---
title: "In-plane, out-of-plane; ductile behaviour"
subject: "Concrete Technology and Masonry Structure"
chapter: 9
key: "semester_5/concrete_technology_and_masonry_structure:in-out-plane-ductile-behaviour"
source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/in-out-plane-ductile-behaviour
site: BCT Engineering
---

# In-plane, out-of-plane; ductile behaviour

Concrete Technology and Masonry Structure · Chapter 9: Masonry structures under lateral loads

- Asked in: 2074 Chaitra, 2+4 marks
- Video: [Difference between In Plane and Out of Plane Loading](https://www.youtube.com/watch?v=-O6Vx2IlOEo) — Civil Engineering
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/in-out-plane-ductile-behaviour
- Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-9

## Question

Describe the in-plane and out-of-plane behaviour of masonry structures. Explain ductile behaviour of reinforced and unreinforced masonry structure.

## 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.

## Answer

#### 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.

```text
 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.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is ductility?
   A. Ability to deform plastically without losing strength, giving warning and absorbing energy
   B. Ability to resist high loads elastically
   C. Resistance to cracking
   D. Stiffness
   Answer: A. Ductile structures give warning before collapse. (Key point: Ductility definition)

2. How does unreinforced masonry behave after first cracks?
   A. Long plateau, ductility 3 to 5
   B. Strength falls sharply, ductility about 1 to 2, sudden collapse
   C. Strength rises
   D. Unchanged
   Answer: B. URM is brittle. (Key point: URM behaviour)

3. Why is reinforced or confined masonry ductile?
   A. Bricks are stronger
   B. Mortar is lighter
   C. Steel bars or bands carry tension and shear after masonry cracks
   D. Walls are thicker
   Answer: C. This gives a long plateau and energy dissipation. (Key point: Reinforced masonry)

4. Which direction is weaker and more dangerous?
   A. In-plane
   B. Both equal
   C. Vertical compression
   D. Out-of-plane
   Answer: D. Little tensile strength out-of-plane. (Key point: Direction)

## Related in Concrete Technology and Masonry Structure

- [In-plane and out-of-plane behaviour of masonry](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Ain-plane-out-of-plane-behaviour) — Concrete Technology and Masonry Structure, chapter 9, asked 9×
- [Reinforced and unreinforced masonry; rat-trap bond](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Areinforced-unreinforced-rat-trap) — Concrete Technology and Masonry Structure, chapter 7
- [In-plane, out-of-plane failure and remedial measures](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Ain-plane-out-of-plane-remedial) — Concrete Technology and Masonry Structure, chapter 9
- [Causes and crack patterns of out-of-plane failure](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aout-of-plane-failure-causes) — Concrete Technology and Masonry Structure, chapter 9
- [Uses and scope of masonry structures](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Amasonry-uses-scope) — Concrete Technology and Masonry Structure, chapter 7, asked 5×
- [Advantages of masonry structures](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Amasonry-advantages) — Concrete Technology and Masonry Structure, chapter 7

## Related in other subjects

- [Ductile behaviour of reinforced and unreinforced masonry](https://www.bctengineer.com/question.md?key=semester_5%2Fdesign_of_timber_and_masonry_structures%3Aductility-reinforced-unreinforced-masonry) — Design of Timber and Masonry Structures, chapter 6
- [Seismic behaviour of unreinforced and reinforced masonry](https://www.bctengineer.com/question.md?key=semester_5%2Fdesign_of_timber_and_masonry_structures%3Aseismic-behavior-urm-versus-reinforced) — Design of Timber and Masonry Structures, chapter 7
- [In-plane and out-of-plane behaviour of masonry walls](https://www.bctengineer.com/question.md?key=semester_5%2Fdesign_of_timber_and_masonry_structures%3Ain-plane-out-of-plane-behavior) — Design of Timber and Masonry Structures, chapter 6
- [Out-of-plane bending of a masonry wall](https://www.bctengineer.com/question.md?key=semester_5%2Fdesign_of_timber_and_masonry_structures%3Aout-of-plane-wall-flexure-check) — Design of Timber and Masonry Structures, chapter 6