Which Eurocode clauses does this bolted connection calculator follow?

The calculator is based on EN 1993-1-8:2005 (Eurocode 3 – Design of steel structures – Part 1-8: Design of joints). In particular it follows the resistance expressions for bolt shear, bearing, tension and combined loading from clauses 3.6 and 3.8, and slip resistance for preloaded connections from clause 3.9. Partial factors are taken from EN 1993-1-8 and EN 1990.

Can I use this tool for both preloaded and non-preloaded bolts?

Yes. For non-preloaded bolts the calculator checks shear, bearing and tension resistances of the bolt and connected plates. For preloaded (HSFG) bolts you can additionally check slip resistance at the ultimate or serviceability limit state by selecting the appropriate slip factor and partial factor.

Does the calculator support combined shear and tension in bolts?

Yes. When both shear and tension are present, the calculator applies the Eurocode 3 interaction criterion for combined loading. It reports the utilisation ratio for shear, tension and the interaction check so you can see which condition governs the design.

What assumptions does this Eurocode 3 bolted connection calculator make?

The tool assumes standard metric bolt sizes (M12–M30) in steel plates with uniform thickness, double-shear or single-shear lap/cover plate arrangements, and bolts in standard holes. It does not currently model prying forces, block shear of the connected plate, or complex 3D load paths. These effects should be checked separately where relevant.

Eurocode 3 Bolted Connection Design Calculator (EN 1993‑1‑8)

Design and check steel bolted connections to Eurocode 3 (EN 1993‑1‑8): shear, tension, combined loading, bearing and slip resistance for preloaded and non‑preloaded bolts.

Bolted Connection Inputs

Connection & Bolt Type

Connection type Shear plane configuration Bolt diameter d (mm) Bolt grade Number of bolts in the critical row

Plate Geometry & Material

Plate thickness t (mm) Steel grade (plate) End distance e₁ (mm) Edge distance e₂ (mm) Hole type

Design Actions (per connection)

Design shear force V_Ed (kN) Design tension force N_Ed (kN)

γ_M2 (bolts in shear/tension)

γ_M3 (slip resistance)

γ_Mb (bearing)

Design Results (per connection)

Summary

Enter data and click “Calculate” to see utilisation ratios and governing failure mode.

Bolt Shear & Tension (EN 1993‑1‑8, 3.6)

Shear resistance per bolt V_Rd = – kN
Tension resistance per bolt N_Rd = – kN
Design shear per bolt V_Ed,bolt = – kN
Design tension per bolt N_Ed,bolt = – kN
Shear utilisation η_V = –
Tension utilisation η_N = –
Interaction check η_V+N = –

Bearing & Slip Resistance

Bearing resistance per bolt F_b,Rd = – kN
Bearing utilisation η_b = –
Slip resistance per bolt F_sl,Rd = – kN
Slip utilisation η_sl = –

Governing Check

–

How this Eurocode 3 bolted connection calculator works

This tool implements the main resistance checks for steel bolted connections according to EN 1993‑1‑8:2005 (Eurocode 3 – Design of steel structures – Part 1‑8: Design of joints). It is intended as a fast design aid and teaching tool; it does not replace a full code check by a qualified engineer.

1. Bolt material properties

For standard metric bolts, Eurocode 3 defines the ultimate tensile strength \( f_{ub} \) and the yield strength \( f_{yb} \) from the bolt grade (e.g. 8.8, 10.9). The calculator uses:

Grade 4.6: \( f_{ub} = 400 \,\text{MPa} \)
Grade 8.8: \( f_{ub} = 800 \,\text{MPa} \)
Grade 10.9: \( f_{ub} = 1000 \,\text{MPa} \)

The tensile stress area \( A_s \) is approximated from the nominal diameter \( d \) using standard ISO values (e.g. M20 → \( A_s \approx 245 \,\text{mm}^2 \)).

2. Bolt shear resistance (clause 3.6)

For a bolt in shear: \[ V_{Rd} = \frac{\alpha_v \, f_{ub} \, A_s}{\gamma_{M2}} \] where:

\( \alpha_v \) – shear factor (typically 0.6 for non‑preloaded bolts)
\( f_{ub} \) – bolt ultimate tensile strength (MPa)
\( A_s \) – tensile stress area of the bolt (mm²)
\( \gamma_{M2} \) – partial factor for bolt resistance (usually 1.25)

For double shear, the resistance is multiplied by the number of shear planes.

