Bending Stress Calculator
Flexural stress σ = Mc/I, section modulus and utilization against an allowable stress.
INPUTS
kN·m
×10⁶ mm⁴
mm
MPa
RESULTS
Bending stress σ = Mc/I
120 MPa
Section modulus S = I/c
333.3 ×10³ mm³
Utilization
72.7 %
Verdict
✓ OK — stress within allowable
How it works
Bending stress varies linearly through the depth: zero at the neutral axis, maximum at the extreme fibres. σ = Mc/I is the flexure formula — the single most used equation in structural design. Since only the extreme fibre matters, engineers work with section modulus S = I/c and check M ≤ S·σallow.
Worked example
M = 40 kN·m on a section with I = 50×10⁶ mm⁴ and c = 150 mm: σ = 40·150/50 = 120 MPa. Against 165 MPa allowable (S275 steel with safety factor) that's 73% utilization — OK.
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