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Per EN 1993-1-1 Table 5.2, a web in pure bending is Class 3 when h_w/t_w ≤ 124ε (where ε = √(235/f_y)). If h_w/t_w exceeds this limit, the web is Class 4 and an effective section must be used. For S355 the Class 3 limit is about 101; typical bridge plate girders with h_w/t_w = 120–200 will be Class 4.
How is the effective section for a Class 4 web calculated?
EN 1993-1-5 §4 uses the reduced-section approach. The plate slenderness λ̄_p = (h_w/t_w)/(28.4·ε·√k_σ) is computed using k_σ = 23.9 for an internal element in pure bending (ψ = −1, Table 4.1). The reduction factor ρ = (λ̄_p − 0.22)/λ̄_p² for λ̄_p > 0.673, giving effective width b_eff = ρ·h_w distributed 40%/60% from the compressed edge.
What is the flange-induced buckling check in §8.1?
EN 1993-1-5 §8.1 limits web slenderness to prevent the compression flange from inducing out-of-plane buckling of the web: h_w/t_w ≤ k·(E/f_yf)·√(A_fc/A_w), where k = 0.55 for Class 4 sections (elastic design). This check is often satisfied for standard plate girder proportions but can govern for very slender webs with narrow flanges.
How is the transverse stiffener checked per §9.1?
Each transverse stiffener must have a minimum second moment of area (Eq 9.1): I_st ≥ 0.75·h_w·t_w³ for a/h_w ≥ √2, or 1.5·h_w³·t_w³/a² for closer spacing. The effective stiffener cross-section (plate + adjacent web strip 15ε²t_w each side) is then checked for column buckling (curve c, α = 0.49) under the applied shear force N_Ed = V_Ed.
What is the M-V interaction check in §7.1?
When V_Ed > 0.5·V_b,Rd and M_Ed > 0, EN 1993-1-5 §7.1 Eq.7.1 requires: (2·V_Ed/V_b,Rd − 1)² + M_Ed/M_pl,Rd ≤ 1. For plate girders M_pl,Rd is taken as M_eff,Rd (the effective section bending resistance). The interaction ensures the flanges can carry bending after the web has yielded in shear.
Which partial factors apply for EN 1993-1-5 design?
EN 1993-1-1 §6.1 specifies γ_M0 = 1.00 for cross-section resistance and γ_M1 = 1.10 for member buckling resistance. The Netherlands NA (NEN-EN) and German NA (DIN-EN) both use γ_M1 = 1.10. All EN 1993-1-5 plate buckling and shear buckling checks use γ_M1 = 1.10.