---------------------- | ----------------------------- | ----------- | -------------- | ---------- | | Concrete breakout tension | 17.4.2 (CCD method) | Cl 14.4.2.2 | Cl 7.2.1.4 | Cl D.6.2.2 | | Concrete breakout shear | 17.5.2 | Cl 14.4.3.2 | Cl 7.2.2.4 | Cl D.6.3.2 | | Pullout strength | 17.4.3 | Cl 14.4.2.3 | Cl 7.2.1.5 | Cl D.6.2.3 | | Side-face blowout | 17.4.4 | Cl 14.4.2.4 | Cl 7.2.1.6 | Cl D.6.2.4 | | Steel strength tension | 17.4.1 | Cl 14.4.2.1 | Cl 7.2.1.2 | Cl D.6.2.1 | | Concrete pryout (shear) | 17.5.3 | Cl 14.4.3.3 | Cl 7.2.2.5 | Cl D.6.3.3 | | Combined tension+shear | 17.6 | Cl 14.4.4 | Cl 7.2.3 | Cl D.7 | | phi factors (tension) | 0.75 (steel), 0.65 (concrete) | 0.80 | 1.5 (gamma_Mc) | 0.85 |

Key difference: EN 1992-4 uses partial safety factors (gamma_Mc = 1.5 for concrete, gamma_Ms = 1.2 for steel), while AISC 360 applies phi factors (0.75 for ductile steel, 0.65 for concrete breakout). AS 4100 uses capacity factor phi = 0.80 for all anchor failure modes.

Step-by-Step Example

Problem: Determine the tension capacity of a 3/4-inch diameter cast-in-place headed anchor bolt (F1554 Grade 36) embedded 6 inches in 3,000 psi normal-weight concrete. Edge distance = 6 inches in both directions (corner condition). No adjacent anchors.

Step 1 — Steel strength (AISC 360-22 Eq 17.4.1.2): Nsa = Ase _ futa = 0.334 _ 58,000 = 19,372 lb = 19.4 kips phi*Nsa = 0.75 * 19.4 = 14.5 kips

Step 2 — Concrete breakout strength (AISC 360-22 Eq 17.4.2.1b): ANc = (c1 + 1.5hef) * (c2 + 1.5hef) = (6 + 9) * (6 + 9) = 225 in^2 ANco = 9 _ hef^2 = 9 _ 36 = 324 in^2 ANc/ANco = 225/324 = 0.694

psi = sqrt(6) / 1.5 = 1.63 (edge effect for corner, ca1 = 6 in)

Nb = kc _ lambda_a _ sqrt(f'c) _ hef^1.5 = 24 _ 1.0 _ sqrt(3000) _ 6^1.5 Nb = 24 _ 54.77 _ 14.70 = 19,310 lb = 19.3 kips

Ncbg = (ANc/ANco) _ psi _ Nb = 0.694 _ 1.63 _ 19.3 = 21.8 kips phi*Ncbg = 0.65 * 21.8 = 14.2 kips

Step 3 — Pullout strength (AISC 360-22 Eq 17.4.3.1): Npn = 8 _ Abrg _ f'c = 8 _ 0.442 _ 3000 = 10,608 lb = 10.6 kips phi*Npn = 0.70 * 10.6 = 7.4 kips

Step 4 — Governing tension capacity: Governing = min(14.5, 14.2, 7.4) = 7.4 kips (pullout governs)

Result: Design tension capacity = 7.4 kips. Pullout governs — consider increasing embedment depth or using a larger head to increase bearing area.

Frequently Asked Questions

What is the minimum embedment depth for anchor bolts in steel construction? For cast-in-place headed anchor bolts, the minimum effective embedment (hef) is typically 4 bolt diameters (4db) or 2 inches, whichever is greater. In seismic applications (AISC 341), a minimum of 12db may be required to ensure ductile behavior. For post-installed anchors, follow the manufacturer's published ICC-ES ESR report for minimum embedment.

How does edge distance affect anchor embedment capacity? Edge distance is one of the most influential parameters. At edge distances less than 1.5 * hef, the concrete breakout cone is truncated by the free edge, reducing capacity below the full breakout strength. At very small edge distances (under 3-4 inches), side-face blowout may govern for deep embedments. Increasing edge distance by even 1 inch can significantly improve capacity — typically by 10-20% for anchors near the edge.

What is the difference between concrete breakout and pullout failure? Concrete breakout is a cone-shaped failure propagating from the embedded head to the concrete surface at roughly a 35-degree angle. It depends on embedment depth and edge distance. Pullout is the anchor pulling the head through the concrete without surface breakout — it is governed by the bearing area of the head and concrete compressive strength. Pullout typically governs for shallow embedments or small headed areas, while breakout governs for deeper embedments.

