Section Parameters
Beam Width b
mm
Effective Depth d
mm
Tension Steel Area As
mm²
Concrete Strength f'c
MPa
Steel Yield Strength fy
MPa
Steel Area Check
Live readouts (update as load increases)
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Applied moment M [kN·m]
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Neutral axis c [mm]
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Stress block a [mm]
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Concrete stress σc [MPa]
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Steel stress fs [MPa]
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Curvature κ [×10⁻³/m]
Section Strain · Stress Block · Cracking — Live Animation
M/Mn 0%
Compression block
Neutral axis
Tension steel
Cracks
Moment–Curvature (M–κ) Response
Current section
Over-reinforced (brittle, ref.)
Theory & Key Formulas
Whitney stress block depth: $a = \dfrac{A_s f_y}{0.85 f'_c b}$
Neutral axis depth: $c = a / \beta_1$, $\beta_1 = 0.85$ ($f'_c \le 28$ MPa)
Steel strain: $\varepsilon_s = 0.003 \times (d - c)/c$
Nominal moment: $M_n = A_s f_y \left(d - \dfrac{a}{2}\right)$
Design moment: $\phi M_n$, $\phi = 0.90$ ($\varepsilon_s \ge 0.005$)
Yield curvature $\kappa_y=\varepsilon_y/(d-kd)$, ultimate curvature $\kappa_u=\varepsilon_{cu}/c$, ductility $\mu=\kappa_u/\kappa_y$.