3. Bolt tension resistance (clause 3.6)

For a bolt in tension: \[ N_{Rd} = \frac{0.9 \, f_{ub} \, A_s}{\gamma_{M2}} \]

4. Combined shear and tension

When both shear and tension act on the same bolt, Eurocode 3 requires an interaction check. A common conservative form is:

\[ \left(\frac{V_{Ed}}{V_{Rd}}\right)^2 + \left(\frac{N_{Ed}}{N_{Rd}}\right)^2 \le 1.0 \]

The calculator reports the utilisation ratio \( \eta_{V+N} = (V_{Ed}/V_{Rd})^2 + (N_{Ed}/N_{Rd})^2 \).

5. Bearing resistance of the plate (clause 3.6)

Bearing resistance depends on the plate thickness, bolt diameter, end/edge distances and the ultimate strength of the plate material:

\[ F_{b,Rd} = \frac{k_1 \, \alpha_b \, f_u \, d \, t}{\gamma_{Mb}} \] where:

\( f_u \) – plate ultimate strength (MPa)
\( d \) – bolt diameter (mm)
\( t \) – plate thickness (mm)
\( \gamma_{Mb} \) – partial factor for bearing (often 1.25)
\( k_1, \alpha_b \) – factors for end/edge distances and hole type

To keep the interface simple, this calculator uses a conservative estimate for \( k_1 \) and \( \alpha_b \) based on your input end and edge distances and assumes standard holes unless you select a slotted/oversize hole.

6. Slip resistance for preloaded (HSFG) bolts (clause 3.9)

For slip‑resistant connections at the ultimate or serviceability limit state:

\[ F_{sl,Rd} = \frac{k_s \, n_e \, \mu \, F_{p,C}}{\gamma_{M3}} \] where:

\( k_s \) – hole factor (1.0 for normal holes, < 1.0 for slotted/oversize)
\( n_e \) – number of effective friction surfaces
\( \mu \) – slip factor (typically 0.2–0.5)
\( F_{p,C} \) – bolt preload (taken as 0.7·f_ub·A_s)
\( \gamma_{M3} \) – partial factor for slip resistance (1.25 at ULS, 1.10 at SLS)

7. Interpreting the results

Utilisation < 1.0 → the check is satisfied.
Utilisation ≈ 1.0 → the connection is at its design capacity.
Utilisation > 1.0 → increase bolt size/number, plate thickness, or improve geometry.

Limitations and good practice

Block shear, net‑section rupture and prying forces are not checked and should be verified separately.
The tool assumes uniform force distribution among bolts in the critical row.
For complex joints (e.g. moment end‑plates, eccentric connections), a full Eurocode 3 joint model is required.
Always cross‑check against the latest national annex and project‑specific requirements.

Frequently asked questions

Can I use this calculator for both lap joints and end‑plate connections?

Yes. For the purposes of bolt resistance, both are treated as bolts in single or double shear with given plate thickness and geometry. However, moment‑resisting end‑plate joints require additional checks (e.g. prying forces, plate bending) that are beyond this simplified tool.

How should I choose the slip factor μ?

The slip factor depends on the surface preparation class (e.g. blast‑cleaned, coated, as‑rolled). Typical values are given in EN 1090‑2 and national annexes. If in doubt, use a conservative value (e.g. μ = 0.30) or consult the steelwork specification for your project.

What partial factors should I use?

Default values commonly used with Eurocode 3 are:

γ_M2 = 1.25 for bolt shear and tension resistance
γ_Mb = 1.25 for bearing resistance
γ_M3 = 1.25 for slip resistance at ULS, 1.10 at SLS

Always verify these against the applicable national annex and project design basis.

Is this calculator suitable for fatigue design?

No. Fatigue design of bolted connections requires additional checks on stress ranges, detail categories and number of cycles according to EN 1993‑1‑9. This tool is intended for static (non‑fatigue) design only.