Home / Tools / ACI 318-19 SMF Joint C · Concrete · Seismic

ACI 318-19 Special Moment Frame Beam-Column Joint (§18.8)

Joint shear demand from beam probable moments (1.25f_y) and column shear, and joint shear strength from the eight-row Table 18.8.4.3 of ACI 318-19 (column and beam continuity, transverse-beam confinement), with the joint-depth requirements of 18.8.2.3.

Joint

Joint type

Column above

Beam in direction of V_u

Transverse beams (15.2.8)

Column h (∥ beam) in.

Column width in.

ℓ_c (inflection to inflection) in.

x (beam axis to column side) in.

Beams and materials

b_w in.

Beam depth in.

d in.

Largest bar d_b in.

A_s top in.²

A_s bottom in.²

f′c psi

Bar grade

Concrete

Results

M_pr⁻ · M_pr⁺—

T + C − V_col = V_u—

γ (Table 18.8.4.3) · φ · A_j—

V_u / φV_n—

Joint depth h vs required (18.8.2.3)—

ACI 318-1918.8.2.1 (1.25f_y), 18.8.2.3 and 18.8.2.3.1 (joint depth, Grade 80), 18.8.4.1–18.8.4.3 and Table 18.8.4.3 (V_u, φ, V_n), 21.2.4.4 (φ = 0.85), 15.2.6–15.2.8 (continuity, confinement), 15.4.2.4 (A_j). Clause numbers only.

VerifiedTable 18.8.4.3 rows, φ and 18.8.2.3 from Ghosh & Taylor (Concrete International, 2021); M_pr and joint equilibrium from STRUCTURE (2018). Version traps: Table 18.8.4.1 (318-14) had three rows and no discontinuous-column cases; φ for SMF joints is 21.2.4.4 (21.2.4.3 in 318-14); intermediate-frame joints use φ = 0.75.

Preliminary calculation tool. Final design requires the full text of ACI 318 and review by a licensed PE. This tool follows ACI 318-19, the edition referenced by the 2021 and 2024 IBC; ACI CODE-318-25 was published in January 2025 and is expected in the 2027 IBC (changes include development length equations and seismic provisions).