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Concrete & Rebar Calculator — Axial + Bending with Slenderness
Screen column capacity, slenderness and basic second‑order effects; estimate rebar weight; export neat reports.
1) Design Settings
Note: This is a screening tool. For final design, use full code procedures (moment magnification, sway checks, creep, etc.).
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 (magn.) | Status |
|---|
3) Rebar Schedule (Weight‑only)
| Ø (mm) | Len (m) | Qty |
|---|
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.
