CSA Bolt Capacity — A325M & A490M Shear and Tension Tables per CSA S16-19

Complete reference for bolt shear and tension capacities per CSA S16-19 Clause 13.12. Metric bolt capacities for A325M and A490M bolts from M16 to M36, with separate values for threads intercepted (AA) and threads excluded (AX) in the shear plane.

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CSA S16 Bolt Design Philosophy

CSA S16-19 uses limit states design for bolted connections under Clause 13.12. The factored resistance of a bolt in shear or tension is determined using:

Resistance factor: phi_b = 0.80 (bolts in bearing-type connections)

This is slightly higher than the AISC 360 phi = 0.75 for bolts. The difference reflects the Canadian calibration of resistance factors to match the target reliability index (beta = 3.0 for connections).

Bolt Shear Resistance

Per CSA S16-19 Clause 13.12.1.2:

Shear resistance (threads excluded from shear plane — AX): Vr = 0.60 _ phi_b _ phi*ax * Ab _ Fu

Where:

• phi_b = 0.80
• phi_ax = 0.80 (AX factor, threads excluded)
• Ab = nominal bolt body area = pi * d^2 / 4
• Fu = minimum tensile strength of bolt (830 MPa for A325M, 1035 MPa for A490M)

Shear resistance (threads intercepted in shear plane — AA): Vr = 0.60 _ phi_b _ phi*aa * Ab _ Fu

Where phi_aa = 0.65 for threads intercepted (reduced area through threads).

These equations simplify to the tabulated values in CSA S16-19 Table 2.

Complete Bolt Capacity Table — A325M

A325M bolts: Fu = 830 MPa minimum. Ab = nominal body area for the designated bolt diameter.

A325M Bolt Calculations

For M24 A325M bolt (AX — threads excluded from shear plane):

Ab = pi * 24^2 / 4 = 452.4 mm^2

Vr = 0.60 _ 0.80 _ 0.80 _ 452.4 _ 830 / 1000 = 0.60 _ 0.80 _ 0.80 _ 452.4 _ 830 / 1000 = 143.9 kN

For M24 A325M bolt (AA — threads intercepted in shear plane):

Vr = 0.60 _ 0.80 _ 0.65 _ 452.4 _ 830 / 1000 = 117.0 kN

Tension resistance (same for AA and AX):

Tr = 0.75 _ phi_b _ Ab _ Fu = 0.75 _ 0.80 _ 452.4 _ 830 / 1000 = 240.4 kN

Note: the 0.75 factor accounts for the reduced tensile area through the threaded portion, and phi_b = 0.80 is the resistance factor for bolts.

Complete Bolt Capacity Table — A490M

A490M bolts: Fu = 1035 MPa minimum.

A490M Bolt Calculations

For M24 A490M bolt (AX):

Vr = 0.60 _ 0.80 _ 0.80 _ 452.4 _ 1035 / 1000 = 179.5 kN

For M24 A490M bolt (AA):

Vr = 0.60 _ 0.80 _ 0.65 _ 452.4 _ 1035 / 1000 = 139.0 kN

Tension resistance:

Tr = 0.75 _ 0.80 _ 452.4 * 1035 / 1000 = 299.9 kN

Thread Condition Effects — AA vs AX

The ratio of AA to AX capacity is constant for all bolt sizes:

AA/AX = 0.65 / 0.80 = 0.8125

For A325M M20 bolts:

• Vr (AX) = 100.0 kN
• Vr (AA) = 81.3 kN
• AA/AX = 0.813

This means a bolt with threads in the shear plane has approximately 19% less shear resistance than a bolt with threads excluded from the shear plane. Designers should specify bolt lengths that position the threaded portion outside the shear plane (AX condition) to maximise connection capacity.

Practical Guidance on Thread Condition

Combined Shear and Tension

Per CSA S16-19 Clause 13.12.4, bolts subject to combined shear and tension must satisfy:

(Vf / Vr)^2 + (Tf / Tr)^2 <= 1.0

This interaction equation is identical to the AISC 360 approach. The factored shear force Vf and factored tension force Tf are combined in an elliptical interaction.

Worked Example — Combined Shear and Tension

Problem: An M24 A325M bolt in a beam-to-column moment end plate connection is subject to Vf = 60 kN (shear) and Tf = 100 kN (tension due to prying action). Threads are excluded from the shear plane (AX). Check the bolt.

Given:

• M24 A325M: Vr (AX) = 143.9 kN, Tr = 240.4 kN
• Check interaction: (60/143.9)^2 + (100/240.4)^2 <= 1.0

Calculation:

• (60/143.9)^2 = (0.417)^2 = 0.174
• (100/240.4)^2 = (0.416)^2 = 0.173
• Sum = 0.174 + 0.173 = 0.347 <= 1.0

Result: Bolt adequate. Using 54% of shear capacity and 42% of tension capacity separately, the combined interaction ratio is only 0.35 due to the elliptical interaction.

