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For Educators · Concrete Beam

Concrete Beam for a roof rafter

Built for educators teaching it to a class. Drop a live demo into a lecture or assign it as a shareable link — no lab installs. Simulate a roof rafter live below — adjust the inputs and watch it respond, right in your browser.

Reinforced Concrete BeamLive

flexural capacity (ACI)

Controls

Presets

Width b (mm)

Effective depth d (mm)

Steel area As (mm²)

Concrete f'c (MPa)

Steel fy (MPa)

A reinforced concrete beam resists bending through a compression block in the concrete and tension in the steel. Setting these forces equal gives the stress-block depth a, and the moment capacity Mn = As·fy·(d − a/2). A tension-controlled section (steel yields first) fails gradually — the ductile behavior codes require. Educational tool, not a design.

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Data Inspector

Stress block a82 mm

Nominal Mn289 kN·m

Design φMn260 kN·m

Behaviortension-controlled

Governing equation

a = \frac{A _{s} f _{y}}{0.85 f _{c}^{'} b} = 82 mm, M_{n} = A_{s} f_{y} (d - \frac{a}{2}) = 1500 \cdot 420 (500 - \frac{82}{2}) = 289 kN\cdotm

Reading this result: Tension-controlled: with ρ ≈ 0.0100 well under 0.75·ρ_bal the steel yields first and the beam warns before it fails, while Mn = As·fy·(d − a/2) rises almost linearly with steel here.

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Frequently asked questions

Is this good for educators?: Yes — this version of "Concrete Beam for a roof rafter" is framed for educators teaching it to a class. Drop a live demo into a lecture or assign it as a shareable link — no lab installs.
Do I need to install anything?: No. It runs in any modern browser, free, with no account required.