EN 1993-1-8 Bolt Capacity — Shear Fv,Rd and Tension Ft,Rd Tables for M12-M36
Complete reference for bolt shear and tension capacity in European steel design per EN 1993-1-8:2005 Clause 3.6.1 and Table 3.4. Design resistance tables for Class 8.8 and Class 10.9 bolts from M12 to M36. Includes bearing resistance (Fb,Rd), combined shear and tension interaction, and worked calculation examples with gamma_M2 = 1.25.
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EN 1993-1-8 Bolt Resistance — Design Formulas
EN 1993-1-8 Clause 3.6.1 defines the design shear and tension resistance of individual fasteners. All design values include the partial factor gamma_M2 = 1.25 for bolts.
Design Shear Resistance — Fv,Rd
Per shear plane:
Fv,Rd = alpha_v x fub x A / gamma_M2
Where:
- alpha_v = 0.60 for Classes 4.6, 5.6, 8.8; alpha_v = 0.50 for Class 10.9 (Table 3.4)
- fub = ultimate tensile strength of the bolt (800 MPa for 8.8; 1000 MPa for 10.9)
- A = tensile stress area As if the shear plane passes through the threaded portion; or the gross cross-section A = pi x d^2/4 if the shear plane passes through the unthreaded shank
- gamma_M2 = 1.25 (UK National Annex value, consistent with main text)
Design Tension Resistance — Ft,Rd
Ft,Rd = k2 x fub x As / gamma_M2
Where:
- k2 = 0.63 for countersunk bolts; 0.90 for all other bolts (Table 3.4)
- As = tensile stress area of the bolt
- gamma_M2 = 1.25
Punching Shear Resistance — Bp,Rd
Bp,Rd = 0.6 x pi x dm x tp x fu / gamma_M2
Where:
- dm = mean of across-flats and across-corners dimensions of the nut (or bolt head)
- tp = plate thickness under the bolt head or nut
- Applicable only when the plate is thin relative to the bolt size — typically tp < d/2.5
Class 8.8 Bolt Capacity Tables (fub = 800 MPa, gamma_M2 = 1.25)
All values are factored (design values) and assume:
- Threads in shear plane for Fv,Rd (conservative for most structural connections)
- Non-countersunk bolts (k2 = 0.90)
- gamma_M2 = 1.25
| Bolt Size | As (mm2) | Abody (mm2) | Fv,Rd threads (kN) | Fv,Rd shank (kN) | Ft,Rd (kN) |
|---|---|---|---|---|---|
| M12 | 84.3 | 113 | 16.2 | 21.7 | 48.6 |
| M16 | 157 | 201 | 30.1 | 38.6 | 90.4 |
| M20 | 245 | 314 | 47.0 | 60.3 | 141.1 |
| M22 | 303 | 380 | 58.2 | 73.0 | 174.5 |
| M24 | 353 | 452 | 67.8 | 86.8 | 203.3 |
| M27 | 459 | 573 | 88.1 | 110.0 | 264.4 |
| M30 | 561 | 707 | 107.7 | 135.7 | 323.1 |
| M36 | 817 | 1018 | 156.9 | 195.5 | 470.6 |
Fv,Rd threads assumes the shear plane passes through the threaded portion (alphav x fub x As / gamma_M2). _Fv,Rd shank assumes the shear plane passes through the unthreaded shank (alpha_v x fub x Abody / gamma_M2). This is the design shear resistance per shear plane — double the value for double-shear connections.
Class 10.9 Bolt Capacity Tables (fub = 1000 MPa, gamma_M2 = 1.25)
| Bolt Size | As (mm2) | Abody (mm2) | Fv,Rd threads (kN) | Fv,Rd shank (kN) | Ft,Rd (kN) |
|---|---|---|---|---|---|
| M12 | 84.3 | 113 | 16.9 | 22.6 | 60.7 |
| M16 | 157 | 201 | 31.4 | 40.2 | 113.0 |
| M20 | 245 | 314 | 49.0 | 62.8 | 176.4 |
| M22 | 303 | 380 | 60.6 | 76.0 | 218.2 |
| M24 | 353 | 452 | 70.6 | 90.4 | 254.2 |
| M27 | 459 | 573 | 91.8 | 114.6 | 330.5 |
| M30 | 561 | 707 | 112.2 | 141.4 | 403.9 |
| M36 | 817 | 1018 | 163.4 | 203.6 | 588.2 |
Note: For Class 10.9, alpha_v = 0.50 (reduced from 0.60 for 8.8). This means the shear resistance per MPa of fub is lower for 10.9 than for 8.8. The net gain going from 8.8 to 10.9 in shear (threads in plane) is only approximately 4% because the 25% increase in fub is largely offset by the alpha_v reduction from 0.60 to 0.50.
