In a beam under bending (for sagging bending), where is the maximum compressive strain observed?

Question

Question

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RRB JE CBT 2 (Civil Engineering) ReExam Official Paper (Held On: 04 Jun, 2025)

Answer 1

Explanation:

In sagging, the top fibres are pushed inward, experiencing compression.
The topmost fibre is furthest from the neutral axis, and therefore experiences the maximum compressive strain.
The bottom fibres are stretched outward, hence they are in tension.
The bottommost fibre has the maximum tensile strain, opposite in nature but equal in magnitude (in elastic bending) to the compressive strain at the top.
Located between the top and bottom fibres where strain and stress are zero.
It separates the compression zone (above) and the tension zone (below).
The strain varies linearly across the depth of the beam section in elastic bending.
Maximum at the top and bottom, and zero at the neutral axis.

Additional Information

Bending refers to the deformation of a beam when an external load or moment is applied perpendicular to its longitudinal axis.
The internal resistance developed in response to this load causes the beam to bend, resulting in internal stresses and strains within the material.
The cross-section of the beam experiences compressive stress on one side and tensile stress on the other.
There is a line/plane across the cross-section called the Neutral Axis, where bending stress is zero.
The magnitude of stress increases linearly from the neutral axis to the outermost fibres.
Beams can fail in bending when maximum stress exceeds the material strength (either tensile or compressive).
Overloaded beams can crack, deform permanently, or collapse.