Bending of beams

What this module covers

• Explain why bending produces tension on one face and compression on the other
• Locate the neutral axis and say what happens there
• Use the flexure formula to find bending stress
• Explain what second moment of area and section modulus really mean
• Say why an I-section is efficient and where simple bending theory stops

Lessons

1. 9.1

   Why bending causes stress

   Curvature, the neutral axis, and the linear stress distribution.

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2. 9.2

   Deriving the bending formula

   Building σ = My/I from geometry, Hooke's law and equilibrium — not quoting it.

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3. 9.3

   Second moment of area and section modulus

   The flexure formula, and what makes one section better than another.

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4. 9.4

   Combined bending and axial load

   Adding two stress distributions, and the point where tension disappears.

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5. 9.5

   Plastic bending and the plastic hinge

   What a ductile section can still do after its extreme fibre has yielded.

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6. 9.6

   Unsymmetrical bending and principal axes

   What happens when the section has no axis of symmetry, and the beam refuses to bend the way you pushed it.

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