ACI 318-19 Chapter 17: All Anchor Limit States Explained for Seismic Design

Every anchor failure in a real earthquake corresponds to one of the seven limit states in ACI 318-19 Chapter 17. Designing an anchor means sizing it so the lowest-capacity limit state has more capacity than the seismic demand. This article gives you the limit states in the order plan reviewers expect to see them, with the equation each one comes from and the reduction factors that catch engineers off-guard.

Limit state 1 — Steel strength in tension (N_sa)

ACI 318-19 §17.6.1: φN_sa = φ · n · A_se,N · f_uta, with φ = 0.75 for ductile steel anchors. f_uta is capped at the lesser of 1.9 f_ya and 125,000 psi. Use the manufacturer's published net tensile area (A_se,N) and ultimate strength from the ESR.

Limit state 2 — Concrete breakout in tension (N_cbg)

§17.6.2: N_cbg = (A_Nc/A_Nco) · Ψ_ec,N · Ψ_ed,N · Ψ_c,N · Ψ_cp,N · N_b. The basic capacity N_b is a function of f'_c and effective embedment h_ef with the k_c coefficient (17 for cast-in or 24 for post-installed, when permitted in cracked vs uncracked — see cracked vs uncracked concrete).

Limit state 3 — Pullout (N_pn)

§17.6.3: N_pn = Ψ_c,P · N_p. For post-installed expansion / undercut / screw / adhesive anchors, take N_p directly from the ESR. For cast-in headed bolts, N_p = 8 · A_brg · f'_c. φ = 0.70 for cracked concrete.

Limit state 4 — Side-face blowout (N_sb)

§17.6.4: applies when c_a1 < 0.4 h_ef for headed anchors deep in concrete. Catches engineers who set headed bolts too close to a free edge in a thick footing.

Limit state 5 — Steel strength in shear (V_sa)

§17.7.1: φV_sa = φ · n · 0.6 · A_se,V · f_uta for cast-in-place; the 0.6 is replaced with the manufacturer's value from the ESR for post-installed. φ = 0.65 for ductile shear.

Limit state 6 — Concrete breakout in shear (V_cbg)

§17.7.2: a function of edge distance c_a1, embedded anchor diameter, and concrete strength. The Ψ_ed,V and Ψ_c,V reductions can be brutal — at c_a1 = 1.5 d_a, the breakout capacity is a fraction of the steel capacity. See edge distance and spacing.

Limit state 7 — Pryout (V_cpg)

§17.7.3: V_cpg = k_cp · N_cbg, with k_cp = 1.0 for h_ef < 2.5 in. and 2.0 otherwise. Pryout often controls shallow anchors.

The §17.8 interaction — every pair must check

Per §17.8.3: N_ua/φN_n + V_ua/φV_n ≤ 1.2 for each pair (steel/steel, breakout/breakout, etc.). See our tension vs shear article.

Seismic amplifications — §17.10 (cross-referenced from ASCE 7-22 §13.4.2)

• Ω_0p on concrete-controlled limit states unless an exception applies.
• 0.75 reduction on φN_cbg, φV_cbg, φN_pn, φN_sb per §17.10.6 (the seismic concrete capacity reduction).
• Adhesive anchors: must be qualified per ACI 355.4 with seismic certification per §17.10.5 (c).
• Anchor reinforcement per §17.5.2.1 can shift the limit state from concrete to steel.

Order of operations on a real calc

1. Compute demand T and V per anchor (and the orthogonal direction).
2. Compute every limit state capacity from the ESR or first principles.
3. Apply Ω_0p to concrete-controlled demands.
4. Apply the 0.75 §17.10.6 factor to concrete capacities in seismic.
5. Compute DCR for each pair via §17.8.
6. Identify the governing limit state and report the DCR.

What the cover sheet should look like

• Anchor designation, embedment, edge distance, spacing.
• Concrete f'_c, density, cracked/uncracked.
• Each limit state φ-capacity tabulated.
• Ω_0p, the §17.10.5 exception (if any), and the 0.75 §17.10.6 factor.
• The §17.8 interaction DCR table with the governing row highlighted.

How PANACHE ENGINEERING handles this

Our Seismic Anchor Calculator evaluates every limit state in §17.6, §17.7, §17.8, and §17.10 on every run, and outputs a stamped DCR table with the governing row called out. Need a full PE/SE-stamped package? Send us your data.