Preliminary beam sizing for steel (EC3) and concrete (EC2) structures. Calculate design bending moments, shear forces, section selection, deflection checks and utilisation ratios for simply supported, cantilever and continuous spans.
Important: This tool provides preliminary sizing only. All structural designs must be verified by a chartered structural engineer. Output is not suitable for use in construction documents.
Important Disclaimer — Read Before Use: This tool provides preliminary sizing only based on simplified elastic analysis. Results assume uniform loading, prismatic sections and standard material properties. No account is taken of lateral torsional buckling, connection design, dynamic loading, seismic actions, ground conditions, construction sequence or second-order effects. All structural designs must be verified by a chartered structural engineer. Output is not suitable for use in construction documents, building regulations submissions or tender packages.
Ultimate Limit State (ULS) checks ensure the beam will not collapse under factored design loads, verifying that applied bending moment (M⊂Ed) and shear force (V⊂Ed) do not exceed the section’s design resistances (M⊂c,Rd and V⊂c,Rd). Serviceability Limit State (SLS) checks ensure that deflections, vibrations and crack widths under characteristic loads do not impair the function or appearance of the structure. For steel beams, the standard deflection limit under imposed load is span÷360. For concrete, crack width is limited to 0.3 mm under quasi-permanent loading per EC2 Table 7.1.
Composite construction — a steel beam acting compositely with a concrete slab via shear connectors — is appropriate for typical floor beams in multi-storey buildings where a concrete deck is present. Full composite action increases the effective second moment of area by 2–3 times compared to the bare steel section, allowing section depths to be reduced by approximately 20–30% or span-to-depth ratios to increase to around L/20–L/24. The composite section must satisfy EC4 requirements; this tool uses a simplified elastic composite section estimate. A detailed design must account for partial interaction, construction stage loading and long-term creep effects.
As a rough preliminary guide: simply supported steel beams — L/20 to L/25; simply supported concrete beams — L/12 to L/16 (with appropriate reinforcement); cantilever steel — L/7 to L/10; cantilever concrete — L/6 to L/8. Composite steel-concrete beams can achieve L/22 to L/28 at full composite action. These ratios are starting points only; actual depths depend on load intensity, deflection limits, lateral support conditions and acoustic requirements. Always confirm sizing with a structural engineer using full analysis software.
Our structural engineering team delivers EC2 and EC3 compliant beam, column and slab designs from concept through to construction issue — including full calculations, drawings and building regulations coordination.
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