EN 1994-1-1 Composite Steel-Concrete Design

Automated composite beam and column design per EN 1994-1-1:2004. Covers the full design workflow from effective width through plastic moment resistance, shear connector design, transverse reinforcement, and long-term deflection.

Tier: All three endpoints (beam, column, shear-connection) require a Pro or Studio subscription. Free tier returns HTTP 402 with an upgrade URL.

API Endpoints

Design one or more composite beams. Computes effective width, plastic moment resistance (full and partial interaction), shear connector count and spacing, transverse reinforcement in slab, and deflection (short + long-term).

Design encased or concrete-filled tube (CFT) composite columns. Computes plastic axial resistance, Euler buckling loads, second-order moment magnification, and biaxial N-M interaction.

Degree of shear connection η, η_min per Table 6.2, partial-interaction curve (M_pl,Rd vs η), stud spacing limits, and edge distance check.

National Annex factor lookup — informational, no auth required.

Beam Design — POST /api/composite/beam

Designs composite steel beams with headed stud shear connectors per EN 1994-1-1 §5.4.1.2, §6.2.1, §6.6, and §7.3.1.

Request

{
  "email": "engineer@firm.com",
  "na_code": "recommended",            // 'recommended'|'NL'|'DE'|'FR'|'IT'
  "beams": [{
    "mark": "CB-A1",
    "profile": "IPE 400",              // or supply steelSection directly
    "steelSection": {
      "A_mm2": 8446, "I_y_mm4": 231300000,
      "h_mm": 400, "b_f_mm": 180, "t_f_mm": 13.5, "t_w_mm": 8.6,
      "f_y_MPa": 355
    },
    "slab": { "h_c_mm": 150, "b_eff_mm": 2000, "fck": 30 },
    "span_mm": 8000,
    "b_left_mm": 3000,
    "b_right_mm": 3000,
    "studs": { "d_mm": 19, "h_sc_mm": 95, "f_u_MPa": 450, "spacing_mm": 150 },
    "M_Ed_kNm": 500,
    "loads": { "G_kN_m": 12, "Q_kN_m": 18, "shrinkage_strain": 0.000325 },
    "eta": 1.0
  }]
}

Response fields

Column Design — POST /api/composite/column

Designs composite columns (encased I-section or CFT) per EN 1994-1-1 §6.7.2/§6.7.3, with second-order effects per §5.8.3.

Request

{
  "email": "engineer@firm.com",
  "na_code": "recommended",
  "columns": [{
    "mark": "CC-1",
    "type": "encased",                // 'encased' | 'cft_rect' | 'cft_circ'
    "N_Ed_kN": 2000,
    "M_Ed_xx_kNm": 150,               // strong axis
    "M_Ed_yy_kNm": 50,                // weak axis
    "steelSection": { "A_a_mm2": 18270, "h_mm": 300, "b_f_mm": 300,
                       "t_f_mm": 19, "t_w_mm": 11, "f_y_MPa": 355,
                       "I_xx_mm4": 251700000 },
    "concrete": { "A_c_mm2": 153730, "fck": 30 },
    "rebar": { "A_s_mm2": 1600, "fyk": 500, "gamma_s": 1.15 },  // encased only
    "l_0_x_mm": 3000,
    "l_0_y_mm": 3000
  }]
}

Response fields

Shear Connection — POST /api/composite/shear-connection

Returns η_min, connector count, spacing verification, edge distance check, and the partial-interaction M_pl,Rd vs η curve for each beam.

Worked Example — Office Floor Composite Beam

Structure: Simply-supported 8 m office floor beam. IPE 400 steel, 150 mm concrete slab (C30/37), b_eff = 2 000 mm, 19 mm headed studs @ 150 mm spacing.

At M_Ed = 500 kNm, utilisation = 500/692 = 0.72 — PASS.

National Annex Variants

Four NA codes are supported. The Dutch (NL) NA raises α_cc to 1.00 for concrete, increasing f_cd and thus M_pl,Rd and N_pl,Rd.

IFC 4 Integration

Composite beams exported via /api/export (IFC4) include the full composite model:

• IfcBeam — steel I-section, S355, extruded from the steel profile definition
• IfcSlab — concrete topping, effective width × slab depth × span, C{fck}/37
• IfcMechanicalFastener — one entity per headed stud, placed at stud spacing along the beam, user-defined type SHEAR_STUD

References

• EN 1994-1-1:2004 — Eurocode 4: Design of composite steel and concrete structures — Part 1-1: General rules and rules for buildings
• NEN-EN 1994-1-1/NA:2011 — Netherlands National Annex (α_cc = 1.00)
• DIN EN 1994-1-1/NA:2010 — Germany National Annex
• NF EN 1994-1-1/NA:2007 — France National Annex
• UNI EN 1994-1-1/NA:2009 — Italy National Annex
• SCI P405 — Design of Composite Beams using Precast Concrete Slabs
• EN 1993-1-1:2005 — Steel design (γ_M0, γ_M1 for steel section resistance)
• EN 1992-1-1:2004 — Concrete design (f_cd, E_cm for slab action)

Last reviewed: 2026-06-08