Structural Steel Specification (Eurocode 3)

Overview

The Structural Steel Specification (Eurocode 3) skill assists Rakenne users in drafting and validating technical specifications for load-bearing steel structures across the EU. It covers the full EN 1993 framework including material selection (EN 10025-2 steel grades), partial safety factors from country-specific national annexes (γ_M0, γ_M1, γ_M2), cross-section classification, member design verifications (tension, compression, bending, buckling), connection design (EN 1993-1-8), and serviceability limit states. The skill includes reference tables, a comprehensive specification template, a compliance checklist, and two automated validation tools.

Getting Started

Add your project documentation to the workspace — structural drawings, load schedules, geotechnical reports — then activate the Structural Steel Specification (Eurocode 3) skill. The agent will guide you through the process step by step: defining the scope, selecting the target country’s national annex, specifying materials, elaborating loads and analysis, designing members and connections, and validating the final specification.

Example Conversation

A typical workflow for drafting a structural steel specification for a multi-storey building in Germany. The agent gathers context, applies the template, cross-references material codes, and runs the validation.

You: I need to draft a structural steel specification for a 4-storey office building in Munich, Germany. The structure is a braced frame with composite floors. We’re using S355 for primary members.

Agent: I’ll help you draft the specification under Eurocode 3 with the German national annex. Let me gather some details:

1. What are the approximate building dimensions (footprint and storey height)?
2. What is the consequence class — CC2 is typical for office buildings?
3. Are there any special requirements (seismic, fire rating, crane loads)?
4. Do you have the imposed floor loads or should I use the standard office category (Category B)?

You: Footprint is 30m × 18m, storey height 3.6m. CC2 is correct. Fire rating R60. No seismic. Standard Category B for offices plus a plant room on the roof at 7.5 kN/m².

Agent: I’ve retrieved the German national annex parameters using the code referencer tool. Key values for your specification:

• Steel grade S355 (EN 10025-2): f_y = 355 MPa (t ≤ 16 mm), f_y = 345 MPa (16 < t ≤ 40 mm), f_u = 510 MPa
• Partial safety factors (DIN EN 1993-1-1/NA:2015): γ_M0 = 1.00, γ_M1 = 1.10, γ_M2 = 1.25

Note that Germany has a higher γ_M1 = 1.10 for instability checks (buckling) compared to the Eurocode recommended value of 1.00. This affects all flexural and lateral-torsional buckling verifications.

I’ve applied the specification template and filled in the project-specific data. The document covers all 12 sections. I’d recommend we work on the load schedule and cross-section selection next. For the sub-grade, I suggest S355J2 given a minimum service temperature of −24 °C in Munich. Shall I elaborate the loads?

You: Yes, go ahead with the loads. Use snow zone 2 and wind zone 2 for Munich. Also check if S355J0 would be acceptable instead of J2.

Agent: I’ve completed the loads section with:

• Permanent: Self-weight (calculated) + floor finishes 1.5 kN/m² + partitions 0.8 kN/m² + services 0.25 kN/m²
• Imposed: 3.0 kN/m² (Cat. B offices, ψ_0 = 0.7), 7.5 kN/m² roof plant room (Cat. E storage, ψ_0 = 1.0)
• Snow: s_k = 1.09 kN/m² (zone 2, altitude 520 m per DIN EN 1991-1-3/NA)
• Wind: v_b,0 = 25.0 m/s (zone 2), peak velocity pressure depending on height and terrain category

Regarding the sub-grade: For S355 at 24 mm flange thickness and σ_Ed/f_y = 0.75, EN 1993-1-10 Table 2.1 gives a maximum permissible thickness of 25 mm for J0 at T_Ed = −24 °C. This is very tight — if any primary member exceeds 25 mm flange thickness, J0 would be inadequate. I recommend staying with S355J2 for the primary steelwork and using J0 only for secondary members (purlins, girts) with t ≤ 16 mm.

I’ve run the validation tool on the current draft. All 10 required sections are present. There are 18 placeholders remaining (connection details, base plate dimensions, and calculation references). The partial safety factors and yield strengths are correct. Shall I move on to the member design summary?

Sample Output Excerpt

A representative excerpt from a generated specification, showing the material specification and partial safety factors sections — critical areas where the skill ensures code conformity with the applicable national annex.

3. Material Specification

3.1 Structural steel grades

Notes:

• Yield strength f_y values are thickness-dependent per EN 10025-2, Table 7. Values shown correspond to the maximum thickness in each row.
• Sub-grade selection per EN 1993-1-10, Table 2.1, for minimum service temperature T_Ed = −24 °C (Munich, Germany), reference stress level σ_Ed / f_y = 0.75.
• Plates thicker than 40 mm: verify through-thickness properties (Z-quality per EN 10164) where lamellar tearing risk exists.

3.2 Bolt grades

3.3 Weld consumables

Weld consumables to have yield and tensile strengths ≥ parent material per EN 1993-1-8 §4.2. For S355 parent steel: minimum classification E 42 (EN ISO 2560). Correlation factor β_w = 0.9.

6.2 Partial safety factors

Design resistance formulas (key members):

Tension:       N_t,Rd = A × f_y / γ_M0 = A × 345 / 1.00
Compression:   N_c,Rd = A × f_y / γ_M0 = A × 345 / 1.00
Bending:       M_c,Rd = W_pl × f_y / γ_M0 = W_pl × 345 / 1.00
Buckling:      N_b,Rd = χ × A × f_y / γ_M1 = χ × A × 345 / 1.10
LT Buckling:   M_b,Rd = χ_LT × W_pl × f_y / γ_M1 = χ_LT × W_pl × 345 / 1.10
Bolt shear:    F_v,Rd = α_v × f_ub × A_s / γ_M2

This excerpt is illustrative. Final content must reflect project-specific data, analysis results, and engineering judgement.

Built-in Validation Tools

The skill includes two extension tools that automate code-conformity checks during specification drafting.

Tool 1: check_yield_safety_margin

Scans a structural steel specification (Markdown) and validates numerical values against the applicable Eurocode 3 requirements.

Tool 2: structural_code_referencer

Cross-references material properties and national annex data for a given steel grade and country.

Example validation output

====================================================================
Validation — Structural Steel Specification (Eurocode 3)
File: output/steel_spec_munich_office.md
National annex: Germany (DIN EN 1993-1-1/NA:2015)
====================================================================

--- Required specification sections ---
  [OK] Project description / scope
  [OK] Design codes and standards
  [OK] Material specification
  [OK] Design loads / actions
  [OK] Structural analysis
  [OK] Member design / verification
  [OK] Connection design
  [OK] Stability and buckling
  [OK] Serviceability limit state (SLS)
  [OK] Fire design (if applicable)

--- Steel grades detected ---
  S355 (EN 10025-2): f_y = 355 MPa (t ≤ 16 mm), f_u = 510 MPa

--- Partial safety factors (national annex minimums) ---
  γ_M0 ≥ 1.0  |  γ_M1 ≥ 1.1  |  γ_M2 ≥ 1.25
  γ_M0 values in document: 1
  γ_M1 values in document: 1.1
  γ_M2 values in document: 1.25

--- Yield strength values in document ---
  f_y values found: 355 MPa, 345 MPa, 335 MPa

--- Unfilled placeholders (18) ---
  - [base plate dimensions]
  - [anchor bolt layout]
  - [calculation reference]
  ... and 15 more

====================================================================
RESULT: No critical errors — basic structure and values conform

Warnings:
  - 18 unfilled placeholder(s) found
====================================================================

The agent runs validation automatically after significant edits and surfaces findings inline, so you always know exactly what remains before the specification is complete.