Issue 78

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

The results show that all ultimate loads by codes are lesser than FEM results, showing P FEM /P code larger than unity. Taking the limit of stiffener stiffness into account as per code gives high conservatism with P FEM /P code in range of 2.4 to 4.75. By ignoring the limitation and calculating the exact stiffener stiffness, the code gives more reliable values with P FEM /P code in range of 1.54 to 2.93. The FE-to-code gap is significantly reduced by considering in the code equations the unlimited stiffener rigidity. It can be concluded that the longitudinal stiffener rigidity has a major impact on web failure processes under patch loading, hence it is important to accurately characterize stiffener restraint during analysis, underscoring the need for additional research beyond EN 1993-1-5 norms. Overall, for the examined triangular and rectangular closed flange designs, the FE-to-code evaluation shows that EN 1993 1-5 is applicable and can be used to estimate the web capacity to the safe side, with recommendation to ignore the upper limit of the stiffener stiffness.

Figure 21: Effect of the γ s ∗ rigidity limit on the P FEM to-P code resistance ratios of triangular and rectangular flange stiffening configuration. Specimen γ s ,calc. γ s *

P code following γ s * limit (kN)

P FEM /P code following γ s * limit

P FEM /P code without γ s *limit

P FEM (kN)

P code without γ s *limit (kN)

T-500-4/4-0 T-500-4/4-75 T-500-4/4-150 T-500-6/4-0 T-500-6/4-75 T-500-6/4-150 T-500-8/4-0 T-500-8/4-75 T-500-8/4-150 R-500-4/4-0 R-500-4/4-75 R-500-4/4-150 R-500-6/4-0 R-500-6/4-75 R-500-6/4-150 R-500-8/4-0 R-500-8/4-75 R-500-8/4-150

323.04 498.70 584.68 392.64 613.50 684.42 470.78 675.33 756.90 325.88 474.46 535.62 390.86 618.08 691.02 471.70 739.66 861.45

338.93 338.93 338.93 414.95 414.95 414.95 480.36 480.36 480.36 764.81 764.81 764.81 996.88 996.88 996.88 1212.65 1212.65 1212.65

34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34 34

134.47 159.74 181.53 134.47 159.74 181.53 134.47 159.74 181.53 134.47 159.74 181.53 134.47 159.74 181.53 134.47 159.74 181.53

182.49 216.79 246.36 188.88 224.38 254.99 193.77 230.19 261.59 210.93 250.57 284.75 221.88 263.59 299.54 230.57 273.91 311.27

2.40 3.12 3.22 2.92 3.84 3.77 3.50 4.23 4.17 2.42 2.97 2.95 2.91 3.87 3.81 3.51 4.63 4.75

1.77 2.30 2.37 2.08 2.73 2.68 2.43 2.93 2.89 1.55 1.89 1.88 1.76 2.35 2.31 2.05 2.70

2.77 Note: Naming of specimens uses a letter at the beginning to define the top flange configurations triangular or rectangular (T or R). The letter is followed by groups of numbers in millimetres denoting the beam depth, firstly, then the stiffener thickness/web thickness, and lastly, the width of the patch load. Table 4: Comparison of FE and EN 1993-1-5 patch-loading resistances.

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