Cast-In Anchor Tension Concrete Breakout (ACI 318-19 Ch. 17)

Concrete breakout capacity of a headed anchor in tension by the ACI 318-19 CCD method.

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Checked against published worked examples from: ACI 318-19 Section 17.6.2 (concrete breakout in tension, CCD method).

Details, formula, and sources

ScopeNb = kc lambda sqrt(f'c) hef^1.5 (kc 24 cast-in / 17 post-installed), edge-modified to Ncb and design phiNcb. The hef^1.5 cone and near-edge knockdown that anchor-embedment never checks; a near edge can cut capacity 25% before the steel yields.

Formula or tableNb = kc lambda sqrt(f'c) hef^1.5 (kc 24 cast-in, 17 post-installed); ANco = 9 hef^2; psi_ed = 0.7 + 0.3 ca1/(1.5 hef) when ca1 < 1.5 hef; for a concentric group of n1 x n2 anchors ANc = [min(ca1, 1.5 hef) + (n1 - 1) min(s1, 3 hef) + 1.5 hef] x [3 hef + (n2 - 1) min(s2, 3 hef)] <= n ANco (17.6.2.1); Ncb(g) = (ANc/ANco) psi_ed psi_c,N psi_cp,N Nb (psi_c,N 1.0 cracked, 1.25 cast-in / 1.4 post-installed uncracked; psi_cp,N = max(ca1, 1.5 hef)/(4 hef) for an uncracked post-installed anchor with ca1 < 4 hef, else 1.0); phiNcb = phi Ncb, phi 0.70 cast-in and 0.65 / 0.55 / 0.45 post-installed Category 1 / 2 / 3 (Condition B, no supplementary reinforcement).

Source and editionThe ACI 318-19 Section 17.6.2 concrete breakout strength in tension (CCD method), by name.

Free accessACI 318 is readable free through the ACI online reading room at concrete.org; the Chapter 17 anchoring provisions are in the published code.

What governsEstimate. AHJ and licensed professional govern.

API field namesembedment_in, fc_psi, edge_distance_in, anchor_type, lambda, nb_lb, phi_ncb_lb

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