Issue 78

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

counteracting the imposed load. As a result, the load-bearing function is more equally distributed across the girder's depth, resulting in a significant improvement in structural efficiency and maximum load capacity.

Figure 11: von-Mises stresses for stiffened girder with h w = 500 mm, t w = 4 mm, and t s = 4 mm.

In the next sections, the curves are plotted with the normalized load on the vertical axis, presenting the ratio between the load of the I-section with a triangle stiffening configuration and the one with a conventional flange plate. All values are higher than unity, representing the gain in the web strength after performing the triangle configuration. In the following, the effect of each parameter is discussed, namely the stiffener thickness, web thickness, loaded length, depth of stiffened web, and shape of closed flange; triangular and rectangular configurations. Effect of stiffener thickness (ts) The thickness of the stiffener plate that forms the triangle flange and supports the web positively affects web strength gain. As shown in Fig. 12, for the relation between the normalized load and the stiffener thickness, the relation is proportional, and as the stiffener thickness increases, the strength gain increases. Stiffener classification contributes effectively to increasing patch load resistance. As a compact stiffener remarkably increases strength, slender stiffeners slightly affect the strength gain. For small t s of 1 and 2 mm, the gain in strength is limited to 10-20% only (normalized load = 1.1 to 1.2). The gain rapidly increases with the increase of t s , noticeable for the small web thickness and small loaded length. For t w = 4 mm and W = 0, the normalized load is almost 6.0 for t s = 24 mm. This ratio becomes 2.2 for t w = 8 mm, W = 150 mm, and t s exceeding 15 mm. Compared to the classification of the stiffener plate, as compact, non-compact, or slender, a curve is presented between the normalized load versus the slenderness ratio (Ls/t s ), as shown in Fig. 13. As for noncompact stiffeners with Ls/t s = 30 (t s around 4 mm), they have a moderate gain of around 50% to 150%. With a slender stiffener, the effect of the stiffener is nearly constant, having less gain. Increasing stiffener thickness to 6 mm, toward compact classification with Ls/t s = 20, shows higher gain, 100% for t w = 8 mm and 200% for t w = 4 mm. As a conclusion, it can be recommended to use a stiffener with a length-to-thickness ratio in the range of 10 to 20 to gain considerable strength without adding much weight, given the low value for the small web thickness. Varying loading length does not affect this behavior,

and it remains the same. Effect of web thickness (t w )

Increasing web thickness generally increases the web capacity. However, the positive effect of the triangle flange is more noticeable in the thinner web than in the thicker one. As shown in Fig. 14, for the relationship between the normalized load and the web thickness, the lower the web thickness is, the higher the strength gains. This observation is found in the same manner for different loaded lengths, while it is more noticeable when using a higher thickness of the stiffener. As shown in

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