Fire Resistance Ratings (EN 13501-2)

R = load-bearing capacity (Resistance) in minutes.

Critical Temperature Method (EN 1993-1-2 Cl. 4.2.4)

The design resistance of a steel member in fire is:

N_fi,t,Rd = k_y,theta x N_Rd / gamma_M,fi

Where:

• k_y,theta = reduction factor for yield strength at temperature theta
• gamma_M,fi = 1.00 (partial factor for fire)

Steel Strength Reduction at Elevated Temperature (EN 1993-1-2 Table 3.1)

Critical Temperature for Load Level

Section Factor A_m/V (EN 1993-1-2 Cl. 4.2.5)

A_m/V = exposed surface area / steel volume (m^-1)

Worked Example — IPE 330 Beam, R60 Fire Rating

Beam: IPE 330, S355, simply supported, 6.0 m span, eta_fi = 0.55

A_m/V = 2 x 0.330 / 0.006260 = 105 m^-1 Critical temperature: T_cr = 575 C (from Table 3.1)

For A_m/V = 105 m^-1 and R60: intumescent coating at 1.0 mm DFT.

Design Applications

Common Design Scenarios

This reference covers structural design scenarios commonly encountered in structural steel design practice:

• Strength verification: Check member or connection capacity against factored loads per the applicable design code
• Serviceability checks: Verify deflections, vibrations, and other serviceability criteria
• Code compliance: Ensure design meets all provisions of the governing standard
• Connection detailing: Verify weld sizes, bolt quantities, and edge distances

Related Design Considerations

• System behavior: consider the interaction between members and connections
• Load paths: verify that forces can be transferred through the structure to the foundations
• Constructability: check that the design can be fabricated and erected practically
• Cost optimisation: evaluate alternative sections or connection types for economy

Worked Example

Problem: Verify a typical steel member for the following conditions:

Typical span: 6.0 m | Load: service loads per applicable code | Section: common section in this category

Design Check:

1. Determine governing load combination (ULS or SLS per EN 1990)
2. Calculate maximum internal forces (moment, shear, axial)
3. Compute nominal capacity per code provisions
4. Apply resistance/safety factors
5. Verify interaction if combined forces exist

Result: Use the results from the Steel Calculator tool to verify design adequacy.

Design Applications

Common Design Scenarios

This reference covers structural design scenarios commonly encountered in structural steel design practice:

• Strength verification: Check member or connection capacity against factored loads per the applicable design code
• Serviceability checks: Verify deflections, vibrations, and other serviceability criteria
• Code compliance: Ensure design meets all provisions of the governing standard
• Connection detailing: Verify weld sizes, bolt quantities, and edge distances

Related Design Considerations

• System behavior: consider the interaction between members and connections
• Load paths: verify that forces can be transferred through the structure to the foundations
• Constructability: check that the design can be fabricated and erected practically
• Cost optimisation: evaluate alternative sections or connection types for economy

Worked Example

Problem: Verify a typical steel member for the following conditions:

Typical span: 6.0 m | Load: service loads per applicable code | Section: common section in this category

Design Check:

1. Determine governing load combination (ULS or SLS per EN 1990)
2. Calculate maximum internal forces (moment, shear, axial)
3. Compute nominal capacity per code provisions
4. Apply resistance/safety factors
5. Verify interaction if combined forces exist

Result: Use the results from the Steel Calculator tool to verify design adequacy.

Frequently Asked Questions

What European Standard governs structural steel design?

EN 1993 (Eurocode 3: Design of Steel Structures) is the primary standard for structural steel design in Europe. EN 1993-1-1 covers general rules for buildings, EN 1993-1-8 addresses connection design, and EN 1993-1-2 covers fire design. The standard uses limit state design with partial safety factors (γM). National Annexes adapt parameters to each member state. Companion standards include EN 10025 for hot-rolled products, EN 1090 for execution, and EN 1994 for composite design.

What are the common steel grades used in European construction?

The most common steel grades for European construction are S235, S275, S355, S420, and S460 per EN 10025-2. S355 (minimum yield 355 MPa for t ≤ 16 mm) is the most widely used for structural applications. S275 is used for secondary members. S420 and S460 are quenched and tempered high-strength steels for weight-critical applications. Weathering steel (S355J2W) and fine-grain structural steels (EN 10025-3 and -4) are also available.

How does EN 1993 compare to other international steel design codes?

EN 1993, AISC 360 (US), AS 4100 (Australia), and CSA S16 (Canada) all use limit states design principles but differ in key details. EN 1993 uses partial safety factors (γM0 = 1.00, γM1 = 1.00, γM2 = 1.25) rather than resistance factors (φ). Buckling curves in EN 1993 follow the European Column Curve system (a0 to d) with 5 distinct curves, compared to AISC's single curve. EN 1993-1-8 has comprehensive connection design provisions including the component method for moment connections.

Frequently Asked Questions

What is the critical temperature method in EN 1993-1-2?

The critical temperature method compares the steel temperature under the standard fire to the temperature at which the member load-bearing capacity equals the applied load. For typical load levels (eta_fi = 0.5-0.6), critical temperatures range from 550 to 600 C. If the unprotected steel temperature rise exceeds this, fire protection is required.

What is the section factor A_m/V and why does it matter?

A_m/V is the ratio of heated surface area to steel volume. A high section factor means a slender section that heats up quickly (CHS 48.3x4: ~280 m^-1) vs a heavy section that heats slowly (HEB 300: ~60 m^-1). Protection thickness requirements are directly related to A_m/V.

Related Pages

• European Steel Properties
• Beam Design
• Column Design
• All European References

Educational reference only. Fire design per EN 1993-1-2:2005. Verify protection thicknesses with manufacturer data. Results are PRELIMINARY - NOT FOR CONSTRUCTION without independent verification.