Structural Anchorage in Ontario: CSA A23.3 Annex D, Post-Installed Anchors & Special Inspections

CSA A23.3 Annex D: Ontario's Anchor Design Standard

CSA A23.3-19 (Design of Concrete Structures) Annex D governs the design of anchorages in concrete structures throughout Ontario. Annex D is incorporated by reference into OBC Division B Part 4 through NBCC 2020's reference to CSA A23.3, making it the mandatory standard for any structural anchor in an OBC-regulated building.

Annex D covers two anchor categories:

• Cast-in-place anchors: Headed bolts, headed studs, and hooked bolts embedded in concrete during the pour. These anchor types generally achieve higher capacity than post-installed anchors of the same diameter because the head creates a mechanical bearing failure mode (pullout) rather than relying solely on friction or adhesion.
• Post-installed anchors: Anchors installed into hardened concrete by drilling a hole and inserting an expansion, undercut, or adhesive anchor. Post-installed anchors are evaluated under ICC-ES or CCWU evaluation reports confirming their performance under Annex D provisions.

Six Anchor Failure Modes

CSA A23.3 Annex D defines six failure modes that must be evaluated in anchor design:

1. Steel fracture: The anchor bolt or rod fails in tension or shear. Governed by the steel cross-section and material grade (typically CSA G40.21 300W or ASTM F1554 equivalent). The most ductile failure mode — preferred over concrete failure in seismic design.
2. Concrete breakout (tension): A cone of concrete pulls out around the anchor. The breakout capacity is proportional to the anchor effective embedment depth to the 1.5 power — doubling the embedment depth increases breakout capacity by approximately 2.8×. Reduced significantly by proximity to edges or other anchors.
3. Concrete breakout (shear): A shear pryout failure at the concrete edge. Governs for anchors in thin edge conditions, where the distance from the anchor to a free edge is small relative to the embedment depth.
4. Anchor pullout: The anchor body pulls through the concrete without a full concrete cone — governs for anchors with small heads (J-bolts, small diameter cast-in rods). Expansion and adhesive anchors have specific pullout failure mode evaluations from their ICC-ES or CCWU evaluation reports.
5. Side-face blowout: For large-diameter headed anchors near a concrete edge, the concrete fails in splitting along the side of the anchor rather than as a full cone. Governed by edge distance relative to head bearing area.
6. Pryout failure: Shear failure behind a short, stiff anchor. Pryout governs when anchors have small edge distances and low embedment depth relative to diameter — controls for some adhesive and expansion anchor applications under shear.

Types of Post-Installed Anchors

• Torque-controlled expansion anchors (wedge anchors): When tightened, the wedge or sleeve expands against the drill hole wall. Quick installation. Sensitive to drill hole diameter tolerance and concrete quality. Not suitable for cracked concrete without a cracked-concrete evaluation. Common for light-to-medium load applications.
• Undercut anchors: A special drill bit creates an undercut in the bottom of the hole; the anchor locks into the undercut mechanically. Highest-performing mechanical anchor for heavy loads. Suitable for cracked concrete. Used in facade support, transfer beam connections, and other high-load applications.
• Adhesive anchors (chemical anchors): Two-component resin injected into a cleaned hole bonds a threaded rod or rebar insert to the concrete. High pullout capacity in both cracked and uncracked concrete. Required for rebar dowel extensions. Cure time is temperature-sensitive — installation in cold Ontario weather requires extended cure before loading and may require heating of the adhesive. Overhead installation requires special low-sag adhesive and alignment tools.
• Cast-in headed bolts and anchors: The best-performing anchor type — installed before the concrete pour. Standard in new construction for mechanical equipment bases, column base plates, precast connections, and curtain wall support brackets. Not available for retrofit applications requiring post-installed anchors.

When P.Eng Design Is Required

A P.Eng is required for anchor design in Ontario in the following situations:

• Anchors attaching structural elements that carry gravity or lateral loads (all OBC Part 4 buildings)
• Fall protection anchors and horizontal lifeline connections (OHSA)
• Facade, cladding, and curtain wall structural support anchors
• Heavy mechanical equipment (cooling towers, generators, HVAC units) attachments to structural slabs or roofs
• Seismic bracing attachments under NBCC 2020
• Any anchor where failure would create a life safety hazard or significant structural consequence

For OBC Part 9 residential work, P.Eng anchor design is less commonly required for low-consequence applications (deck ledger bolts, handrail post anchors) — but where a ledger bolt failure could cause a deck collapse, Ontario building departments increasingly expect engineering documentation.

Installation Verification for Anchors

For critical post-installed anchors in concrete, owners and engineers often require independent installation verification by a qualified testing agency or inspector. That review typically confirms:

• Anchor product matches the P.Eng design specification (correct diameter, embedment depth, material)
• Hole diameter, depth, and cleanliness comply with the manufacturer's installation instructions and P.Eng design
• For expansion anchors: installation torque meets the specified minimum value (torque test per anchor)
• For adhesive anchors: adhesive type and batch, hole cleaning method (brushing, blowing, vacuuming), adhesive mixing and injection procedure, orientation (horizontal, overhead), and cure time before loading
• Minimum edge distances and anchor spacing comply with the P.Eng design

Pull-Out Testing in Ontario

Proof-load pull-out testing is required or recommended in Ontario for:

• High-consequence applications where failure would have significant safety or structural consequences
• Installations in substrates with uncertain concrete quality (older buildings with unknown concrete strength or condition)
• Post-installed adhesive anchors in unusual orientations or substrates
• Where quality assurance testing is required by the P.Eng design or specified as a condition of the building permit

Pull-out testing is typically performed by a testing laboratory using a calibrated hydraulic hollow-core jack. The test protocol follows ASTM E488 or the manufacturer's specified proof-load test procedure. A test load equal to 1.5× the design load is typically applied for 10 minutes. Anchors that hold the proof load without visible distress or excessive displacement pass. A representative sample — often 5–10% of installed anchors, or a minimum number specified by the engineer — is tested.

Seismic Anchor Design in Ontario

NBCC 2020 seismic requirements apply to structural elements in buildings and to non-structural components (mechanical, electrical, plumbing equipment) in OBC Part 4 buildings. Seismic anchor design requires:

• Seismic design categories and importance factors per NBCC 2020 Chapter 4
• Ductile anchor design — CSA A23.3 Annex D seismic provisions require that in Seismic Design Category C and above, anchors be designed to yield in the steel (ductile failure mode) rather than fail in concrete breakout (brittle). This significantly affects anchor sizing in Ottawa and eastern Ontario where seismic demands are higher.
• NBCC Part 4 Sentence 4.1.8.19 governing non-structural components — mechanical equipment anchors in Part 4 buildings must be designed for the seismic equipment force Vp based on component importance, acceleration, and weight