Sample result
Biaxial bending (P-Mx-My): demand-plane angle λ = 33.7 deg
This is a live sample output for a 16×16 in rectangular tied column with 8-#9 longitudinal bars (f′c = 5,000 psi, Grade 60), checked per ACI 318-19 under Pu = 200 kip and M2 = 60 kip-ft. The same section is verified against StructurePoint's published spColumn reference; see the verification pages, the full report (PDF) and the methodology. Run your own column to get an editable .docx calc-note.
Both axial and moment D/C ratios ≤ 1.00.
Demand-plane summary
- λ (demand-plane angle)
- 33.7 deg
- Mx,design
- 150.0 kip-ft
- My,design
- 100.0 kip-ft
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.
3D interaction surface
P-Mx-My capacity envelope (φ-reduced) at 10° cuts. Drag to rotate, scroll to zoom, right-drag to pan. demand point (Pu, Mux, Muy). operating point (φPn, φMnx, φMny).
Interaction Diagram Points (9 anchors, demand-plane cut at λ = 33.7 deg)
| Anchor | Description | c (in) | εt | φ | φPn (kip) | φMλ (kip-ft) |
|---|---|---|---|---|---|---|
| 1 | Pure compression cap | N/A | N/A | 0.65 | 1,123.47 | 0.00 |
| 2 | Cap intersection | 23.83 | -0.00014 | 0.65 | 1,123.50 | 172.56 |
| 3 | Arc strain (zero) (εt = 0) | 22.81 | 0.00000 | 0.65 | 1,069.75 | 198.30 |
| 4 | Arc strain (positive half yield) (εt = +εty/2) | 17.16 | 0.00103 | 0.65 | 677.32 | 299.24 |
| 5 | Compression-controlled limit (εt = εty) | 13.56 | 0.00207 | 0.65 | 369.62 | 310.90 |
| 6 | Transition lower (εt = εty + 0.0015) | 10.34 | 0.00357 | 0.78 | 137.35 | 327.50 |
| 7 | Tension-controlled limit (εt = εty + 0.003) | 8.79 | 0.00469 | 0.87 | 0.00 | 316.82 |
| 8 | Tension-controlled deep (εt = εty + 0.008) | 8.79 | 0.00469 | 0.87 | 0.00 | 316.82 |
| 9 | Pure bending | 8.79 | 0.00469 | 0.87 | 0.00 | 316.82 |
| Quantity | Value |
|---|---|
| Pu (factored axial demand, kip) | 300.00 |
| φPn (axial capacity at operating point, kip) | 508.61 |
| Mu (resultant in the demand plane, Mλ, design moment, kip-ft) | 180.28 |
No transverse load between supports. Cm from end-moment ratio per ACI 318-19 §6.6.4.5.3(a). |
|
| φMλ (moment capacity, kip-ft) | 305.63 |
| c (neutral axis depth, in) | N/A |
| εt (extreme tension strain) | N/A |
| φ (strength reduction factor) | N/A |
| φ regime (§21.2.2) | Compression-controlled φ = 0.65 throughout (εt ≤ εty = 0.00207) |
| D/C axial | 0.58 |
| D/C moment | 0.58 |
| Slenderness (about X) | |
| kl/r about X | 16.67 |
Nonsway frames only (ACI 318-19 §6.6.4.3). For a sway column this result does not apply. |
|
| kl/r limit | 30.00 |
| Slenderness (about Y) | |
| kl/r about Y | 25.00 |
Nonsway frames only (ACI 318-19 §6.6.4.3). For a sway column this result does not apply. |
|
| kl/r limit | 30.40 |
| Tie spacing limit (§25.7.2.1) | 16.00 in (governed by 16·d_bar) |
| Bar clear spacing (§25.2.3) | 2.75 in ≥ 1.50 in |
| Section geometry | |
| Section | 16 × 24 in (rectangular) |
| Ag (gross area) * | 384.0 in² |
| Ast (total steel area) * | 9.48 in² |
| ρ (reinforcement ratio) * | 0.0247 (2.47%) |
| Materials | |
| f′c | 5,000 psi |
| fy (longitudinal) | 60 ksi (Grade 60) |
| Concrete | Normal weight |
| Reinforcement | |
| Longitudinal bars | 12-#8 |
| Per-face distribution | 2 per b-face, 2 per h-face (+ 4 corners) |
| Clear cover | 1.5 in |
| Transverse | #3 ties @ 12 in |
| Loads | |
| Pu | 300 kip |
| M2x (larger end moment, about X) | 150 kip-ft |
| M1x (smaller end moment, about X) | 50 kip-ft |
| Curvature about X | Single |
| M2y (larger end moment, about Y) | 100 kip-ft |
| M1y (smaller end moment, about Y) | 30 kip-ft |
| Curvature about Y | Single |
| Bending | Biaxial (P-Mx-My) |
| Transverse load between supports | No |
| Slenderness parameters | |
| Lu,x (unsupported length, about X) | 120 in (10.00 ft) |
| kx (effective length factor, about X) | 1 |
| Lu,y (unsupported length, about Y) | 120 in (10.00 ft) |
| ky (effective length factor, about Y) | 1 |
Assumptions and limits
- Tie arrangement and crossties (§25.7.2.3) are not checked.
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Verdict method 7 · build bf0b4df · generated 2026-10-19 23:55 UTC