Circular Column — ACI 318-25 Design

1 · Input data

Design check of a circular reinforced concrete column (a continuous spiral or circular ties) with the longitudinal bars on one circle, under factored axial compression and moment about one principal axis, to ACI CODE-318-25 (procedure ENG-2026-10-029): the transverse type and its two strength consequences; the geometry A_g, A_ch and the bar circle; the longitudinal reinforcement limits; the slenderness test and, where it is needed, the moment magnification of 6.6.4; the axial cap of Table 22.4.2.1; the strength reduction factor φ from Table 21.2.2 with the new 21.2.2.3 cap; the P–M interaction diagram built by strain compatibility over the circular compression segment (the circle is never replaced by an equivalent rectangle); the design check of 10.5.1.1; the spiral ratio of Eq. (25.7.3.3) or the tie rules of 25.7.2; and the bar spacing, cover and compression lap splices. Every parameter below is required. Press Solve the column check when the card is complete — if anything is missing or malformed the page opens a pop-up naming each parameter and computes nothing; an input that is well-formed but outside the procedure is refused with the clause that refuses it.

Section and materials

D — outside diameter of the circular column (in)

f′_c — specified compressive strength of concrete (psi)

f_y — longitudinal reinforcement yield strength (psi, 80,000 max)

f_yt — spiral or tie yield strength (psi, 100,000 max in the spiral ratio)

Concrete exposure (Table 20.5.1.3.1, columns row)

Transverse reinforcement

Transverse reinforcement type (25.7.3 spiral / 25.7.2 ties)

Spiral or tie bar size (25.7.3.2 / 25.7.2.2)

Spiral pitch or tie spacing, on center (in)

Longitudinal reinforcement A_st

Longitudinal bar size

Number of longitudinal bars on the circle (3 or more)

Factored forces

P_u — factored axial compression (kip)

M_u — factored moment about the bending axis (kip-ft)

Slenderness and framing

ℓ_u — unsupported length (ft)

k — effective length factor (1.0 nonsway)

Framing condition (6.2.5.1)

M₁/M₂ — end moment ratio (negative single curvature, positive double)

Transverse load between supports? (6.6.4.5.3)

β_dns — sustained axial load ratio (0.6 typical)

Concrete and aggregate

d_agg — nominal maximum aggregate size (in)

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2 · Solution

No solution yet — complete every input in the card above and press Solve the column check. This card stays empty until a solution is computed, and it is emptied again the moment any input changes, so a displayed solution always belongs to the inputs on screen.