16x16 Column, Min-Eccentricity Advisory
Minimum-eccentricity advisory for a 16x16 / 8-#9 tied column per ACI 318-19: M2,min evaluation when the applied moment is small or zero.
Checked about X: depth h = 16 in
Both axial and moment D/C ratios ≤ 1.00.
Advisory: user-entered M₂ = 0.500 kip-ft is below M₂,min = Pᵤ·(0.6 + 0.03·h) = 27.000 kip-ft. ACI 318-19 §6.6.4.5.4 formally scopes this bound to slender-column moment magnification; it is not code-required for calcnote's short-column scope. Calculation proceeds using user-entered M₂. Confirm construction-tolerance eccentricity and unmodeled lateral effects are captured elsewhere in the load path.
Full rationale: methodology on ACI 318-19 §6.6.4.5.4
P-M interaction diagram
Demand (Pu, Mu) tested against the φ-reduced capacity envelope. Operating point (φPn, φMn) shown on the boundary. φ is computed per anchor from εt (§21.2.2); your operating point lies in the compression-controlled region; how the φ transition works.
Interaction Diagram Points (8 anchors, ACI 318-19 Table 22.4.2.1)
| Anchor | Description | c (in) | εt | φ | φPn (kip) | φMn (kip-ft) |
|---|---|---|---|---|---|---|
| 1 | Pure compression cap | N/A | N/A | 0.65 | 797.68 | 0.00 |
| 2 | Cap intersection | 17.35 | -0.00067 | 0.65 | 797.64 | 102.66 |
| 3 | Compression-controlled limit (εt = εty) | 7.99 | 0.00207 | 0.65 | 270.89 | 250.77 |
| 4 | Transition lower (εt = εty + 0.0015) | 6.17 | 0.00357 | 0.78 | 221.10 | 272.57 |
| 5 | Tension-controlled limit (εt = εty + 0.003) | 5.02 | 0.00507 | 0.90 | 171.64 | 286.75 |
| 6 | Tension-controlled deep (εt = εty + 0.008) | 3.10 | 0.01007 | 0.90 | -3.74 | 212.22 |
| 7 | Pure bending | 3.25 | 0.00946 | 0.90 | 0.00 | 213.93 |
| 8 | pure_tension | N/A | N/A | 0.90 | -432.00 | 0.00 |
| Quantity | Value |
|---|---|
| Pu (factored axial demand, kip) | 300.00 |
| φPn (axial capacity at operating point, kip) | 797.68 |
| Mu (= M2, design moment, kip-ft) | 0.50 |
No transverse load between supports. Cm from end-moment ratio per ACI 318-19 §6.6.4.5.3(a). |
|
| φMn (moment capacity, kip-ft) | 1.33 |
| c (neutral axis depth, in) | N/A |
| εt (extreme tension strain) | N/A |
| φ (strength reduction factor) | 0.65 |
| φ regime (§21.2.2) | Compression-controlled φ = 0.65 throughout (εt ≤ εty = 0.00207) |
| D/C axial | 0.37 |
| D/C moment | 0.37 |
| kl/r about X | 25.00 |
Nonsway frames only (ACI 318-19 §6.6.4.3). The other axis (about Y) was not checked. kl/r about Y = 25.00, which exceeds the worst-case short-column limit of 22 (actual limit depends on the other-axis moments). Run the check about Y separately. Run about Y |
|
| kl/r limit | 34.00 |
| Tie spacing limit (§25.7.2.1) | 16.00 in (governed by b) |
| Bar clear spacing (§25.2.3) | 2.54 in ≥ 1.69 in |
Force Decomposition at Operating Point (cap-governed; breakdown at Pn,max)
| Component | Force (kip) | Moment (kip-in) |
|---|---|---|
| Cc (concrete compression) | 1,088.00 | 0.00 |
| Cs (steel in compression) | 446.00 | 0.00 |
| Ts (steel in tension) | 0.00 | 0.00 |
| Total = Pn, Mn | 1,534.00 | 0.00 |
| Layer | Bars | d (in) | εs | fs (ksi) | Force (kip) | Lever (in) | Moment (kip-in) |
|---|---|---|---|---|---|---|---|
| 1 | 4 | 2.50 | 0.00295 | 60.00 | 223.00 | 5.50 | 1,226.50 |
| 2 | 4 | 13.50 | 0.00275 | 60.00 | 223.00 | -5.50 | -1,226.50 |
| Section geometry | |
| Section | 16 × 16 in (rectangular) |
| Ag (gross area) * | 256.0 in² |
| Ast (total steel area) * | 8.00 in² |
| ρ (reinforcement ratio) * | 0.0312 (3.12%) |
| Materials | |
| f′c | 5,000 psi |
| fy (longitudinal) | 60 ksi (Grade 60) |
| Concrete | Normal weight |
| Reinforcement | |
| Longitudinal bars | 8-#9 |
| Per-face distribution | 2 per b-face, 0 per h-face (+ 4 corners) |
| Clear cover | 1.561 in |
| Transverse | #3 ties @ 12 in |
| Loads | |
| Pu | 300 kip |
| M2 (larger end moment) | 0.5 kip-ft |
| M1 (smaller end moment) | 0 kip-ft |
| Curvature | Single |
| Bending axis | X |
| Transverse load between supports | No |
| Slenderness parameters | |
| Lu (unsupported length) | 120 in (10.00 ft) |
| k (effective length factor) | 1 |
Assumptions and limits
- Tie arrangement and crossties (§25.7.2.3) are not checked.
Pro tier · in development
More capabilities are on the way as calcnote grows. Pricing under discussion; help shape it.
Download
Same calc note in either format.
Tell us what worked (or didn't)
calcnote is in active development. What would make this output more useful for your work? What's missing? What looked wrong? Short or long, we read every reply.
Verdict method 8 · build 40c109d · generated 2026-10-23 00:14 UTC