Reinforced Concrete Beam Section Designer — ACI 318M-11
A complete section designer for reinforced concrete beams — go beyond simple ɸM_n: get the section drawing, strain diagram, and required A_s in one shot.
Formulas
| Quantity | Formula |
|---|---|
| Strain compatibility (linear) | ε_s = 0.003 · (d − c) / c |
| Equilibrium of forces | 0.85 · f'_c · a · b = A_s · f_s − A'_s · f'_s |
| Nominal moment (with compression steel) | M_n = 0.85·f'_c·a·b·(d − a/2) + A'_s · f'_s · (d − d') |
How to use it
- Enter b, h, cover, f'_c, f_y, and the bar arrangement.
- The tool draws the section, computes a, c, and ε_t.
- Read ɸM_n and compare with M_u.
- Add compression bars if the section is over-reinforced.
Frequently Asked Questions
Why ACI 318M-11 and not 318-19?
The interactive designer was originally calibrated to ACI 318M-11. The same equilibrium and strain compatibility apply in 318-19; only the strength-reduction factor and minimum-strain thresholds shifted slightly.
Does it support T-beams?
Yes — switch the cross-section type to T or L.