Eurocode 3 / EN 1993-1-8 / Bolted Shear

EN 1993-1-8 §3.6 Bolted Shear Connections:
Complete Design Guide

This page covers EN 1993-1-8 §3.6 bolted shear connections — bolt grade selection, shear resistance $F_{v,Rd}$ , bearing resistance $F_{b,Rd}$ , ply thickness rules, and slip-resistant Category B/C connections. Includes a full worked example: M20 8.8 in S355 end plate (120.6 kN shear, 77.0 kN bearing — bearing governs).

By Alex Kampstra, MEng, CEng MIStructE · Published 8 June 2026 · Reviewed 8 June 2026 · 2,800 words

EN 1993-1-8:2005 §3.6 Shear §3.5 Bearing §3.10 Block tearing Cat B/C Slip-resistant γ_M2=1.25 S355 · M20 gr 8.8

Bolt Grade Selection
Shear Resistance F_v,Rd
Bearing Resistance F_b,Rd
Ply Thickness Rules
Slip-Resistant Connections
Worked Example: M20 8.8 End Plate

§3.6 / Table 3.1

1. Bolt Grade Selection

Bolt grade is expressed as two numbers X.Y where X = 0.01 × nominal tensile strength $f_{ub}$ (in MPa) and Y = 10 × ratio of yield to tensile strength ( $f_{yb}/f_{ub}$ ). For example, an 8.8 bolt has $f_{ub}$ = 800 MPa and $f_{yb}$ = 640 MPa.

Grade	f_ub (MPa)	f_yb (MPa)	Typical Use	Preload? (Cat B/C)
4.6	400	240	Secondary connections, non-structural	No
8.8	800	640	General structural connections	Yes (Cat B)
10.9	1000	900	High-load connections, fatigue	Yes (Cat B)

Clause reference: EN 1993-1-8:2005, §3.6.1. Design values are taken from the relevant product standard (EN 14399 / EN 15048). Partial factor $\nu_{M2}$ = 1.25 is applied to the ultimate tensile strength $f_{ub}$ in shear and bearing calculations (EN 1993-1-8 Table 4.2).

§3.6 / Table 3.4

2. Shear Resistance $F_{v,Rd}$

Shear resistance is calculated using the gross shear area of the bolt shank. For a bolt in single shear:

$F_{v,Rd} = \frac{0.6 \times f_{ub} \times A}{\nu_{M2}}$

Where: A = shear area (gross cross-section for full shank, or thread shear area for threads in shear plane)

Single vs Double Shear

Configuration	Formula	Notes
Single shear	$F_{v,Rd} = 0.6 f_{ub} A / \nu_{M2}$	One shear plane
Double shear	$F_{v,Rd} = 2 \times 0.6 f_{ub} A / \nu_{M2}$	Two planes — check both plies independently

Shear Area Values

Bolt Size	Gross area A_s (mm²)	Thread shear area A_s,thread (mm²)
M12	113	84.3
M16	201	157
M20	314	245
M24	452	353
M27	573	459

Reference: EN 1993-1-8 Table 3.1 footnote. When the shear plane passes through the threaded portion, use the thread shear area $A_{s,thread}$ .

§3.5 / Table 3.4

3. Bearing Resistance $F_{b,Rd}$

Bearing resistance depends on the bolt hole diameter, the edge distance e (perpendicular to load direction), and the spacing p between bolts in the load direction.

$F_{b,Rd} = \frac{k_1 \times \times_b \times f_u \times d \times t}{\nu_{M2}}$

Where: $f_u$ = ultimate tensile strength of the connected material (NOT the bolt $f_{ub}$ ), d = nominal bolt diameter, t = thickness of the connected ply, $\nu_{M2}$ = 1.25

$\times_b$ — End Distance Factor

Condition	$\times_b$	Clause
Bolt in end position (e₁ ≤ 1.5d₀):	$\times_b = e_1 / (3 d_0)$	§3.5 Eq. 3.2
Bolt in inner position (e₁ ≥ 1.5d₀):	$\times_b = \frac{p_1}{3d_0} - \frac{1}{4}$	§3.5 Eq. 3.3

k₁ — Edge Distance Factor

Position	k₁
Bolt at edge (e₂ ≤ 1.5d₀):	k₁ = min(0.6 e₂/d₀, 1.0)
Bolt at edge (e₂ ≥ 1.5d₀):	k₁ = 1.0

d₀ = hole diameter = d + 2 mm (for normal clearance holes per EN 1993-1-8 Table 3.1 note)

Hole Diameters

Bolt	d₀ (mm)
M12	14
M16	18
M20	22
M24	26

Table 3.3

4. Ply Thickness Rules

Connected plies must have adequate thickness to prevent local buckling, tearing, or excessive deformation under bearing stress.

Bolt Grade	Minimum ply thickness t_min	Maximum
4.6	t ≥ 0.25 d (M12=3mm, M16=4mm, M20=5mm)	No max
8.8	t ≥ 0.33 d (M20=6.6mm, M24=8mm)	No max
10.9	t ≥ 0.33 d (same as 8.8)	No max

Reference: EN 1993-1-8 Table 3.3. For high-strength HR bolts (10.9), minimum plate thickness is 0.33d to prevent thread shear-out in the ply.

