Clause 10.3.3 gives the design strength of a bolt in shear and the design bearing strength of the bolt on the connected plate. The bolt capacity is the minimum of shear strength (Vdsb) and bearing strength (Vdpb). For high-strength bolts (Grade 8.8, 10.9), friction-type connections are covered in Cl. 10.4.
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Key Requirements
•Design shear strength per bolt: Vdsb = Vnsb / γmb where Vnsb = fu/(√3) × Anb (for shear plane through threads) or fu/(√3) × Asb (for shear plane through shank)
•Anb = net tensile stress area of bolt (through threads); Asb = gross shank area = π/4 × d²
•For long joints (> 15d), reduce Vdsb by factor βlj = 1 − (lj − 15d)/(200d)
•Design bearing strength: Vdpb = Vnpb / γmb where Vnpb = 2.5 × kb × d × t × fu
Design Shear Strength per Bolt — Single Shear, Thread in Shear Plane (kN)
Bolt Size
Grade 4.6
Grade 8.8
Grade 10.9
M12 (Anb = 84.3 mm²)
15.5
31.1
38.9
M16 (Anb = 157 mm²)
28.9
57.9
72.4
M20 (Anb = 245 mm²)
45.3
90.5
113.2
M22 (Anb = 303 mm²)
55.9
111.7
139.7
M24 (Anb = 353 mm²)
65.1
130.2
162.8
Vdsb = (fub/√3) × Anb / γmb. γmb = 1.25. Single shear, shear plane through threads. For double shear, multiply by 2. For shear plane through shank, use Asb instead of Anb.
Vnsb = Nominal shear capacity of bolt (N)fu_b = Ultimate tensile strength of bolt (MPa)Anb = Net tensile stress area of bolt (mm²) — for shear planes through threadsAsb = Gross shank area of bolt (mm²) — for shear planes through shankn_n = Number of shear planes through threadsn_s = Number of shear planes through shank
Nominal bearing strength of bolt on the connected plate
Vnpb = Nominal bearing capacity (N)kb = min(e/3d0, p/3d0 − 0.25, fub/fu, 1.0)d = Nominal bolt diameter (mm)t = Total thickness of connected plates in bearing (mm)fu = Ultimate tensile stress of the plate (MPa)
Practical Notes
✓M20 Grade 4.6 bolts are the default for Indian structural steelwork. Single shear capacity ≈ 45.3 kN per bolt. For a 4-bolt connection (2×2 pattern), capacity ≈ 181 kN — adequate for most secondary beams.
✓Always check bearing on the thinner plate — for a 10 mm gusset with M20 bolt (Grade 4.6, E250 plate), bearing capacity per bolt ≈ 2.5 × 1.0 × 20 × 10 × 410 / 1250 = 164 kN, which exceeds shear capacity. Shear usually governs for Grade 4.6.
✓For Grade 8.8/10.9 bolts, bearing on the plate often governs instead of bolt shear — because the bolt is much stronger but the plate bearing limit remains the same.
Common Mistakes
⚠Using Asb (shank area) when the shear plane passes through the threaded portion — most connections have threads in the shear plane, so use Anb (net area, which is ~78% of Asb).
⚠Forgetting the long joint reduction factor (βlj) for connections longer than 15d — this can reduce shear capacity by 15–20%.
⚠Not checking bearing on the thinner plate — for high-strength bolts (8.8/10.9), plate bearing often governs.