---
title: "Ductile behaviour of reinforced and unreinforced masonry"
subject: "Design of Timber and Masonry Structures"
chapter: 6
key: "semester_5/design_of_timber_and_masonry_structures:ductility-reinforced-unreinforced-masonry"
source: https://www.bctengineer.com/q/semester_5/design_of_timber_and_masonry_structures/ductility-reinforced-unreinforced-masonry
site: BCT Engineering
---

# Ductile behaviour of reinforced and unreinforced masonry

Design of Timber and Masonry Structures · Chapter 6: Masonry Structures Under Lateral Loads

- Asked in: year not given, 6 marks
- Video: [lecture-10-Behaviour of masonry buildings- structural engineering](https://www.youtube.com/watch?v=27rll5DWSAQ) — MOHAMMEDABBAS JAMANI
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/design_of_timber_and_masonry_structures/ductility-reinforced-unreinforced-masonry
- Whole chapter: https://www.bctengineer.com/md/semester_5/design_of_timber_and_masonry_structures/chapter-6

## Question

Explain the ductile behaviour of reinforced and unreinforced masonry structures. How can the ductility of masonry be improved?

## Short answer

URM is brittle (ductility ~1–1.5); RM yields steel after cracking, giving ductile flexural failure. Improve ductility with vertical/horizontal reinforcement, RC bands, bed-joint steel, and box action.

## Answer

**Ductility** is the ability of a structure to undergo large inelastic deformation without significant loss of strength before collapse. It is measured by the displacement ductility $\mu = \Delta_u/\Delta_y$, the ratio of ultimate to yield displacement.

#### Unreinforced masonry (URM)
- Masonry units and mortar are brittle with low tensile strength. After first diagonal cracking or toe crushing, strength drops quickly.
- Typical failure modes (diagonal shear, sliding, out-of-plane collapse) are brittle with small energy dissipation and ductility close to 1–1.5.
- URM can show limited ductility by rocking of squat walls under low axial load, but this is unreliable.

#### Reinforced masonry (RM)
- Vertical reinforcement in cells or cavities (grouted) and horizontal reinforcement in bond beams or bed joints carry tension after the masonry cracks.
- A flexural failure with yielding of steel is preferred to shear failure. Walls then show a wide hysteresis loop, absorb energy and can sustain large displacement.
- Shear failure remains brittle unless enough horizontal steel is given; the design should force flexure to govern ("strong shear, weak flexure").

```text
 Load
  |       /\                URM: peak, then sudden drop
  |      /  \
  |     /    \____
  |    /   ________________ RM: ductile plateau
  |   /  _/
  |  / _/
  | /_/
  |/_____________________ Displacement
```

#### Confined masonry
Masonry walls enclosed by RC tie-columns and tie-beams cast after the wall are not reinforced masonry, but they show better ductility: the frame confines the wall after cracking and prevents collapse.

#### Improving ductility
1. Provide reinforced concrete or timber bands (plinth, lintel, roof) to tie the walls and control cracks.
2. Use vertical bars at corners, junctions and sides of openings, anchored in the foundation and the roof band.
3. Use bed-joint reinforcement or steel mesh; grout hollow blocks.
4. Use good bond between units and mortar, and avoid weak mortar or dry stone.
5. Keep walls at low axial stress, and limit slenderness and opening size.
6. Ensure box action by rigid floor diaphragms and tied roofs.

The code reduction (response reduction) factor $R$ is higher for reinforced masonry than for URM because of this ductility.

## Check yourself

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

1. How is displacement ductility defined?
   A. mu = yield displacement / ultimate displacement
   B. mu = ultimate displacement / yield displacement
   C. mu = ultimate load / yield load
   D. mu = stiffness / mass
   Answer: B. Ductility is the ratio of ultimate to yield displacement, mu = delta_u / delta_y. (Key point: Definition of ductility)

2. How does unreinforced masonry behave after first cracking?
   A. Strength is retained with large deformation
   B. Ductility is above 5
   C. Steel yields and absorbs energy
   D. Strength drops quickly with brittle failure and ductility of about 1-1.5
   Answer: D. Brittle units and mortar with low tensile strength give sudden loss of strength and small ductility. (Key point: URM behaviour)

3. What failure should reinforced masonry be designed for?
   A. Flexural yielding of steel, avoiding brittle shear (strong shear, weak flexure)
   B. Shear failure before flexure
   C. Sliding along bed joints
   D. Crushing of units without steel yielding
   Answer: A. Flexural yielding gives wide hysteresis loops and energy dissipation, whereas shear is brittle. (Key point: Reinforced masonry design)

4. Which measure improves ductility of masonry?
   A. Use weak mortar and dry stone
   B. Increase opening sizes
   C. Provide bands, vertical bars at corners and jambs, and rigid diaphragms for box action
   D. Increase axial stress and slenderness
   Answer: C. Bands, vertical bars and tied diaphragms control cracks and prevent brittle collapse. (Key point: Improving ductility)

## Related in Design of Timber and Masonry Structures

- [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

## Related in other subjects

- [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; ductile behaviour](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Ain-out-plane-ductile-behaviour) — Concrete Technology and Masonry Structure, chapter 9
- [Ductile behaviour and how it is induced](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Aductile-behaviour-and-how-it-is) — Design of RCC Structure, chapter 12, asked 2×
- [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×