Eurocode 5 Timber Design Calculator (EN 1995-1-1)

Check timber beams and columns to Eurocode 5: bending, shear, axial and deflection with service class, load duration, kmod, kdef and partial factors.

Simplified educational tool – always verify final designs against EN 1995‑1‑1 and your National Annex.

Eurocode 5 Member Check

1. Member type & geometry

2. Timber strength class & Eurocode 5 parameters

Typical: 1.3 for solid timber, 1.25 for glulam (check National Annex).

Show characteristic strengths & stiffness (fk, E0,mean)

Values pre-filled for C24. Change strength class to auto-update; switch to “Custom” to edit freely.

Show kmod and kdef

These are estimated from service class and load duration. Override if your National Annex specifies different values.

3. Design actions (ULS) and loads (SLS)

Compression positive, tension negative.

Used for deflection check (SLS).

4. Deflection limit

Eurocode 5 Check Results

Section properties

Area A: – cm²

Section modulus W: – cm³

Second moment of area I: – cm⁴

Design strengths

fm,d (bending): – N/mm²

fv,d (shear): – N/mm²

fc,0,d (compression): – N/mm²

ULS utilization

Bending ηm,y = MEd / MRd –

Shear ηv = VEd / VRd –

Axial ηN = NEd / NRd –

Combined (approx.) –

Deflection (SLS)

Instantaneous deflection winst: – mm

Final deflection wfin (incl. creep): – mm

Limit: – mm

Utilization ηdefl –

Overall verdict

Run the calculation to see if the member passes Eurocode 5 checks.

Eurocode 5 timber design – what this calculator does

This tool implements a simplified Eurocode 5 (EN 1995‑1‑1) check for prismatic timber members. It is aimed at quick sizing, sanity checks and education, not as a full design package.

Checks included

  • Bending resistance about the strong axis (My).
  • Shear resistance parallel to grain.
  • Axial compression / tension resistance (no buckling curve – see note below).
  • Approximate combined bending + axial interaction.
  • Instantaneous and final deflection under uniform load.

Key Eurocode 5 formulas used

Design strengths

Characteristic strengths fk are converted to design strengths using kmod and γM:

\( f_{m,d} = \dfrac{k_{mod}\, f_{m,k}}{\gamma_M} \)
\( f_{v,d} = \dfrac{k_{mod}\, f_{v,k}}{\gamma_M} \)
\( f_{c,0,d} = \dfrac{k_{mod}\, f_{c,0,k}}{\gamma_M} \)

Section properties for a rectangular section

\( A = b \cdot h \)
\( W = \dfrac{b\,h^2}{6} \) (about the strong axis)
\( I = \dfrac{b\,h^3}{12} \)

Bending and shear resistance

\( M_{Rd} = f_{m,d} \cdot W \)
\( V_{Rd} = f_{v,d} \cdot A \)

Utilization ratios:

\( \eta_m = \dfrac{M_{Ed}}{M_{Rd}} \quad;\quad \eta_v = \dfrac{V_{Ed}}{V_{Rd}} \)

Axial resistance (no buckling)

For pure compression or tension without stability effects:

\( N_{Rd} = f_{c,0,d} \cdot A \quad (\text{compression}) \)
\( N_{Rd} = f_{t,0,d} \cdot A \quad (\text{tension, using } f_{t,0,k}) \)

The calculator uses compression resistance for NEd > 0 and tension resistance for NEd < 0. Column buckling per EC5 §6.3 is not implemented – you must check slender members separately.

Combined bending and axial (simplified)

For quick assessment, a simple interaction is used:

\( \eta_{comb} = \eta_m + \eta_N \)

where \( \eta_N = N_{Ed} / N_{Rd} \). In a rigorous design you should follow the interaction expressions in EN 1995‑1‑1 §6.

Deflection and creep

For a simply supported beam with uniform load q (kN/m), the instantaneous midspan deflection is:

\( w_{inst} = \dfrac{5\,q\,L^4}{384\,E_{0,mean}\,I} \)

with q in N/mm, L in mm, E in N/mm² and I in mm⁴. Final deflection including creep is approximated as:

\( w_{fin} = w_{inst} \cdot (1 + k_{def}) \)

Typical choices for kmod and kdef

Eurocode 5 provides tables for kmod and kdef depending on service class and load duration. This calculator uses representative values such as:

  • Service class 1, medium-term: kmod ≈ 0.8, kdef ≈ 0.6
  • Service class 2, medium-term: kmod ≈ 0.7, kdef ≈ 0.8
  • Service class 3, permanent: kmod ≈ 0.45, kdef ≈ 2.0

Always check the exact values in EN 1995‑1‑1 and your National Annex.

Limitations and engineering responsibility

  • Only prismatic rectangular members are covered.
  • No lateral torsional buckling, column buckling curves or stability of frames.
  • No checks for connections, notches, holes, fire design or vibration.
  • National Annex adjustments (γM, kmod, kdef, ψ factors) are not applied automatically.

Use this tool for preliminary sizing and teaching. Final designs must be checked by a qualified structural engineer using the full Eurocode 5 provisions and project-specific requirements.

Worked example

Consider a simply supported C24 beam, b = 100 mm, h = 300 mm, span L = 4.0 m, service class 2, medium-term load, γM = 1.3, uniform characteristic load qk = 5 kN/m.

  1. Section modulus \( W = b h^2 / 6 = 100 \cdot 300^2 / 6 = 1.5 \times 10^6 \,\text{mm}^3 \).
  2. Assume MEd = 30 kNm → 30×106 Nmm.
  3. With fm,k = 24 N/mm², kmod = 0.7, γM = 1.3:
    fm,d = 0.7·24 / 1.3 ≈ 12.9 N/mm².
  4. MRd = fm,d·W ≈ 12.9·1.5×106 ≈ 19.4×106 Nmm = 19.4 kNm.
  5. Bending utilization ηm = 30 / 19.4 ≈ 1.55 → beam is overstressed in bending.

Increasing the depth to 350 mm or choosing a higher strength class (e.g. C30) will quickly show whether the design becomes adequate.

FAQ

Can I use this for glulam beams?

Yes. Select GL24h or GL28h to load typical glulam properties. For other grades, switch to “Custom” and enter the characteristic strengths from the manufacturer or standard.

How should I input loads?

Enter design values MEd, VEd, NEd obtained from your load combinations per EN 1990 and EN 1991. The uniform load qk is the characteristic value used for deflection checks at SLS.

Where do the default strength values come from?

The default fk and E0,mean values are based on typical tables for softwood strength classes (C16–C30) and glulam (GL24h, GL28h). Always confirm against the current version of EN 338 and your material specifications.