EN 1993 Bolt Torque Chart — 8.8/10.9 Torque-Tension Table M12-M36

Complete torque-tension reference for European structural bolts per EN 1993-1-8 and EN 1990. Pretension forces, tightening torques, and installation requirements for property classes 8.8 and 10.9, diameters M12 through M36.

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Bolt Property Classes — EN ISO 898-1

For structural connections in EN 1993-1-8, 8.8 and 10.9 are the standard choices.

Pretension Forces per EN 1993-1-8

The design pretension force F_p,C for bolted connections is:

F_p,C = 0.7 × f_ub × A_s

Where f_ub is the ultimate tensile strength and A_s is the tensile stress area.

Tightening Torque Values

For torque-controlled tightening, the tightening torque T is approximately:

T = k × d × F_p,C

Where k is the nut factor (0.15-0.25 depending on lubrication and surface condition) and d is the nominal bolt diameter in meters.

Recommended Tightening Torques (k = 0.20)

Note: These torque values assume k = 0.20 (as-supplied condition, slightly oiled). For specific surface conditions, apply correction factors:

Direct Tension Method

The alternative to torque-controlled tightening is the combined method per EN 1090-2:

1. Snug-tight: Tighten to the point where the connected plies are in firm contact
2. Prescribed rotation: Apply additional rotation per EN 1090-2 Table 18:
   • 90° for general installation
   • 180° for specific preloaded connections

The direct tension method (using a hydraulic tensioner or torque wrench with calibrated friction) is preferred for connections where the pretension force must be accurately controlled, such as slip-resistant connections.

Installation Methods per EN 1090-2

EN 1090-2 requires the following for preloaded bolts:

Design Applications

Common Design Scenarios

This reference covers structural design scenarios commonly encountered in structural steel design practice:

• Strength verification: Check member or connection capacity against factored loads per the applicable design code
• Serviceability checks: Verify deflections, vibrations, and other serviceability criteria
• Code compliance: Ensure design meets all provisions of the governing standard
• Connection detailing: Verify weld sizes, bolt quantities, and edge distances

Related Design Considerations

• System behavior: consider the interaction between members and connections
• Load paths: verify that forces can be transferred through the structure to the foundations
• Constructability: check that the design can be fabricated and erected practically
• Cost optimization: evaluate alternative sections or connection types for economy

Worked Example

Problem: Verify a typical steel member for the following conditions:

Typical span: 6.0 m | Load: service loads per applicable code | Section: common section in this category

Design Check:

1. Determine governing load combination (LRFD or ASD per applicable code)
2. Calculate maximum internal forces (moment, shear, axial)
3. Compute nominal capacity per code provisions
4. Apply resistance/safety factors
5. Verify interaction if combined forces exist

Result: Use the results from the Steel Calculator tool to verify design adequacy.

Frequently Asked Questions

What Australian Standard governs structural steel design?

AS 4100-2020 (Steel Structures) is the primary standard for structural steel design in Australia. It covers all aspects of design including member capacity, connections, serviceability, and fire resistance. The standard uses a limit states design philosophy with resistance factors (φ) applied to nominal capacities. Companion standards include AS/NZS 3679.1 for hot-rolled sections, AS/NZS 1554 for welding, and AS/NZS 4600 for cold-formed steel.

What are the common steel grades used in Australian construction?

The most common steel grades for Australian construction are Grade 300 and Grade 350 per AS/NZS 3679.1. Grade 300 (minimum yield 300 MPa for sections > 12 mm thick) is the standard for general structural applications. Grade 350 (minimum yield 340 MPa for sections > 12 mm) is used where higher strength reduces weight. Grade 400 and Grade 450 are available for specialized applications requiring higher strength-to-weight ratios.

How does AS 4100 compare to AISC 360?

Both AS 4100 and AISC 360 use limit states design (LRFD) principles. Key differences include: AS 4100 uses a single "capacity factor" φ approach rather than separate φ for different failure modes; AS 4100 specifies distinct buckling curves for hot-rolled and welded sections; the moment capacity formula in AS 4100 uses αm factor directly rather than Cb; and AS 4100 has more detailed provisions for slender sections and combined actions. Despite philosophical differences, both codes produce similar results for typical members.

Frequently Asked Questions

What is the difference between 8.8 and 10.9 bolts for European structural connections?

8.8 bolts (f_ub = 800 MPa, f_yb = 640 MPa) are the standard for most EN 1993-1-8 connections. 10.9 bolts (f_ub = 1000 MPa, f_yb = 900 MPa) provide 25% higher pretension and are used for high-strength connections, especially slip-resistant joints, where fewer or smaller bolts are desired. Both are quenched and tempered.

What tightening torque should I use for M20 8.8 bolts?

For M20 8.8 bolts with as-supplied condition (k = 0.20), use 549 N·m. For oiled bolts (k = 0.15), reduce to 412 N·m. Per EN 1993-1-8 Clause 3.11, the design pretension is F_p,C = 137.2 kN for M20 8.8, and torque = 0.20 × 0.020 × 137200 = 549 N·m.

Related Pages

• European Bolt Pretension — Pretension per EN 1993-1-8
• Bolt Bearing and Tearout — Bearing per EN 1993-1-8 Clause 3.6
• Bolt Group Capacity — Eccentric loads
• Bolt Spacing and Edge Distance — EN 1993-1-8 Table 3.3
• All European References

Educational reference only. Pretension per EN 1993-1-8:2005 Clause 3.11. Torque values are approximate and depend on friction conditions. Calibrate torque wrenches per EN 1090-2. Results are PRELIMINARY — NOT FOR CONSTRUCTION without independent verification.

Design Resources

Calculator tools

• Bolt Torque Calculator
• Bolted Connection Calculator
• Splice Connection Calculator
• Steel Bolted Connection Calculator

Design guides

• Bolt Torque Worked Example
• Bolted Connection Checklist
• Bolted Connection Worked Example
• AISC Shear Tab Example
• EN 1993-1-8 Bolted Connection Worked Example