Issue 78

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

thickness of 8 mm, the rectangular stiffening gives a higher strengthening effect of about 10% than the triangular stiffening. This behaviour is noticed for both load lengths of 75 and 150 mm. Despite the advantage of the angle for giving higher capacity, there is a cost associated with increasing the amount of steel, as long as the length of the angle legs is larger than the inclined plate length. The stiffener in the triangular flange has a length of 116.6 mm [sq. root of 60^2+100^2] , whereas the stiffener in the rectangular flange has a length of 160 mm [width 60 mm + depth 100 mm] . These lengths are for one side of stiffening only. To verify the worthiness of using angles instead of inclined plates in the stiffening, a stiffener area comparison is conducted for different loading lengths. The thickness of the angles is reduced to give a fair comparison and the same cross-sectional area as the inclined plates. Tab. 3 summarizes the dimensions used in the comparison and the amount of steel that is added to the original I-sections for stiffening the flat flange. As shown in Fig. 19, the triangular shape strengthening provides higher strength for the same amount of steel material than the rectangular closed shape strengthening. Using angles adds no value to the web capacity. This is also noticed in Fig. 20, where the von Mises stresses have a better distribution for the triangle flange than the rectangular one. It is worth mentioning that this conclusion is related to the web capacity only, while a different conclusion may be found if the study is conducted on the flexural capacity of the beam. Shape of closed top flange Stiffener thickness (t s ) (mm) Stiffener length (mm) Stiffener area at one side (mm) 2 Rectangular 3 160 480

Indicated in Figure 19 as average area of 475 sq.mm Indicated in Figure 19 as average area of 950 sq.mm

Triangular Rectangular Triangular

4 6 8

117 160 117

468 960

936 Table 3: Equivalent area configurations for triangular and rectangular closed top flanges.

Figure 18: Stiffener thickness versus normalized Load for closed and triangular stiffened flange.

Figure 19: Stiffener’s shape area effect.

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