Issue 78

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

there is an increase in the capacity of around 1.4 times. Better stress distribution along the depth of the web is recorded as the web thickness increases, as shown in Fig. 10.

Figure 9: Load versus vertical displacement under the loaded point for models with different loaded lengths at a) t w = 4 mm, b) t w = 6 mm, and t w = 8 mm.

Figure 10: von-Mises stresses for unstiffened girder with h w = 500 mm and W = 0 for models with a) t w = 4 mm, b) t w = 6 mm, and c) t w = 8 mm.

I- SECTION WITH CLOSED FLANGE UNDER PATCH LOADING

A

closed flange greatly increases web capacity when compared to beams with a normal flange plate. For cases of low load lengths, the unstiffened girder failed just beneath the loaded flange. The use of a triangle closed flange altered the load-transfer mechanism significantly, as shown in Figure 11 for von-Mises stresses of a stiffened beam with a triangle top flange and different load lengths. The concentrated patch load on the top flange is distributed over a larger horizontal area in the stiffeners before it impacts the web. The previously concentrated load is converted into a more uniformly distributed line load, lowering concentrations of local stress and delaying web crippling and local buckling. When longer loaded lengths are applied to unstiffened specimens, a concentrated, highly stressed patch formed along the flange web junction, indicating that failure was caused by web crippling and localized folding near the loaded flange. However, adding stiffeners had a considerable impact on stress distribution. Peak stress shifted away from the flange-web contact and deeper into the web, resulting in a broad, curved stress distribution comparable to a yield line mechanism. This suggests that stiffeners generate a rigid load-transfer zone at the top of the beam, thereby preventing deformation along the upper web part and reducing the vulnerable unsupported depth of the web. Triangle stiffeners aid in preventing premature local buckling and reinforce the flange-web connection, moving the buckling mechanism to a lower point within the web plate. This change also contacts a considerably larger amount of the web surface,

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