declared calculation basis
Keep the force couple visible.
This page uses the first-generation EN 1992-1-1:2004 + AC:2010 + A1:2014 basis. The implementation is limited to normal-weight concrete with 20 ≤ fck ≤ 50 MPa, bonded tension steel only, no axial force, and an undisturbed beam region.
Clauses and equations
EN 1992-1-1 §3.1.6, Expression 3.15:
fcd = αcc fck / γc · fyd = fyk / γsUnder §3.1.7(3), Expressions 3.19 and 3.21, the rectangular block factors for this page are λ = 0.8 and η = 1.0. Equilibrium and the internal lever arm are evaluated as:
x = As fyd / (ηλb fcd) · z = d - λx/2 · MRd = As fydzHere x is neutral-axis depth, z is the internal lever arm, b is the compression width, d is the effective depth, and As is the provided bonded tension-steel area. EN 1992-1-1 §6.1 requires plane sections, compatible bonded-steel strain, ignored concrete tension, and concrete compression stresses from §3.1.7.
Yielded-steel boundary
The simplified equilibrium expression is accepted only when the tension steel reaches its design yield strain:
εyd = fyd/Es · εs = εcu2(d-x)/x · require εs ≥ εydFor this range, εcu2 = 3.5‰. If the check fails, the page reports a review condition instead of treating the yielded-steel equation as valid.
What this page does not check
- Minimum or maximum reinforcement, bar spacing, anchorage, laps, curtailment, cover, or execution under §8–§9.
- Shear, torsion, bearing, discontinuity regions, strut-and-tie action, fire, durability, crack width, deflection, or other SLS checks.
- Compression reinforcement, axial force, biaxial bending, prestressing, T-sections, second-order effects, or lateral instability.
- EN 1990 actions/combinations, EN 1991 loading, and project-specific National Annex selection.