How much moment can this concrete beam carry? Set the section, steel, and material strengths to see the compression block form and the capacity compute.
Reinforced Concrete BeamLive
flexural capacity (ACI)
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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.
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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How it works
A reinforced concrete beam in bending balances a compression block in the concrete against tension in the steel. Equating those forces gives the stress-block depth a, and the nominal moment capacity is Mn = As·fy·(d − a/2). A tension-controlled section, where the steel yields before the concrete crushes, fails in the ductile manner codes require. Educational tool, not a design.
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