Anchor Bolt Grades — CSA S16 / ASTM F1554

Canadian anchor bolts are most commonly ASTM F1554 Grade 36, 55, or 105:

Grade 55 is the default for Canadian commercial and industrial buildings. CSA S16 references ASTM F1554 for anchor bolt material. For seismic applications in high-seismic zones (Vancouver, Montreal), the ductility of Grade 55 is preferred over Grade 105 unless prequalification testing per CSA S16 Clause 27 demonstrates adequate performance.

Anchor Bolt Tension — CSA S16 Clause 21.1

Tension resistance of a single anchor bolt:

T_r = 0.75 times phi_b times A_b times F_u

Where:

• phi_b = 0.80 (CSA S16 for bolts)
• A_b = nominal bolt area (unthreaded shank)
• A_n = net area (threaded portion) ~0.75 times A_b for ISO metric bolts

Anchor Bolt Shear — CSA S16 Clause 21.1

Shear resistance of a single anchor bolt:

V_r = 0.60 times phi_b times A_b times F_u (threads excluded from shear plane)

For bolts with threads in the shear plane, multiply by 0.70. For base plates with grout pads (min 25 mm non-shrink grout), the shear plane passes through the threaded portion. Use the reduced shear capacity.

Concrete Breakout — CSA A23.3 Annex D

Per CSA A23.3 (harmonised with ACI 318 Annex D), the concrete breakout strength of a single anchor in tension:

N_Rd,c = (A_Nc / A_Nco) times psi_ed,N times psi_c,N times psi_cp,N times N_b

Where N_b = k_c times lambda_a times sqrt(f'_c) times h_ef^1.5 (N). k_c = 10 for cast-in headed anchors (metric, MPa units).

For C30 concrete (f'_c = 30 MPa), h_ef = 300 mm: N_b = 10 times 1.0 times sqrt(30) times 300^1.5 = 284.5 kN. With phi_c = 0.65: phi times N_b = 185 kN.

For a group of 4 anchors at 250 mm spacing: A_Nc = (250 + 1.5 times 300)^2 = 700^2 = 490,000 mm^2. A_Nco = 9 times h_ef^2 = 810,000 mm^2. Group capacity (no edge effects): N_Rd,c,group = 490,000/810,000 times 4 times 284.5 times 0.65 = 448 kN total.

Side-Face Blowout — CSA A23.3

For headed anchors near an edge (c_a1 < 0.4 times h_ef), side-face blowout must be checked:

N_sb = 13 times c_a1 times sqrt(A_brg) times sqrt(f'_c) (single anchor, metric)

Blowout governs when edge distance is small relative to embedment depth — common in foundation walls and pile caps.

Combined Shear and Tension Interaction

Per CSA S16 Clause 21.1, anchors subject to combined shear and tension must satisfy:

(T_f / T_r)^2 + (V_f / V_r)^2 <= 1.0 (elliptical interaction)

Worked Example 1 — Canadian Column Base (Compression Governs)

Problem: W310x97 column (350W), N_f = 1800 kN compression, M_f = 80 kN.m base moment in a Toronto office building. Use 4-M24 F1554-55 bolts.

Step 1 — Base Plate: 400 times 400 times 25 mm, 300W steel. Four M24 F1554-55 bolts at 300 mm gauge, 50 mm edge distance. Grout pad 25 mm.

Step 2 — Concrete Bearing: For 400 mm base on 800 mm foundation: bearing strength = 0.85 times 0.65 times 30 times sqrt(640,000/160,000) = 33.15 MPa. Applied stress = 1800,000 / 160,000 = 11.25 MPa. OK.

Step 3 — Bolt Tension: T_max = 80/0.30 - 1800/4 = -183.3 kN (net compression). No tension in bolts.

Step 4 — Shear: V per bolt = 65/4 = 16.3 kN. V_r (M24 threaded) = 50.0 kN. OK (33% utilisation).

Selected: 400x400x25 mm 300W base plate, 4-M24 F1554-55 anchors, 300 mm embedment.

Worked Example 2 — Shear-Dominated Canopy Column (Vancouver)

Problem: HSS 152x152x9.5 canopy column (350W): N_f = 95 kN tension (wind uplift), V_f = 120 kN shear, M_f = 45 kN.m. 600x600 mm C35 pier. 4-M30 F1554-55 anchors at 250 mm gauge.

Step 1 — Bolt Tension: T per bolt = (95/4 + 45/0.50)/2 = 56.9 kN. T_r (M30, A_n = 561 mm^2) = 0.75 times 0.80 times 561 times 517 / 1000 = 174.3 kN. OK (33%).

Step 2 — Bolt Shear: V per bolt = 120/4 = 30.0 kN. V_r (M30 threaded) = 79.4 kN. OK.

Step 3 — Combined Interaction: (56.9/174.3)^2 + (30.0/79.4)^2 = 0.107 + 0.143 = 0.250. OK.

Step 4 — Concrete Breakout: With h_ef = 350 mm and c_a1 = 125 mm (edge < 1.5h_ef), breakout governs. Increase pier to 750x750 mm to eliminate edge effects. With h_ef = 400 mm: N_Rd,c,group = 325 kN > 227.6 kN demand. OK.

