Concrete & Rebar Calculator — Axial + Bending with Slenderness
Screen basic column axial capacity, slenderness, simplified second-order effects, and rebar weight in one place. It is a practical estimator, not a substitute for full design checks. Tiny gremlin disclaimer, but an honest one.
1) Project & Design Settings
For final design, use full code procedures for axial load–moment interaction, sway/non-sway classification, magnification, creep, minimum eccentricity, detailing, and ductility provisions.
2) Concrete Elements
| Type | L (m) | W (m) | H (m) | Qty | K | M (kN·m) | Grade | Waste % | Cover (mm) | Ø (mm) | Bars | Pu (kN) | λ | δ | Screening Status | Action |
|---|
Simplified axial/slenderness screening is applied only to Column and Tie Column rows. Other concrete rows remain quantity calculations only. For members beyond the screen, the calculator shows magnified moment guidance rather than a full interaction design.
3) Rebar Schedule (Weight-Only)
| Ø (mm) | Len (m) | Qty | Action |
|---|
4) Final Calculation Dashboard
Calculate concrete rows to view quantity distribution and allowance impact.
Calculate rebar rows to view diameter-wise steel distribution.
The full report bundles project metadata, input summary, KPI cards, segment subtotals, formulas, assumptions, applied allowances, and step-by-step calculation traces. No mystery math goblins allowed.
5) Full Calculation Report Preview
Run the calculations, then generate the full report to preview all metadata, steps, subtotals, assumptions, formulas, and reference basis here.
What This Calculator Can Do • How It Works • How to Use It
Your standards‑aware screening tool for axial + bending checks with slenderness, plus a quick rebar weight estimator and neat reports.
What This Calculator Can Do
- Code presets: switch among IS 456, ACI 318, and Eurocode 2; steel grade options update automatically.
- Element library: Slab, Beam, Column, Footing, and more — auto‑populate typical dimensions and reinforcement counts to get you started.
- Slenderness screen: computes KL/r and flags Short or Slender for a quick reality check.
- Second‑order hint: shows a simplified magnification factor
δ = 1 / (1 - Pu/Pcr)(capped for stability) and the magnified moment readout. - Rebar weight: quick schedule for total length & mass — handy for procurement and logistics.
This is a screening & estimation tool. Final design must follow full code procedures and project specifications (moment magnification, sway checks, creep/shrinkage, crack & deflection control, durability, detailing, etc.).
How It Works — Under the Hood
Axial Resistance (screening)
Pu ≈ 0.40·fck·Ag + 0.67·fy·As (kN, with MPa → kN/m²). Short column if KL/r ≤ 12 (screen). Elastic modulus: Ec ≈ 5000√fck MPa.
Slenderness & Magnification
r ≈ b/√12 (minor axis), KL = K·H, Euler: Pcr = π² Ec I / (KL)² using I = A·r². Magnification: δ = 1/(1 - Pu/Pcr) (capped & for guidance only).
Axial Resistance (tied columns)
Pn ≈ 0.85·f′c·(Ag − As) + fy·As, Pu = φ·Pn with φ ≈ 0.65. Nonsway/slenderness screening ~ KL/r ≤ 22 (project‑specific). Ec ≈ 4700√f′c MPa.
Second‑Order
Displays a simplified δ using Euler‑based Pcr for awareness; full moment magnification per ACI depends on end moments, sway condition, creep, etc.
Design Strengths
fcd = αcc·fck/γc, fyd = fy/γs, Pu ≈ fcd·Ac + fyd·As. Screening slenderness ~ KL/r ≤ 20 (varies). Ec ≈ 22,000·((fck+8)/10)0.3 MPa.
Stability
Euler‑based Pcr readout is informational; full EC2 second‑order checks depend on imperfection factors, creep coefficient, end moments, and member class.
How to Use It (Step‑by‑Step)
- Open Design Settings and choose your Design Code (IS/ACI/EC2) and Steel Grade. Click ↻ Load Code Defaults to auto‑populate.
- In Concrete Elements, click + Add Element or + Sample Set. Pick an element type to auto‑fill typical dimensions.
- Enter K, member height H, and any applied moment M (kN·m). Adjust cover, bar diameter and number of bars if needed.
- Hit 📊 Calculate. The table shows: axial capacity Pu, slenderness λ = KL/r, magnification δ, and status (OK/SLENDER).
- Generate a neat 📝 Report or export ⬇️ CSV for records.
- Use Rebar Schedule (Weight‑only) to tally lengths and total mass for procurement. Export its report/CSV too.
Pro Tips & Assumptions
- Cross‑section axes assumed rectangular;
r ≈ b/√12(minor axis) for screening. - Magnification uses Euler
PcrwithI = A·r², informational only. - Concrete strength uses fck (IS/EC2) or f′c (ACI) as selected; units internally in kN and MPa.
- Rebar weight:
W(kg) = 0.006165 × d² × L × Qtywithdin mm,Lin m.
- Start with the Sample Set to sanity‑check your K factors and heights.
- Batch your scenarios: duplicate rows with different K or M to see trends before detailed design.
- Attach the exported CSV to your IFT/IFC submittals for traceability.
FAQ
No. It’s for screening & estimation. Use full code procedures and the project’s structural model for final design.
Yes — in the main calculator choose the US/metric mode where applicable; internally # sizes map to equivalent diameters for weight math.
Absolutely. Pick an element type to load defaults, then overwrite any field. Your inputs drive the calculations.
