Section Classification per EN 1993-1-1 Table 5.2

Before calculating beam resistance, classify the cross-section. The class determines the extent of the section that can be used in design:

For IPE sections in S355 steel (ε = √(235/355) = 0.814):

Bending Resistance — EN 1993-1-1 Clause 6.2.5

Class 1 and 2 Sections

M_c,Rd = M_pl,Rd = W_pl × f_y / γ_M0

Class 3 Sections

M_c,Rd = M_el,Rd = W_el,min × f_y / γ_M0

Class 4 Sections

M_c,Rd = W_eff,min × f_y / γ_M0

Where γ_M0 = 1.00 per EN 1993-1-1 Clause 6.1.

Worked Example — IPE 300 in S355

The design bending moment M_Ed must satisfy M_Ed / M_c,Rd ≤ 1.0.

Shear Resistance — EN 1993-1-1 Clause 6.2.6

V_c,Rd = V_pl,Rd = A_v × (f_y / √3) / γ_M0

For rolled I and H sections with load parallel to web:

A_v = A - 2 b t_f + (t_w + 2r) t_f

But not less than η × h_w × t_w where η = 1.0 (or 1.2 if using shear area enhancement).

IPE 300 Shear Capacity

For sections subject to high shear (V_Ed > 0.5 V_pl,Rd), reduce the bending moment resistance per Clause 6.2.7(3).

Lateral-Torsional Buckling — EN 1993-1-1 Clause 6.3.2

When the compression flange is not laterally restrained along its length, check LTB:

M_b,Rd = χ_LT × W_y × f_y / γ_M1

Where χ_LT is the reduction factor for LTB, determined from the slenderness λ_LT:

λ_LT = √(W_y × f_y / M_cr)

For a simply supported IPE 300 with 5 m span and uniform load:

The LTB reduction is significant (64% reduction) because the 5 m span provides no intermediate lateral restraint. Adding lateral restraints at third points would increase M_b,Rd substantially.

Combined Bending and Shear — Clause 6.2.7

When V_Ed ≥ 0.5 V_pl,Rd, the design plastic moment resistance is reduced:

M_y,V,Rd = M_pl,y,Rd × (1 - ρ)

Where ρ = (2 × V_Ed / V_pl,Rd - 1)²

If V_Ed < 0.5 V_pl,Rd, no reduction to the moment resistance is required.

Deflection Limits per EN 1990

EN 1990 Annex A1 recommends deflection limits:

For a 6 m beam, L/300 = 20 mm maximum deflection under imposed load.

Frequently Asked Questions

What section class is IPE 300 in S355 steel?

IPE 300 in S355 (ε = 0.814) has a flange c/tf ratio of 5.2, which is below the Class 1 limit of 9ε = 7.3. The web cw/tw ratio is 41.0, below 72ε = 58.6 for Class 1 in pure bending. Therefore IPE 300 is Class 1 in S355 steel.

When do I need to consider lateral-torsional buckling per EN 1993-1-1?

LTB must be checked per Clause 6.3.2 whenever the compression flange of a beam is not continuously restrained. For simply supported beams supporting a concrete slab connected with shear studs, the compression flange is usually restrained and LTB can be neglected. For unrestrained beams (e.g., crane girders, temporary works), LTB governs the design.

Related Pages

• Lateral-Torsional Buckling Guide — LTB per EN 1993-1-1 Clause 6.3.2
• Compact Section Limits — Class 1-4 per Table 5.2
• European Beam Sizes — IPE, HEA, HEB section dimensions
• EN 1993 Beam Design — Complete beam design guide
• Column Design Guide — Compression per EN 1993-1-1
• All European References

Educational reference only. Design per EN 1993-1-1:2005 + A1:2014. All values calculated per Eurocode 3 provisions. Verify section classification and resistance for actual loading conditions. Results are PRELIMINARY — NOT FOR CONSTRUCTION without independent verification.

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