EN 1993 Beam Design — Flexural Design per Eurocode 3 Clause 6.2

Q: 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.

Q: 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.

Complete guide to steel beam flexural design per EN 1993-1-1:2005 Clauses 6.2.5 (bending), 6.2.6 (shear), 6.2.7 (bending and shear), and 6.3.2 (lateral-torsional buckling). Section classification per EN 1993-1-1 Table 5.2, worked example with IPE 300 in S355 steel.

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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:

Class	Criterion	Design Approach
1	Plastic hinge with rotation	Full plastic moment Mpl,Rd, rotation capacity for plastic analysis
2	Plastic moment capacity	Full plastic moment Mpl,Rd, limited rotation capacity
3	Elastic capacity	Elastic moment Mel,Rd, yield stress at extreme fibre
4	Local buckling governs	Effective section, reduced moment Meff,Rd per EN 1993-1-5

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

Section	Flange c/tf	Class (flange)	Web cw/tw	Class (web bending)
IPE 300	5.2	1	41.0	1
IPE 400	5.6	1	45.6	1
IPE 500	5.9	1	49.6	2
IPE 600	6.4	2	53.0	2

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

Property	Value
Section	IPE 300
Steel grade	S355 (fy = 355 MPa)
W_pl,y	628.4 cm³
W_el,y	556.0 cm³
I_y	8356 cm⁴
Class	1
M_pl,Rd	628.4×10³ × 355 / 1.00 = 223.1 kN·m
M_el,Rd	556.0×10³ × 355 / 1.00 = 197.4 kN·m

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

Property	Value
A_v	2190 mm²
V_pl,Rd	2190 × 205 / 1.00 = 448.5 kN

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:

Parameter	Value
M_cr	89.4 kN·m
λ_LT	1.58
χ_LT (curve a)	0.36
M_b,Rd	0.36 × 223.1 = 80.3 kN·m

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:

Condition	Limit
Vertical deflection (beams)	L/200
Deflection under imposed load (w2)	L/300
Deflection under live load (w3)	L/350
Cantilever deflection	L/150

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?