Which design standard covers anchor bolt embedment? AISC 360-22 Chapter 17 (formerly Appendix D) covers anchor design in the US. EN 1992-4 governs in Europe. AS 4100 Section 14 covers in Australia, and CSA A23.3 Annex D covers in Canada. All four standards use the concrete capacity design (CCD) method with a 35-degree breakout cone, but differ in resistance factors and edge effect equations.

Is this anchor embedment calculator free to use? Yes, completely free with unlimited calculations. No registration or account required. Use it for preliminary anchor sizing, embedment depth checks, and design verification across AISC 360, AS 4100, EN 1992-4, and CSA A23.3.

Concrete Breakout Failure Modes

ACI 318-19 Chapter 17 establishes seven distinct concrete failure modes for anchors in tension and shear. Understanding which mode governs is essential for safe anchor embedment design, as the design strength is controlled by the weakest failure path.

Tension Failure Modes (ACI 318-19 Section 17.6)

1. Concrete breakout in tension (17.6.2): A conical failure surface propagates from the embedded anchor head to the concrete surface at approximately 35 degrees from the vertical axis. The breakout capacity depends on the projected area of the cone (ANc), the basic concrete breakout strength (Nb), and modification factors for edge distance, eccentricity, and cracking. For a single anchor away from edges, ANco = 9 x hef^2. When edges truncate the cone, ANc is reduced accordingly and the capacity drops proportionally.

2. Pullout strength (17.6.3): The anchor pulls through the concrete without a surface cone, governed by the bearing area of the anchor head against the concrete. The pullout capacity Npn = 8 x Abrg x f'c for cast-in-place headed studs. Pullout often governs for shallow embedments with small head bearing areas. Increasing the head size (from standard to heavy hex or a plate washer) can significantly improve pullout capacity without increasing embedment depth.

3. Side-face blowout (17.6.4): When an anchor is near a free edge (ca1 < 0.4 x hef), the concrete can blow out laterally from the side face before a full surface cone develops. This mode is considered separately from breakout and can govern for deep embedments with small edge distances. For headed anchors with multiple edges near the anchor (ca2 < 3ca1), an additional reduction factor applies per ACI 17.6.4.2.

4. Steel strength in tension (17.6.1): The anchor bolt itself yields or fractures in tension. The steel strength Nsa = Ase x futa, where Ase is the effective tensile stress area (accounting for the reduced area at threads). For F1554 Grade 36 anchors, futa = 58 ksi. The phi factor is 0.75 for ductile steel elements.

Shear Failure Modes (ACI 318-19 Section 17.7)

5. Concrete breakout in shear (17.7.2): A half-cone breakout surface forms in the direction of shear loading. The capacity depends on the anchor diameter, edge distance in the direction of shear (ca1), and the concrete compressive strength. The reference capacity Vb is proportional to (le/da)^0.2 x sqrt(da) x sqrt(f'c) x ca1^1.5.

6. Concrete pryout in shear (17.7.3): For short, stiff anchors loaded in shear away from free edges, the anchor can pry out a concrete plug by rotating. The pryout capacity Vcp = kcp x Ncp, where Ncp is the concrete breakout capacity in tension and kcp = 1.0 for hef < 2.5 in or 2.0 for hef >= 2.5 in.

7. Steel strength in shear (17.7.1): The anchor bolt shears off. For cast-in-place headed studs, the steel shear strength Vsa = 0.6 x Ase x futa (for headed studs where the shear plane passes through the threaded portion). The phi factor is 0.65 for non-ductile shear.

Key ACI 318-19 Design Parameters

Parameter Symbol Typical Range Notes
Effective embedment hef 4db to 25db Measured from concrete surface to bearing surface of head
Edge distance (shear dir.) ca1 1.5hef (full cap.) to 4db (min) Most influential shear parameter
Concrete strength f'c 2,500 to 8,000 psi Breakout proportional to sqrt(f'c)
Anchor diameter da 1/2" to 2" typical Steel strength proportional to da^2
Cracked vs. uncracked - kc = 17 (cracked), 24 (uncracked) Uncracked assumption requires analysis showing concrete remains in compression under service loads

Practical Edge Distance and Spacing Rules

Condition Minimum per ACI 17 Recommended for Full Capacity
Edge distance (any direction) No absolute minimum; check blowout if ca < 0.4hef >= 1.5 x hef
Anchor spacing 4 x da >= 3 x hef (to avoid cone overlap)
Embedment depth 4 x da (absolute min for headed studs) 8-12 x da (typical for structural columns)
Concrete member thickness >= hef + 2 x da (or h_min per ESR report) >= 1.5 x hef

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This page is provided for general technical information and educational use only. It does not constitute professional engineering advice. All structural designs must be verified by a licensed Professional Engineer (PE) or Structural Engineer (SE). The site operator disclaims liability for any loss or damage arising from the use of this page.