Issue 78

S. M. Khalil et alii, Fracture and Structural Integrity, 78 (2026) 346-366; DOI: 10.3221/IGF-ESIS.78.20

the figure for t s = 8 mm (compact), the normalized load is around 3.3 for t w = 4 mm, and reduced to 2.2 for t w = 8 mm. The same is noticed for ts = 4 mm (non-compact), where the normalized load is around 2.5 for t w = 4 mm, and reduced to 1.5 for t w = 8 mm. For t s = 2 mm (slender), the observation is less pronounced because of the weakness of the stiffener to strengthen the web, as discussed in the last section. To conclude, a ratio between the stiffener and web thickness is presented in Fig. 15, showing the relationship between the normalized load and the ratio t s /t w . A ratio of 1.0 is recommended, where the gain ratio for different models is found to be above 100% (normalized load above 2.0). For ratios t s /t w larger than unity, models with large web thickness and loaded length show constant gain. Any additional increase in the stiffener thickness does not affect the gain, while some increase is noticed when a small web thickness and a small load length are used. For ratios t s /t w smaller than unity, the strength gain goes down rapidly. As a conclusion, it can be recommended to use a stiffener with a thickness equal to the web thickness, keeping in mind the compactness recommendation of the stiffener plate.

Figure 12: Normalized load versus stiffener thickness for models with h w = 500 mm and different t w .

Figure 13: Normalized load versus stiffener slenderness ratio for models with h w = 500 mm and different t w .

Figure 14: Normalized load versus web thickness for models with h w = 500 mm and different W and ts.

Figure 15: Normalized load versus ts/tw ratio for models with h w = 500 mm and different W and t w .

Effect of loaded length (W) Increasing loaded length guarantees a wider stress distribution, which in turn increases web strength and beam capacity. Adding stiffeners and converting the flange plate to a triangle closed flange has the same effect of distributing the stresses in the web below the stiffener conjunction to the web. However, the stiffener effect is pronounced for small web thickness, while it diminishes as the web thickness increases. Fig. 16 presents the relationship between the capacity gain and the load width for different web and stiffener thicknesses. As shown in the figure, the normalized load is always above unity, representing the increase in web capacity after using a triangle closed flange. For the same t s /t w ratio, the normalized load remains constant, mainly for a small web thickness of 4 mm. By increasing t w to 6, then 8 mm, the normalized load decreases as the load length increases, indicating the stopping of the benefit of the stiffeners for thick webs. This is noticed significantly

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