The 'Navier''s hypothesis' (plane sections remain plane) in beam bending is valid for:
Choose the correct answer
Only steel beams
Slender beams (L/d > 5) — strain varies linearly; NOT valid for deep beams where shear deformation dominates
Only pre-stressed beams
All beams regardless of span/depth ratio
Correct Answer
B. Slender beams (L/d > 5) — strain varies linearly; NOT valid for deep beams where shear deformation dominates
Why is this the answer?
Bernoulli-Navier hypothesis: plane sections remain plane after bending (linear strain variation across depth). Valid for: long beams (span/depth > 5), Euler-Bernoulli beam theory. Fails for: deep beams (d > L/2.5 for UDL, d > L/2 for point load), corbels, connections where shear deformation is significant. IS 456: deep beams need special non-linear analysis.
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