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structural / flexure

Elastic bending stress calculator.

Compare an applied bending moment with an elastic section modulus and an entered allowable bending stress. The result is a transparent M/Z screen, not a code-compliant member design.

read the result

Stress is moment divided by section modulus.

For a known elastic section modulus Z, the extreme-fibre bending stress follows the simple relationship σ = M/Z. CivilKit keeps the moment, section modulus, allowable stress, and utilisation visible so the first-pass result can be checked without hiding the unit conversion.

Governing equations

σ = M/Z; Mallow = fbZ; and Zrequired = M/fb. With M in kN·m and Z in cm³, the stress conversion used here is σ = 1000M/Z in MPa.

The basic flexural relationship is also shown as f = M/S in this FHWA bridge design example. The entered allowable stress remains the responsibility of the user and must have a clear material, code, and load-combination basis.

Keep it as a screen.

  • Lateral-torsional buckling, local buckling, shear interaction, axial force, torsion, fatigue, and deflection are not checked.
  • Section classification, effective properties, holes, openings, composite action, reinforcement, and connection resistance are not included.
  • Load factors, resistance factors, material strength, national annexes, and serviceability criteria are not selected by this calculator.