Concrete Anchor Pryout in Shear (ACI 318-19 17.7.3)
The shear mode that governs SHORT stiff anchors AWAY from an edge - exactly where the edge-breakout check exits.
Example
You enter
- Effective embedment hef (in) 6
- Concrete strength f'c (psi) 4000
- Nearest edge distance ca1 (in, large = away) 100
- Anchor type cast-in
- Lightweight factor lambda_a (1.0 normal weight) 1
You get
- Tension breakout Ncb (the base) 22308 lb (22.3 kip)
- Pryout coefficient kcp 2.0 (hef >= 2.5 in)
- Nominal pryout Vcp 44617 lb (44.6 kip)
- Design pryout phiVcp 31232 lb (31.2 kip)
Details, formula, and sources
The anchor pries a breakout body out of the surface behind it, so Vcp = kcp x Ncb rides on the tension-breakout strength, with kcp jumping 1.0 -> 2.0 at hef = 2.5 in; phiVcp = 0.70 Vcp. A 6-in cast-in anchor away from edges checks 31.2 kip design pryout. A shear design takes the LEAST of steel, edge breakout, and pryout.
Vcp = kcp x Ncp with Ncp = Ncb (the 17.6.2 tension-breakout strength); kcp = 1.0 for hef < 2.5 in, 2.0 for hef >= 2.5 in; phiVcp = 0.70 Vcp (Condition B).
The ACI 318-19 Section 17.7.3 concrete pryout strength of an anchor in shear (17.7.3.1a), by name.
ACI 318 is readable free through the ACI online reading room at concrete.org; the Chapter 17 anchoring provisions are in the published code.
Estimate. AHJ and licensed professional govern.
Field names used by the API: embedment_in, fc_psi, edge_distance_in, anchor_type, lambda, ncb_lb, kcp, vcp_lb, phi_vcp_lb
- Pryout base Ncp = Ncb, the tension concrete-breakout strength; the tile calls the landed breakout routine so the two can never driftACI 318-19 17.7.3.1
- kcp threshold 1.0 below hef = 2.5 in, 2.0 at or above itACI 318-19 17.7.3.1
- Scope single anchor away from an edge; steel shear and the 17.7.2 edge breakout are separate checksACI 318-19 17.7.1, 17.7.2