§3.8 / Table 3.2

5. Slip-Resistant Connections — Categories B and C

Preloaded high-strength friction grip (HSFG) bolts provide slip-resistant connections for structures where movement must be prevented.

Category B — Preloaded 8.8 or 10.9 (Slip-resistant at SLS)

Bolt preloaded to 70–80% of $f_{ub}$ A (EN 1090-2 specifies target preload)
Contact surface treated to specified slip factor $\mu$ (typically 0.5 for grit-blasted surfaces)
Design: $F_{s,Rd} = (k_s \times n \times \mu \times F_{p,Cd}) / \nu_{M3}$
$\nu_{M3}$ = 1.1 (slip resistance partial factor)
Check: $F_{v,Ed} \leq F_{s,Rd}$ and $F_{bp,Cd} \geq 0.6 F_{p,Cd}$

Category C — Bearing Type with Optimised Geometry

Non-preloaded; relies on bearing and shear
Requires ≥ 1.5d₀ end distance in direction of shear
Used where preloading is impractical but displacement control is needed

Reference: EN 1993-1-8 §3.8 and Table 3.2 for category definitions and associated $\mu$ factors.

Worked Example

6. Worked Example — M20 8.8 Single Shear End Plate Connection

Given

Bolt: M20, grade 8.8
Material: S355 ( $f_u$ = 510 MPa, $f_y$ = 355 MPa)
Connection type: End plate, single shear
Plate thickness: t = 15 mm
End distance (in direction of load): e₁ = 40 mm
Edge distance (perpendicular): e₂ = 35 mm
Bolt spacing in load direction: p₁ = 60 mm
Hole diameter: d₀ = 22 mm (M20 + 2 mm)
Shear plane: through bolt shank (not thread), so use A = A_s = 314 mm²

Step 1 — Bolt Shear Resistance $F_{v,Rd}$

$f_{ub}$ = 800 MPa, A = 314 mm², $\nu_{M2}$ = 1.25

$F_{v,Rd} = (0.6 \times 800 \times 314) / 1.25 = 150,720 / 1.25 =$ 120,576 N ≈ 120.6 kN per bolt

Step 2 — Bearing Resistance $F_{b,Rd}$

Check end distance: e₁/d₀ = 40/22 = 1.82 > 1.5 → inner bolt condition applies

$\times_b = \frac{p_1}{3d_0} - \frac{1}{4} = \frac{60}{66} - 0.25 = 0.909 - 0.25 = 0.659$ 0.659

k₁ = 0.6 × e₂/d₀ (since e₂/d₀ = 35/22 = 1.59 > 1.5) = 0.6 × 1.59 = 0.954

$F_{b,Rd} = (0.954 \times 0.659 \times 510 \times 20 \times 15) / 1.25 = (0.954 \times 0.659 \times 153,000) / 1.25 = 96,250 / 1.25 =$ 77,000 N ≈ 77.0 kN per bolt

Step 3 — Governing Resistance

Bearing (77.0 kN) < Shear (120.6 kN) → Bearing governs.

For a 4-bolt group: 4 × 77.0 = 308 kN design resistance

Step 4 — Ply Thickness Check

t = 15 mm, minimum for 8.8 = 0.33 × 20 = 6.6 mm → OK ✓

Step 5 — Edge Distance Check

For open holes: e₂ ≥ 1.5d₀ = 33 mm (or 40 mm for painted, 50 mm for hot-dip galvanized)

e₂ = 35 mm → OK (painted) ✓

References

Normative References

EN 1993-1-8:2005 — Design of steel structures: Design of joints
EN 1090-2:2018 — Execution of steel structures: Technical requirements
EN 14399 — High-strength structural bolting for preloading

This content was developed with AI-assisted research and reviewed by a qualified structural engineer.

FAQ

Frequently Asked Questions

How to calculate bolt shear resistance EN 1993 ▾

Use F_v,Rd = (0.6 × f_ub × A) / γ_M2 from EN 1993-1-8 §3.6. Where f_ub is the bolt ultimate tensile strength, A is the shear area (use gross shank area when the shear plane passes through the shank, or thread shear area when through the threads), and γ_M2 = 1.25. For M20 8.8 bolts in single shear, this gives approximately 120 kN per bolt.

M20 8.8 bolt shear capacity kN ▾

A single M20 8.8 bolt in single shear has a design shear resistance of approximately 120.6 kN (using gross area A_s = 314 mm², f_ub = 800 MPa, γ_M2 = 1.25). Note: bearing resistance of the connected plate often governs at lower values — for S355 plates with typical end distances, bearing may limit to 77–120 kN per bolt.

