Core or Kernel of Section MCQ with answer and solution

Concept

Self-weight gives compressive direct stress that cancels tension from wind bending, so the chimney stays stable.

Formula

σ = W/A ± M/Z; no tension if W/A ≥ M/Z

Step-by-step solution

1. Wind pressure gives a bending moment M at the base of the chimney. 2. Bending gives tension on the windward side and compression on the leeward side. 3. Masonry is weak in tension, so tension must be avoided. 4. Self-weight W gives direct compressive stress W/A over the whole section. 5. If W/A ≥ M/Z, there is no tension. So self-weight gives stability.

Explanation

Masonry cannot take tension. Wind tries to bend and overturn the chimney. The direct compressive stress from the chimney's own weight cancels the bending tension and keeps the chimney stable.

Why the other options are wrong

A: Earthquake tensile stress is a destabilising effect, not a stabilising one. B: Wind bending stress causes tension and overturning, so it reduces stability. D: Wind shear stress is small and also acts against stability.

Shortcut

Stability comes from the stress that resists overturning, and that is self-weight.

Common mistake

Choosing wind bending stress because it is the main design load, but it is a destabilising stress.