Bearing Resistance of Connected Plates — Fb,Rd
Per EN 1993-1-8 Table 3.4, the bearing resistance of the connected plate material is:
Fb,Rd = k1 x alpha_b x fu x d x t / gamma_M2
Where:
| Parameter | Description |
|---|---|
| alpha_b | = min(e1/(3d0), p1/(3d0) - 1/4, fub/fu, 1.0) for end bolts |
| alpha_b | = min(p1/(3d0) - 1/4, fub/fu, 1.0) for inner bolts |
| k1 | = min(2.8 e2/d0 - 1.7, 2.5) for edge bolts; min(1.4 p2/d0 - 1.7, 2.5) for inner bolts |
| d | = bolt diameter (not hole diameter) |
| t | = minimum connected plate thickness |
| fu | = tensile strength of the plate material |
| gamma_M2 | = 1.25 |
Bearing Capacity per mm Plate Thickness — S355 Plate (fu = 470 MPa min)
Standard bolt spacing: e1 = 40 mm, p1 = 70 mm, d0 = d + 2 mm.
| Bolt Size | alpha_b | k1 (edge bolt) | k1 (inner bolt) | Fb,Rd per mm (kN/mm) |
|---|---|---|---|---|
| M12 | 0.641 | 2.50 | 2.50 | 28.9 |
| M16 | 0.606 | 2.50 | 2.50 | 36.5 |
| M20 | 0.606 | 2.50 | 2.50 | 45.7 |
| M24 | 0.606 | 2.50 | 2.50 | 54.8 |
| M27 | 0.594 | 2.50 | 2.50 | 60.4 |
| M30 | 0.594 | 2.50 | 2.50 | 67.1 |
| M36 | 0.583 | 2.50 | 2.50 | 79.0 |
For a 10 mm thick S355 plate with M20 bolts: Fb,Rd = 45.7 x 10 = 457 kN per bolt. This exceeds the bolt shear capacity (Fv,Rd = 47.0 kN for threads in plane), so the bolt shear governs the connection design — which is the typical design intent.
Combined Shear and Tension — EN 1993-1-8 Table 3.4
When a bolt is subject to combined shear and tension, the following interaction check applies:
Fv,Ed / Fv,Rd + Ft,Ed / (1.4 x Ft,Rd) <= 1.0
This is a linear interaction, unlike the quadratic interaction used in AISC and AS 4100. The factor 1.4 accounts for the beneficial effect of tension in reducing the shear demand on the bolt shank (through friction at the faying surfaces). EN 1993-1-8 uses a simplified linear check rather than a quadratic one because the reduction in shear due to tension is explicitly quantified.
Worked Example 1: Simple Shear Connection
Problem: A fin plate connection uses 4 x M20 Class 8.8 bolts in single shear. Threads are in the shear plane. Determine the bolt group shear resistance.
Solution:
- Per bolt shear resistance (threads in plane): Fv,Rd = 47.0 kN
- Number of bolts: 4
- Bolt group shear resistance: V_Rd = 4 x 47.0 = 188.0 kN
Bearing check (S355 plate, t = 10 mm): Fb,Rd = 45.7 x 10 = 457 kN per bolt >> 47.0 kN — shear governs, as intended.
Worked Example 2: Tension Connection
Problem: An end plate moment connection uses 8 x M24 Class 8.8 bolts in the tension zone (two rows of 4 bolts). Determine the tension resistance of the bolt group.
Solution:
- Per bolt tension resistance: Ft,Rd = 203.3 kN
- Number of effective bolts in tension: 8
- Bolt group tension resistance: N_Rd = 8 x 203.3 = 1626.4 kN
This tension resistance must be checked against the applied lever arm in the moment connection, considering the compression centre and prying forces per EN 1993-1-8 Clause 6.2.4.
Worked Example 3: Combined Shear and Tension
Problem: A bracket connection has a single M20 Class 8.8 bolt subject to V_Ed = 30 kN shear and Ft_Ed = 60 kN tension. Check adequacy.
