---
title: "Elastic wave tomography and push shear tests"
subject: "Concrete Technology and Masonry Structure"
chapter: 10
key: "semester_5/concrete_technology_and_masonry_structure:elastic-wave-tomography-push-shear"
source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/elastic-wave-tomography-push-shear
site: BCT Engineering
---

# Elastic wave tomography and push shear tests

Concrete Technology and Masonry Structure · Chapter 10: Testing of masonry elements

- Asked in: 2075 Ashwin, 2+2 marks
- Video: [Elastic Wave Tomography 🔥](https://www.youtube.com/watch?v=fI9LVE5OCrs) — DIPAK  MANDAL
- 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/elastic-wave-tomography-push-shear
- Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-10

## Question

Explain with neat sketches the elastic wave tomography test and push shear test for masonry structures.

## Short answer

Elastic wave tomography uses transmitted stress waves between a grid on opposite faces, inverting travel times to a velocity tomogram; low-velocity areas indicate internal defects. The push-shear test pushes a brick along its bed joints, giving τ = F/(2Ab) and cohesion c = τ - μσv (μ ≈ 0.4-0.65).

## Answer

#### Elastic wave (sonic) tomography

**Principle:** elastic (stress) waves travel faster in sound, dense masonry and slower through voids, cracks and moisture. The travel time between many source and receiver positions is measured and processed to give a velocity image (a tomogram) of the wall interior.

**Procedure**

1. Mark a grid of points on both faces of the wall (e.g. every 0.25 to 0.5 m).
2. A small instrumented hammer (or piezo transmitter) at one point generates a pulse; accelerometers or receivers at other points record the arrival time $t$.
3. Velocity along each path $v = d/t$ ($d$ path length). Many crossing paths are collected.
4. Software (inversion, e.g. SIRT) divides the wall into cells and solves for a velocity in each cell, giving a colour map.
5. **Interpretation:** low-velocity zones are voids, cracks or moist or weak masonry; high velocity means sound masonry. Used to detect internal damage, repairs and leaf separation without damaging the wall.

```text
 Transmitter (hammer)        Receivers
  T o ----------> o R1       Wall section grid
    o ----------> o R2       paths cross the wall;
    o ----------> o R3       slow zone = void or crack
```

#### Push shear test

An in-situ test of the shear strength of bed joints. A brick is freed by removing the vertical joints on both sides (one brick removed to fit a jack), then pushed horizontally with a hydraulic jack until it slides. Shear strength $\tau=F/(2A_b)$ and cohesion $c = \tau-\mu\sigma_v$, with $\mu\approx0.4$ to $0.65$ and $\sigma_v$ the vertical compressive stress on the joint.

```text
 +----+----+----+
 |    |[jack]->[brick]|    F slides the brick
 +----+----+----+
```

## Check yourself

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

1. Why do waves reveal damage in tomography?
   A. Waves travel slower through voids, cracks and moisture than through dense masonry
   B. Waves travel faster in voids
   C. Wave speed is constant
   D. Colour changes
   Answer: A. Velocity differences map interior condition. (Key point: Principle)

2. How is velocity along a path computed?
   A. v = d/t
   B. v = t/d
   C. v = F/A
   D. v = d x t
   Answer: A. Path length divided by travel time. (Key point: Velocity)

3. What does a low-velocity zone on the tomogram mean?
   A. Void, crack or moist/weak masonry
   B. Sound masonry
   C. Steel bar
   D. A new repair
   Answer: A. High velocity indicates sound masonry. (Key point: Interpretation)

4. Push shear gives which result?
   A. tau = F/(2A_b) and c = tau - mu sigma_v
   B. Elastic modulus
   C. Wave velocity
   D. Stress by cancellation pressure
   Answer: A. Shear strength of bed joints and cohesion. (Key point: Push shear)

## Related in Concrete Technology and Masonry Structure

- [Push shear test of masonry](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Apush-shear-test) — Concrete Technology and Masonry Structure, chapter 10, asked 2×
- [Flat-jack and push-shear tests](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aflat-jack-and-push-shear) — Concrete Technology and Masonry Structure, chapter 10, asked 2×
- [Diagonal shear and push shear tests](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Adiagonal-shear-push-shear) — Concrete Technology and Masonry Structure, chapter 10, asked 6×
- [Compressive and diagonal shear tests of masonry](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Acompressive-diagonal-shear-tests) — Concrete Technology and Masonry Structure, chapter 10, asked 2×
- [Diagonal shear test of masonry wall](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Adiagonal-shear-test) — Concrete Technology and Masonry Structure, chapter 10, asked 6×
- [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×

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- [Diagonal shear test and flat-jack test calculations](https://www.bctengineer.com/question.md?key=semester_5%2Fdesign_of_timber_and_masonry_structures%3Adiagonal-shear-flat-jack-numerical) — Design of Timber and Masonry Structures, chapter 8
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