Bearing Resistance

Per CSA S16-19 Clause 13.11.2, the bearing resistance of connected parts (not the bolt) is:

Br = 3.0 _ phi_br _ t _ d_hole _ Fu

Where:

• phi_br = 0.80 (resistance factor for bearing)
• t = thickness of the connected part (mm)
• d_hole = hole diameter (mm, actual hole dimension)
• Fu = tensile strength of the connected part (MPa)

Bearing Resistance for Common Plate Thicknesses

For CSA G40.21 350W plates (Fu = 450 MPa) with M20 standard holes (22 mm):

For standard structural plate thickness (6-25 mm) in 350W steel with M20 A325M bolts, bearing resistance rarely governs because CSA S16's factor of 3.0 on the bearing equation provides significant capacity. Table 5-4 in the CISC Handbook confirms that bolt shear governs for nearly all practical combinations.

Bearing at End Holes

For bolts near the edge of the connected part, the bearing resistance is limited by tear-out:

Br*tearout = phi_br * t _ e * Fu

Where e = distance from the centre of the hole to the edge of the part in the direction of the applied load. This linear tear-out check applies when edge distances are less than the full bearing development distance.

Bolt Group Capacity

For bolt groups subjected to eccentric shear, CSA S16-19 does not prescribe a specific analysis method. The CISC Handbook uses the instantaneous centre of rotation method (elastic or plastic), consistent with AISC's approach. The CISC Handbook Part 5 provides eccentric load tables (C-values) for common bolt patterns.

For a bolt group with n bolts subjected to concentric shear:

Total Vr_group = n * Vr (per bolt, all bolts assumed equal)

For eccentric loading, the instantaneous centre method distributes load unequally, and the effective number of bolts is less than n. The C-value from CISC Handbook Table 5-1 to 5-6 accounts for eccentricity and geometry.

Frequently Asked Questions

What is the difference between threads excluded (AX) and threads intercepted (AA) in CSA S16 bolt design? Threads excluded (AX) means the threaded portion of the bolt is outside the shear plane(s), so the full body area Ab resists shear. Threads intercepted (AA) means one or more threads lie in the shear plane, reducing the effective area. CSA S16-19 Clause 13.12.1.2 uses phi_ax = 0.80 for AX and phi_aa = 0.65 for AA. The AA capacity is approximately 81% of the AX capacity. Proper bolt length selection should target the AX condition for maximum efficiency.

What is the shear capacity of an M24 A325M bolt in a bearing-type connection per CSA S16? For M24 A325M with threads excluded from shear plane (AX): Vr = 143.9 kN. With threads intercepted (AA): Vr = 117.0 kN. The values come from CSA S16-19 Table 2 using phi_b = 0.80, Fu = 830 MPa for A325M bolts. For slip-critical connections, the factored slip resistance replaces shear capacity as the design limit state.

What is the difference between CSA S16 and AISC 360 bolt capacity? CSA S16 uses phib = 0.80 while AISC 360 uses phi = 0.75 for bolts in bearing. However, the underlying equations differ: CSA S16 uses 0.60 * phib * Ab * Fu for shear with additional factors for thread condition (phi_ax = 0.80, phi_aa = 0.65), while AISC 360 directly specifies different nominal stresses for threads included vs excluded. The practical result is similar capacities — a M24 A325M bolt per CSA S16 has Vr (AA) = 117.0 kN vs AISC's approximately 113 kN for a 7/8" A325 bolt. Canadian bolts are slightly more conservative for threads excluded.

How is bolt tension capacity calculated in CSA S16? Tr = 0.75 _ phi_b _ Ab _ Fu. The 0.75 factor accounts for the reduced area at the threaded portion. For A325M M20: Tr = 0.75 _ 0.80 _ 314 _ 830 / 1000 = 167.1 kN. For A490M M20: Tr = 0.75 _ 0.80 _ 314 * 1035 / 1000 = 208.4 kN. These values are for pure tension. Combined shear and tension follows the interaction equation (Vf/Vr)^2 + (Tf/Tr)^2 <= 1.0 per Clause 13.12.4.

What is the bearing resistance of a 12 mm 350W plate with M20 bolts? Br = 3.0 _ phi_br _ t _ d_hole _ Fu = 3.0 _ 0.80 _ 12 _ 22 _ 450 / 1000 = 285.1 kN per bolt. This far exceeds the M20 A325M AA shear capacity of 81.3 kN, so bearing does not govern. The bearing resistance only governs for very thin plates (t < 5 mm) or for plates with lower Fu (such as 300W with Fu = 440 MPa). For typical structural connections (t >= 8 mm), bolt shear capacity governs the connection design.

Related Pages

• CSA Bolt Hole Sizes — Standard & Oversized Holes
• CSA Bolt Pretension — S16 Required Clamping
• Canadian Steel Bolting — A325M Fasteners & CSA S16
• CSA W59 Minimum Weld Size — Fillet Weld Table
• CSA S16 Code Overview
• Bolted Connection Calculator
• Bolt Torque Calculator
• Column Capacity Calculator

This page is for educational reference. All bolt capacity data per CSA S16-19 Table 2. Verify values against the current code edition and bolt manufacturer certifications before design. Capacities shown are for bolts in bearing-type connections. For slip-critical connections, use lower slip resistance values. Results are PRELIMINARY — NOT FOR CONSTRUCTION without independent PE/SE verification.