Solution:
- Fv,Rd = 47.0 kN; Ft,Rd = 141.1 kN
- Interaction: 30.0 / 47.0 + 60.0 / (1.4 x 141.1) = 0.638 + 0.304 = 0.942
- 0.942 < 1.0 — the bolt is adequate (94.2% utilisation)
Frequently Asked Questions
How is bolt shear resistance calculated per EN 1993-1-8? Fv,Rd = alpha_v x fub x A / gamma_M2, where alpha_v = 0.60 for 8.8 bolts (0.50 for 10.9), fub is the bolt tensile strength, A is the tensile stress area (threads in shear plane) or body area (shank in shear plane), and gamma_M2 = 1.25. For standard M20 Class 8.8 with threads in the shear plane: Fv,Rd = 0.60 x 800 x 245 / 1.25 = 47.0 kN. This is the resistance per shear plane — double for double-shear.
Why is alpha_v reduced to 0.50 for Class 10.9 bolts? EN 1993-1-8 reduces alpha_v from 0.60 (Classes 4.6, 5.6, 8.8) to 0.50 for Class 10.9 bolts to account for their lower ductility. Class 10.9 bolts have minimum elongation of 9% compared to 12% for 8.8. In bolted shear connections, ductility is essential for load redistribution among bolts in a group. The reduced alpha_v penalises the more brittle 10.9 material, but the 25% higher fub (1000 vs 800 MPa) still provides a modest net increase in shear resistance.
How does the combined shear and tension check differ between EN 1993-1-8 and AISC? EN 1993-1-8 uses a linear interaction: Fv,Ed/Fv,Rd + Ft,Ed/(1.4 x Ft,Rd) <= 1.0. AISC 360 uses a quadratic interaction: (Vr/Vc)^2 + (Tr/Tc)^2 <= 1.0. The EN 1993-1-8 check is more generous in combined loading because the factor 1.4 amplifies the available tension resistance when shear is also present. The EN approach accounts for friction at the faying surfaces reducing the shear demand, while the AISC quadratic approach is geometry-independent.
What partial factor gamma_M2 applies to bolt resistance calculations? gamma_M2 = 1.25 applies to all bolt resistance checks (shear, tension, bearing, and combined) in EN 1993-1-8. This is the standard value in the main text of EN 1993-1-8 and is adopted by the UK, German, and most other National Annexes. Some national annexes may modify gamma_M2 — always check the relevant NA for your jurisdiction. Note that gamma_M2 = 1.25 also applies to net section rupture and weld resistance, making it a consistent value for all fracture-governed failure modes in EN 1993.
What is the design tension resistance of an M24 Class 10.9 bolt? Ft,Rd = k2 x fub x As / gamma_M2 = 0.90 x 1000 x 353 / 1.25 = 254.2 kN. This is approximately 25% higher than the equivalent Class 8.8 bolt (203.3 kN), reflecting the proportional increase in fub. The tension resistance uses the tensile stress area As regardless of the shear plane position, because the threaded portion is always present in the tension load path. For preloaded bolts (Categories D and E), the tension resistance is Ft,Rd but must also be checked against the preload force to ensure the bolt is not over-tensioned at ULS.
Related Pages
- EN 1993-1-8 Connection Design Guide — Bolt categories, welds, joint classification
- EN 1993-1-8 Bolt Grades — 4.6, 5.6, 8.8, 10.9 mechanical properties
- EN 1993-1-8 Bolt Hole Sizes — Clearance, oversized, slotted holes
- EN 1993-1-8 Bolt Pretension — Slip-resistant Cat B/C, Fp,Cd
- EN 1993-1-1 Beam Design Guide — Mc,Rd, Vc,Rd, LTB
- European Steel Properties — EN 10025 S235-S460 Fy and Fu
- Bolted Connections Calculator
- Beam Capacity Calculator
- Column Capacity Calculator
Educational reference only. All capacity values are per EN 1993-1-8:2005 and assume gamma_M2 = 1.25 (UK NA value). Verify all values against the current edition of the Eurocode and the applicable National Annex for your project jurisdiction. Bolt resistances are for a single bolt per shear plane; multiply for multiple bolts and double-shear configurations. Results are PRELIMINARY — NOT FOR CONSTRUCTION. All designs must be independently verified by a licensed Professional Engineer or Chartered Structural Engineer.