- 2074 Chaitra · 2+4 marks
In-plane, out-of-plane; ductile behaviour
Short answer
In-plane: strong but fails by sliding, diagonal shear, or rocking. Out-of-plane: weak, fails by overturning or bending. Unreinforced masonry is brittle with minimal ductility; reinforced/confined masonry provides ductile plateau and energy dissipation through steel yielding.
Describe the in-plane and out-of-plane behaviour of masonry structures. Explain ductile behaviour of reinforced and unreinforced masonry structure.
In-plane and out-of-plane behaviour
- In-plane: force acts parallel to the wall; the wall is a shear wall that develops its shear strength and fails by sliding, diagonal tension (X-cracks) or rocking and toe crushing. The behaviour is relatively stiff and strong.
- Out-of-plane: force acts perpendicular to the wall; the wall bends as a vertical or two-way plate. It has little tensile strength, so it fails by overturning, horizontal mid-height cracking, or vertical corner cracks. This is the weaker and more dangerous direction.
Ductile behaviour
Ductility is the ability to deform plastically without losing strength, giving warning and absorbing energy.
- Unreinforced masonry (URM): brittle. After the first cracks the strength falls sharply; very small ductility (displacement ductility about 1 to 2) and low energy dissipation, so collapse is sudden. Some limited ductility is shown by rocking walls.
- Reinforced masonry (RM) / confined masonry: steel bars in cores or RCC bands and tie columns carry tension and shear after the masonry cracks. The load-displacement curve has a long plateau with large deformation (ductility about 3 to 5), cracks are spread, and energy is dissipated.
Load
| ____ RM (ductile plateau)
| /
| / \
| / URM \_____ sudden drop
| /
+------------------- Displacement
Hence reinforcing or confining the masonry converts the sudden brittle failure into a ductile one and greatly improves earthquake performance.
✓ Answer checked by Claude Opus 5.5 (high effort)
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