Final selection: 4-M30 F1554-55 anchors at 400 mm embedment, 750x750 mm C35 pier, 500x500x30 mm base plate 300W.

Edge Distance and Spacing Requirements

Per CSA A23.3 Annex D:

FAQ

What anchor bolt grade for Canadian commercial buildings? ASTM F1554 Grade 55 is standard. Grade 36 for secondary elements. Grade 105 for heavy moment frames.

When does concrete breakout govern over bolt tension? Breakout governs when embedment depth is shallow. For M24 F1554-55 anchors in C30 concrete, breakout exceeds bolt tension at h_ef > 220 mm.

How does CSA A23.3 Annex D differ from ACI 318 Chapter 17? Harmonised equations with metric units and Canadian material standards. Numerically identical results when unit conversions are consistent.

What grout thickness under Canadian base plates? Minimum 25 mm non-shrink grout per CSA S16 and CSA A23.1. 40-50 mm for heavy columns (>2000 kN).

Are J-bolts or L-bolts permitted for structural applications? No — CSA A23.3 Annex D covers headed anchors and post-installed anchors only. J-bolts and L-bolts require testing or rational analysis.

Why do CSA load combinations sometimes produce tension in nominally compression columns? Wind uplift (0.9D + 1.4W per NBCC) can produce net tension at column bases for portal frames, canopy columns, and building corners. Always check the full load combination envelope.

Corrosion Protection for Canadian Anchor Bolts

Canadian climate conditions demand careful attention to anchor bolt corrosion protection. Exposed anchor bolts at column bases are vulnerable to de-icing salts in parking garages and bridge abutments (chloride-induced corrosion), condensation at the cold joint between steel base plate and concrete foundation, and freeze-thaw cycling accelerating coating degradation in exposed conditions.

Protection Methods

For standard Canadian commercial buildings (interior columns, conditioned space), F1554-55 bolts with a zinc-rich primer are typically sufficient. For exterior canopies, parking structures, and bridges, specify hot-dip galvanised F1554-55 or upgrade to F1554-105 with HDG and a duplex coating system per CSA S16 Clause 28.

Anchor Bolt Projection Above Grout

Canadian practice specifies a minimum 75 mm projection of the anchor bolt above the grout pad to allow for base plate thickness, levelling nuts, washers, and full nut engagement. For 30-40 mm base plates, specify 150 mm minimum projection. The threaded portion must extend fully through the base plate plus two nuts (levelling nut below, holding-down nut above) plus three full threads of projection per CSA S16 standard practice.

Anchor Bolt Installation Tolerances

Per CSA W59 (Welded Steel Construction) and CSA S16 Clause 29:

• Bolt group location: +/- 3 mm from theoretical position in plan
• Individual bolt location: +/- 1.5 mm from group position
• Plumb (verticality): 1:100 maximum from vertical (1 mm per 100 mm projection)
• Bolt projection above concrete: +/- 5 mm from specified
• Grout pad thickness: minimum 25 mm, maximum 50 mm without supplemental reinforcement

Oversized base plate holes (3-6 mm larger than bolt diameter) accommodate normal installation tolerances. For bolts out of tolerance beyond the 3 mm group allowance, field-drilled base plates or slotted holes with plate washers may be required. Always coordinate with the structural engineer before field modifications.

Additional FAQ

What about anchor bolts in seismic zones?

CSA S16 Clause 27 requires anchor bolts in seismic force-resisting systems to develop their full tension capacity with ductile behaviour. This typically requires the anchor bolt to yield before the concrete breakout failure occurs — a "capacity-protected" design. For high-seismic zones (Vancouver, Montreal), use F1554-55 bolts (which have better elongation than Grade 105), deeper embedment to ensure breakout exceeds bolt tension, and additional confining reinforcement around the anchor group per CSA A23.3 Annex D.

How do I handle anchor bolts in a slab-on-grade without a pier?

When columns are founded on a slab-on-grade without a thickened pier, the concrete breakout capacity is severely limited by the slab thickness. For a 150 mm SOG, h_ef max = 120 mm (allowing for cover). This produces very low breakout capacity — typically only 15-25 kN per anchor. For any structural column, a thickened footing or pier is required. Slab-on-grade anchors are suitable only for non-structural elements (handrails, small canopy posts, partition bracing).

Related Pages

• CSA S16 Base Plate Design — Canadian Guide
• CSA S16 Column Design — Worked Example
• CSA S16 Bolt Capacity — Bolt Tables
• CSA S16 Bolt Hole Sizes — Clearances
• CSA S16 Load Combinations — NBCC ULS
• Canadian Steel Grades — G40.21 350W
• CSA Stub Column — S16 Compression Capacity
• CSA Beam Sizes — G40.21 Hot-Rolled Sections
• Canadian Compact Section Limits — CSA S16 Table 2
• Base Plate & Anchor Calculator — Free Tool

Educational reference only. Verify anchor bolt design against CSA S16:24, CSA A23.3-19, and ASTM F1554. Cold-region notch toughness requirements may apply per CSA S16 Clause 27. Results are PRELIMINARY — NOT FOR CONSTRUCTION without independent P.Eng. verification.