---
title: "Reinforced and unreinforced masonry; rat-trap bond"
subject: "Concrete Technology and Masonry Structure"
chapter: 7
key: "semester_5/concrete_technology_and_masonry_structure:reinforced-unreinforced-rat-trap"
source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/reinforced-unreinforced-rat-trap
site: BCT Engineering
---

# Reinforced and unreinforced masonry; rat-trap bond

Concrete Technology and Masonry Structure · Chapter 7: Introduction to masonry structures

- Asked in: 2072 Chaitra, 6 marks
- 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/reinforced-unreinforced-rat-trap
- Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-7

## Question

Define reinforced and unreinforced masonry structure. Explain with neat sketch the rat-trap bond and mention its advantages.

## Short answer

Unreinforced masonry uses only units and mortar, relying on compressive strength with low tensile capacity. Reinforced masonry incorporates steel bars in cores or bed joints to resist tension and shear. Rat-trap bond places bricks on edge forming a cavity wall, saving about 25% bricks, giving thermal insulation, and reducing weight.

## Answer

#### Unreinforced masonry (URM)

A masonry structure built of units and mortar only, with no steel bars in the walls. Its strength comes from the compressive strength of the masonry; its tensile and shear capacity is small. Load-bearing brick or stone buildings that have, at most, RCC bands (as in IS 1905 / NBC 109) are of this type.

#### Reinforced masonry (RM)

Masonry in which steel bars (vertical bars in the cores or pockets of blocks, horizontal bars in bed joints, or RCC bands and tie columns) are provided to carry tension, shear and flexure and to give ductility. It resists earthquakes and wind better and allows larger openings and taller walls.

#### Rat-trap bond

Bricks are laid on edge, with stretchers on the faces and headers across the wall at regular intervals, leaving a cavity inside the wall. The wall is usually 230 mm thick, with a cavity about 110 to 120 mm wide.

```text
Plan, alternate courses        Elevation
1: |##|  |##|  |##|           ____ ____ ____ ____
   |##############|           |____|____|____|____|
   |##############|           |_|__|_|__|_|__|_|__|
2: |##############|           |____|____|____|____|
   |   cavity     |
   |##############|
```

#### Advantages

- Saves about 25 percent of bricks and 10 to 15 percent of mortar, so it is economical.
- Good thermal insulation and dampness resistance because of the cavity.
- Lighter wall, so a smaller load on the foundation.
- Pleasing face; plaster is not essential.

## Check yourself

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

1. What is unreinforced masonry?
   A. Masonry with vertical bars in cores
   B. Masonry of units and mortar only, with no steel bars in the walls
   C. Masonry with horizontal bars in bed joints
   D. Only RCC walls
   Answer: B. In URM strength comes from compression and tensile and shear capacity is small. (Key point: URM)

2. What does steel do in reinforced masonry?
   A. Carries tension, shear and flexure and gives ductility
   B. Only reduces weight
   C. Replaces mortar
   D. Gives thermal insulation
   Answer: A. Reinforcement improves earthquake and wind resistance. (Key point: RM)

3. How is a rat-trap bond wall built?
   A. Solid flat bricks
   B. Hollow concrete blocks
   C. Bricks on edge, stretchers on faces and headers across, leaving a cavity
   D. Stone rubble
   Answer: C. The wall is about 230 mm with a cavity of brick thickness. (Key point: Rat trap)

4. Which saving is correct for rat-trap bond?
   A. About 5% bricks
   B. About 50% mortar
   C. About 25% steel
   D. About 25% bricks and 10 to 15% mortar
   Answer: D. The cavity reduces material. (Key point: Savings)

## Related in Concrete Technology and Masonry Structure

- [Rat-trap bond and its advantages](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Arat-trap-bond-advantages) — Concrete Technology and Masonry Structure, chapter 7
- [Brick bond types; rat-trap bond merits and demerits](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Abond-types-rat-trap-pros-cons) — Concrete Technology and Masonry Structure, chapter 7
- [English and rat-trap bonds](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aenglish-rat-trap-bond) — Concrete Technology and Masonry Structure, chapter 7
- [Use of masonry; types of brick bond](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Amasonry-uses-bond-types) — Concrete Technology and Masonry Structure, chapter 7, asked 2×
- [Use of masonry; English and Flemish bond](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Amasonry-use-english-flemish) — Concrete Technology and Masonry Structure, chapter 7
- [Closers in brick masonry; English and Flemish bond](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aclosers-english-flemish-bond) — 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