What bolt grade should I use for structural connections?

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.

What is the minimum bolt spacing and edge distance?

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.

When do I need to check bearing vs shear?

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.

How many bolts do I need for a simple beam connection?

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.

What is the difference between ordinary and preloaded bolts?

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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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.

Applied Shear Force

Total factored shear at the connection

Bolt Size

Standard structural bolt sizes

Number of Bolts

Total bolts in the group

Bolt Grade

8.8 is standard for most structural work

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 capacity: From BS EN 1993-1-8 tables for Grade 8.8/10.9
Bearing capacity: 1.0 × d × t × fu / γM2 per bolt
Group capacity: Single bolt capacity × number of bolts

Frequently Asked Questions

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Last updated: March 2026

All calculations are estimates. Verify with your supplier.