## 6 Discussion  
In order to compare the capacity of different uprights, the average value of normalized ultimate loads was determined according to the test results. Figure 16 shows the normalized ultimate load capacity of uprights for both 1.6 mm and 2.5 mm thicknesses. The values of normalized ultimate loads are grouped by upright length and the type of reinforcement (bolt at 200 mm and 400 mm). As indicated in this figure, the ultimate load capacity improvement due to the reinforcement of the uprights, with different thickness and reinforcement, is decreased by increasing the upright length. This can be justified by this fact that at higher length the dominant buckling mode is flexural buckling failure mode which is not much affected by the proposed reinforcement method; therefore, increasing the ultimate capacity of the upright at higher lengths could not be achieved considerably. Figure 16 also indicates that employing bolt and spacer at 200 and 400 mm provides higher ultimate capacity compared to uprights without bolt and spacer which represents the capability of the proposed simple reinforcement method for increasing the load-bearing capacity of uprights. The effect of reinforcement spacing on the ultimate load capacity of uprights is also illustrated in Figure 17. As shown in this figure, a significant difference in the increase of the ultimate load capacity is observed for specimens 1800L-1.6T and 1800L-2.5T with reinforcement spacing of 200 mm compared to the 400 mm. For 1800L-1.6T upright, 33% and 12% increase in ultimate capacity resulted by employing bolts at 200 mm and 400 mm, respectively. A similar trend was also observed for 1800L-2.5T upright with 37% and 20% increase in ultimate capacity by employing bolts at 200 mm and 400 mm, respectively. Figure 16: Comparison of normalized ultimate load capacity. Figure 17: Effect of reinforcement by increasing the upright height. As shown in Figure 17, the effect of employing bolt and spacer in uprights ultimate capacity is decreased by increasing the upright height. Comparing 1800L-1.6T and 3600L-1.6T specimens show that the difference between the increase in load capacity of two types of reinforcement (bolt at 400 mm and 200 mm) decreases from 23% for 1800 mm upright to 10% for 3600 mm upright. The same behavior was also captured for 2.5 mm thickness upright (1800L-2.5T and 3600L-2.5T) showing that the difference between the increased ultimate loads for the two types of reinforcement is 17% and 5% for 1800 mm and 3600 mm uprights, respectively. This indicates that the application of bolt reinforcement in shorter pitches (200 mm) in longer uprights does not offer extra resistance as much as it provides for shorter uprights since the failure of longer uprights is dominated by flexural buckling mode. Therefore, it can be concluded that although reducing the spacing of the bolts and spacers can improve the distorsional buckling capacity considerably; as discussed earlier, the effect of the reinforcement spacing on buckling mode change for higher lengths uprights is not considerable. Figure 18 shows the effect of section thickness on the results of reinforced uprights. As shown in this figure, the reinforcement in 2.5 mm thick upright could increase the ultimate load capacity of upright much more than reinforcement in uprights with 1.6 mm thickness. A similar trend was observed in both types of uprights with 200 mm and 400 mm bolt and spacer; however, the difference between increased ultimate load for specimens with 200P is less than the difference between increased ultimate loads for specimens with 400P, for both thicknesses. In other words, when uprights were reinforced with bolts at 200 mm, the increased ultimate load percentage for 2.5 mm upright was closer to the increased ultimate load for upright with 1.6 mm compared to the other type of reinforcement (at 400 mm)  
For the 1800L-1.6T-400P and 1800L-2.5T-400P uprights, the increased ultimate load capacity was 10% and 20%, respectively.