, three types of failure modes were observed in the experimental tests: (a) Distortional buckling failure which was dominant for specimens with 1800 mm length; (b) flexural or torsional mode or combination of them was also dominant for specimens with 3000 mm and 3600 mm length; and (c) transition from distortional buckling to flexural buckling failure which happened for specimens with 2400 mm length. Local buckling was also observed in some  
Figure 12: Load displacement curves for 2.5 mm thick specimens. Figure 13: _Cont._  
According to Figure 13, the buckling mode of specimens with 3600 mm and 3000 mm, was hardly affected by employing bolts and spacers at either 200 mm or 400 mm. Therefore, it was concluded that the load capacity for specimens with and without reinforcement at higher length is not affected as significantly as shorter specimens. This is mainly because the buckling mode of failure in high length upright is governed by flexural and torsional flexural buckling, and utilizing reinforcement strategy does not necessarily change or control the buckling mode. It can be noted that one of the most effective parameters that determine the failure mode of the uprights under compression is the upright height and reinforcement might not overcome this issue. Interestingly, for the short specimens with 1800 mm and 2400 mm length, the reinforcement system was extremely effective. Distortional buckling was the primary failure mode for these specimens and utilizing reinforcement could shorten the half-wavelength of the specimen resulting in capturing higher capacity when 400 mm and 200 mm bolts were used. The failure of the short specimens was primarily dominated by distortional buckling of the flange; while, for the taller uprights the elements were vulnerable to flexural-torsional buckling at mid-span where the uprights had low rigidity. The effect of section thickness on the performance of an upright is considerable and should be investigated through experimental tests. Hereinto, the uprights with lower thickness were also experimentally tested in order to have a better comparison with thicker uprights. The normalized load-displacement curves of specimens with 1.6 mm thickness and their failure modes are shown in Figures 14 and 15.