Canadian Bolt Grades — CSA S16 & CSA G40.20 Guide

Bolt grades for structural steel construction in Canada follow ASTM A325 (now ASTM F3125 Grade A325) and ASTM A490 (Grade A490) as adopted by CSA S16:19 Clause 22.3. Canadian practice closely follows US bolt classifications but with Canadian-specific material standards and nominal bolt diameters in imperial units.

Bolt Grade Mechanical Properties

Bolt Grade Applications

A325 (Grade 8.8 equivalent): The standard bolt grade for most structural connections per CSA S16. Used for bearing-type connections (threads included or excluded) and slip-critical connections. Readily available, cost-effective, and suitable for galvanizing.

A490 (Grade 10.9 equivalent): Higher strength bolts used where space or bolt count is constrained. Not recommended for galvanizing due to hydrogen embrittlement risk. Must be installed with hardened washers per CSA S16 Clause 22.3.5.

CSA S16 Design Capacities — Factored (phi = 0.80)

Note: A325 fu = 830 MPa for bolts ≤ 1", 725 MPa for > 1". Shear threads out uses body area Ab; shear threads in uses tensile area At.

Worked Example: Bolt Selection

Problem: Select the number of 3/4" A325 bolts (threads included) required for a bracket connection with factored shear Vf* = 350 kN per CSA S16.

Solution:

1. From table: phi Vfn (3/4" A325, threads included) = 88.3 kN per bolt
2. Number required: n = 350 / 88.3 = 3.96 → use 4 bolts
3. Check spacing: 4 bolts at 3" spacing = 9" bolt group length — OK for typical connection

Design Resources

• Canadian Steel Grades
• Canadian Steel Properties
• Canadian CSA Bolt Capacity
• CSA S16 Beam Design
• All Canadian References

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 bolt grades are used in Canadian steel construction? CSA S16:19 references ASTM A325 and A490 bolts (now consolidated under ASTM F3125 Grades A325 and A490). Grade A325 (fub = 830 MPa for diameters ≤ 1") is the standard for most structural connections. Grade A490 (fub = 1040 MPa) is used where higher strength is needed but is not suitable for all environments.

What is the capacity factor for bolts per CSA S16? CSA S16:19 Clause 13.11 specifies phi = 0.80 for bolt shear and tension. This applies to both A325 and A490 bolts. The factored resistance is phi times the nominal resistance per bolt.

How does CSA S16 handle slip-critical connections? Per CSA S16 Clause 22.3.6, slip-critical connections are required for connections subject to fatigue, reversal of load, or where slip would cause unacceptable deformation. The slip resistance is determined by the bolt pretension (70% of minimum tensile strength per turn-of-nut method) multiplied by the slip coefficient for the faying surface condition (typically 0.33 for clean mill scale, 0.50 for blast-cleaned).

Educational reference only. Verify all values against the current edition of CSA S16:19. This information does not constitute professional engineering advice. Always consult a qualified structural engineer.