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Steel Connection Calculator — Bolt Group Capacity Check
Check bolt group capacity for shear connections per BS EN 1993-1-8. Calculates shear per bolt, bearing check, and overall utilisation for M12 to M24 bolts.
Total factored shear at the connection
Total bolts in the group
Thinnest plate in the connection
Safety notice
Steel members must be designed or checked by a structural engineer before fabrication or installation. Treat these figures as initial guidance for planning and budgeting, not a structural design.
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How We Calculate This
This calculator checks a bolt group for shear capacity and bearing capacity per BS EN 1993-1-8, ensuring the connection can safely transfer the applied shear force.
Checks performed
- Shear per bolt: Applied load ÷ number of bolts
- Bolt shear resistance (Fv,Rd): αv × fub × As / γM2 per shear plane (BS EN 1993-1-8 Table 3.4), with threads assumed in the shear plane — αv = 0.6 for Grade 8.8, αv = 0.5 for Grade 10.9, γM2 = 1.25 (UK NA)
- Bearing resistance (Fb,Rd): k₁ × αb × fu × d × t / γM2 (BS EN 1993-1-8 cl 3.6.1). This tool takes k₁ × αb = 1.0 — the conservative minimum-spacing bound; with standard SCI detailing it rises toward 2.0–2.5, so real bearing capacity is higher
- Group capacity: Single bolt resistance × number of bolts
Shear resistances use the conservative threads-in-shear-plane case (SCI P358). If the shear plane falls on the unthreaded shank, capacity is higher (αv = 0.6 on the gross area for all grades). This is a first-pass capacity check, not a full connection design — block tearing, bolt-row tension and weld/plate checks are not covered.
Frequently Asked Questions
Grade 8.8 is the standard bolt grade for structural steelwork connections in the UK. They are property class 8.8 to BS EN ISO 4014/4017 with nuts to BS EN ISO 4032. Grade 10.9 bolts have higher strength and are used for pre-loaded (friction grip) connections. Never use mild steel (Grade 4.6) bolts for structural connections.
Per BS EN 1993-1-8: minimum bolt spacing is 2.2 × hole diameter (typically 2.5d used in practice). Minimum end distance is 1.2 × hole diameter. Standard practice uses 70mm pitch for M20 bolts, 50mm for M16, with 40mm end distance. These minima prevent splitting and ensure adequate bearing capacity.
Both must always be checked. Shear failure is the bolt shearing through, while bearing failure is the bolt crushing into the plate. For thin plates (less than 10mm), bearing often governs. For thick plates with small bolts, shear governs. The connection capacity is the lower of the shear and bearing capacities.
For a standard fin plate or double cleat connection to a beam end, 2-3 bolts minimum for light beams, 4-6 for medium beams (up to about 500mm deep), and 6-10 for heavy beams. The SCI Green Book (P358) provides standard connection designs with bolt numbers for various beam sizes and load levels.
Ordinary bolts (non-preloaded) transfer load through shear and bearing — they are the standard for most connections. Preloaded bolts (formerly HSFG) are tightened to a specified preload so load is transferred by friction between the plate faces. Preloaded bolts are required for connections subject to fatigue, vibration, or where slip is unacceptable.
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Last updated: March 2026
Verified against UK standards · estimates only, confirm with your supplier.