Calculate maximum bending stress using the flexure formula σ = My/I. Verify structural members against material yield strength.
Enter the maximum bending moment acting on the section and the distance from the neutral axis to the extreme fiber (y).
Input the Moment of Inertia (I). The tool uses the flexure formula: σ = My/I to calculate the maximum normal stress in the member.
Compare the resulting stress to the yield strength of your material (e.g., 250 MPa for A36 steel) and apply a safety factor (typically 1.5 to 2.0).
Normal bending stress is zero at the neutral axis (center) and reaches its maximum at the extreme top and bottom surfaces of the beam.
Elastic stress allows the beam to return to its original shape. Plastic stress occurs when the material yield strength is exceeded, causing permanent deformation.
Section Modulus is defined as I/y. Bending stress can be simplified as σ = M/S. Using S is standard for selecting steel members from catalogs.
Compute σ = M/S from the design moment, then compare it to the allowable stress — the yield strength divided by a safety factor (for A36 steel, 250 MPa ÷ 1.5 ≈ 167 MPa allowable). If the calculated stress exceeds the allowable value, increase the section modulus by choosing a deeper or heavier member rather than a stronger material, since stiffness usually governs first.