Canadian Bolt Torque Chart — A325M and A490M Bolt Torque-Tension Values

Complete reference for bolt pretension and torque values per CSA S16-19 for A325M and A490M structural bolts. M16 to M36 torque-tension relationships, turn-of-nut method, calibrated wrench method, and installation requirements for Canadian slip-critical connections.

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CSA S16 Pretension Requirements

Per CSA S16-19 Clause 22.1, bolts in slip-critical connections must be installed to a minimum pretension (clamping force). The required pretension Tb is:

Tb = 0.70 × Fu × Ab (for A325M bolts) Tb = 0.70 × Fu × Ab (for A490M bolts)

Where:

• Fu = minimum tensile strength (830 MPa for A325M, 1035 MPa for A490M)
• Ab = nominal bolt area (mm^2)

Complete Bolt Torque-Tension Table

A325M Bolts (Fu = 830 MPa, K = 0.20 typical for as-received condition)

Note: Torque = K × D × Tb where D = bolt diameter (m), Tb = pretension (N), K = nut factor.

A490M Bolts (Fu = 1035 MPa, K = 0.22 typical — higher due to higher clamping force)

Nut Factor K

The nut factor K varies with bolt condition:

Per CSA S16 and RCSC Specification, the nut factor must be verified by calibration test for each bolt lot and condition combination. A minimum of three bolt-washer-nut assemblies must be tested in a skidmore-wilhelm calibrator.

Installation Methods

Per CSA S16-19 Clause 22.2, three methods are permitted:

Method 1 — Turn of Nut

Procedure: Snug-tight condition (by impact wrench or spud wrench) → mark nut position → apply specified rotation.

Method 2 — Calibrated Wrench

Procedure: Calibrate torque wrench daily using a bolt tension calibrator (skidmore-wilhelm). Set torque to produce 5-10% above specified pretension to account for relaxation and wrench variability.

Calibration frequency: Per RCSC, every 20 bolts or at the start of each shift, whichever is less.

Method 3 — Direct Tension Indicator (DTI)

Use ASTM F959 washers with controlled protrusions that flatten at specified pretension:

• A325M bolts: Use DTI washers on the nut side
• A490M bolts: Use DTI washers on the nut side
• Gap acceptance: 0.40 mm feeler gauge should not enter at any point

Slip-Critical Connection Pretension Check

Per CSA S16 Clause 22.2, the bolt installation must achieve the specified pretension before slip resistance is considered effective:

Factored slip resistance: Vs = 0.53 × phi_s × k_s × n × Tb

Where:

• phi_s = 0.80 (resistance factor for slip resistance as of CSA S16-19 update)
• k_s = slip coefficient (0.33 for Class A, 0.50 for Class B, 0.40 for Class C)
• n = number of slip planes
• Tb = bolt pretension (N)

Minimum Pretension Check

Field verification per RCSC: Using a torque wrench, check that 10% of bolts (min 3 per connection) are tensioned to at least the specified minimum. The torque required to produce this pretension must be documented for each bolt lot.

Worked Example — M24 A325M Bolt

Given: M24 A325M bolt in slip-critical connection, as-received condition (K=0.20).

Step 1 — Pretension: Tb = 0.70 × 830 × 452 = 262,612 N = 262.6 kN

Step 2 — Installation torque: T = K × D × Tb = 0.20 × 0.024 × 262,612 = 1261 N·m

Step 3 — Verification: Using turn-of-nut method for L ≤ 4D: 1/3 turn after snug-tight

Result: Torque 1261 N·m or 1/3 turn after snug-tight.

Frequently Asked Questions

What torque is required for an M24 A325M bolt in a slip-critical connection? For an M24 A325M bolt in as-received condition (K=0.20), the required pretension is Tb = 262.6 kN, requiring approximately 1261 N·m installation torque. The range for K=0.17 to K=0.23 is 1072-1450 N·m. Always verify the actual nut factor by calibration test per RCSC.

What is the difference between snug-tight and pretensioned in CSA S16? Snug-tight is the tightness achieved by a few impacts of an impact wrench or the full effort of a person using a spud wrench — this brings the plies into firm contact but does not achieve specified pretension. Pretensioned means the bolt is tightened to a minimum of 70% of Fu × Ab per CSA S16 Clause 22.1. Snug-tight is acceptable for bearing-type connections; pretensioned is mandatory for slip-critical connections.

Can A490M bolts be installed using the turn-of-nut method? Yes, but with larger rotation requirements than A325M. For A490M with grip ≤ 4D: 1/2 turn (180°) vs 1/3 turn (120°) for A325M. The larger rotation for A490M is needed because A490M has higher strength and requires more rotation to reach the higher pretension without relaxation issues.

How is nut factor K determined for Canadian bolt installations? K is determined by calibration test in a bolt tension calibrator (Skidmore-Wilhelm). A minimum of three bolt-washer-nut assemblies from the production lot are tested. The average K is calculated from the measured torque and tension: K = T/(D×Tb). The RCSC specification requires that the calibrated K is used for setting the torque wrench.

Related Pages

• CSA Bolt Capacity — A325M & A490M Tables
• CSA Bolt Pretension — S16 Required Clamping
• Canadian Steel Bolting — A325M Fasteners
• CSA S16 Bolt Spacing & Edge Distance
• Bolt Torque Calculator
• Bolted Connection Calculator
• All Canadian References

This page is for educational reference. Torque-tension data per CSA S16-19 and RCSC Specification. Verify nut factor by calibration test. Bolt installation per CSA S16 Clause 22. Results are PRELIMINARY — NOT FOR CONSTRUCTION without independent PE/SE verification.

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