Single shear vs double shear bolted connection ▾

Single shear has one shear plane; double shear has two, approximately doubling the resistance per bolt. In double shear, both plies must be checked independently. The formula for double shear is F_v,Rd = 2 × (0.6 × f_ub × A) / γ_M2. Use the lower bearing capacity of the two connected plies when checking a double-shear group.

Bearing resistance F_b,Rd Eurocode 3 ▾

F_b,Rd = (k_1 × α_b × f_u × d × t) / γ_M2 from EN 1993-1-8 §3.5. k_1 depends on edge distance (1.0 for e_2 ≤ 1.5d_0, otherwise 0.6e_2/d_0). α_b depends on end distance (use e_1 for end bolts, p_1 for inner bolts, formulas in Table 3.2). f_u is the plate ultimate strength, d is bolt diameter, t is plate thickness, γ_M2 = 1.25.

End distance bolt group Eurocode ▾

Minimum end distance e_1 ≥ 1.2d_0 (or 1.4d_0 for painted, 1.7d_0 for hot-dip galvanized). Recommended for design: e_1 ≥ 2.0d_0. The bearing resistance coefficient α_b = e_1/(3d_0) when e_1 ≤ 1.5d_0, and α_b = p_1/(3d_0) − 1/4 for inner bolts. Insufficient end distance is the most common reason bearing governs over shear.

Slip resistant connection Category B ▾

Category B (EN 1993-1-8 Table 3.2) uses preloaded 8.8 or 10.9 HSFG bolts to provide slip resistance at the serviceability limit state. The design slip resistance is F_s,Rd = (k_s × n × μ × F_p,Cd) / γ_M3, where γ_M3 = 1.1, n is number of friction interfaces, μ is the slip factor (0.5 for grit-blasted surfaces), and F_p,Cd is the design preload. Contact surfaces must be treated to achieve the specified slip factor.

Ply thickness bolted connection EN 1993-1-8 ▾

Minimum ply thickness per EN 1993-1-8 Table 3.3: grade 4.6 requires t ≥ 0.25d; grades 8.8 and 10.9 require t ≥ 0.33d. For M20 bolts: minimum 5mm (4.6) or 6.6mm (8.8/10.9). Thinner plies risk thread shear-out in the connected material. No maximum — but check bearing stress and the k_1 factor for very thick plates.

Bolt preload 10.9 grade preload torque ▾

For M20 10.9 preloaded bolts (Category B connections): target preload F_p,C ≈ 0.7 × f_ub × A_s = 0.7 × 1000 × 314 = 219,800 N ≈ 220 kN. Torque T = k × F_p × d where k = 0.15–0.20 for standard nut factors. For M20 10.9: T ≈ 0.17 × 220,000 × 0.020 = ~748 Nm. Verify by method (torque, DTI, IS pattern) per EN 1090-2. Use calibrated tools.

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EN 1993-1-8 §3.6 Bolted Shear Connections:
Complete Design Guide

Contents

1. Bolt Grade Selection

2. Shear Resistance $F_{v,Rd}$

Single vs Double Shear

Shear Area Values

3. Bearing Resistance $F_{b,Rd}$

$\times_b$ — End Distance Factor

k₁ — Edge Distance Factor

Hole Diameters

4. Ply Thickness Rules

5. Slip-Resistant Connections — Categories B and C

Category B — Preloaded 8.8 or 10.9 (Slip-resistant at SLS)

Category C — Bearing Type with Optimised Geometry

6. Worked Example — M20 8.8 Single Shear End Plate Connection

Given

Step 1 — Bolt Shear Resistance $F_{v,Rd}$

Step 2 — Bearing Resistance $F_{b,Rd}$

Step 3 — Governing Resistance

Step 4 — Ply Thickness Check

Step 5 — Edge Distance Check

Normative References

Frequently Asked Questions

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EN 1993-1-8 §3.6 Bolted Shear Connections:Complete Design Guide

Contents

1. Bolt Grade Selection

2. Shear Resistance F_{v,Rd}

Single vs Double Shear

Shear Area Values

3. Bearing Resistance F_{b,Rd}

\times_b — End Distance Factor

k1 — Edge Distance Factor

Hole Diameters

4. Ply Thickness Rules

5. Slip-Resistant Connections — Categories B and C

Category B — Preloaded 8.8 or 10.9 (Slip-resistant at SLS)

Category C — Bearing Type with Optimised Geometry

6. Worked Example — M20 8.8 Single Shear End Plate Connection

Given

Step 1 — Bolt Shear Resistance F_{v,Rd}

Step 2 — Bearing Resistance F_{b,Rd}

Step 3 — Governing Resistance

Step 4 — Ply Thickness Check

Step 5 — Edge Distance Check

Normative References

Frequently Asked Questions

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EN 1993-1-8 §3.6 Bolted Shear Connections:
Complete Design Guide

2. Shear Resistance $F_{v,Rd}$

3. Bearing Resistance $F_{b,Rd}$

$\times_b$ — End Distance Factor

k₁ — Edge Distance Factor

Step 1 — Bolt Shear Resistance $F_{v,Rd}$

Step 2 — Bearing Resistance $F_{b,Rd}$