---
title: "Repair versus retrofit; configuration factors"
subject: "Building Technology"
chapter: 11
key: "semester_6/building_technology:retrofit-vs-repair-config"
source: https://www.bctengineer.com/q/semester_6/building_technology/retrofit-vs-repair-config
site: BCT Engineering
---

# Repair versus retrofit; configuration factors

Building Technology · Chapter 11: Earthquake protection & Retrofitting in building

- Asked in: 2080 Chaitra, 1+4 marks
- Video: [Repair, Rehabilitation and Retrofitting of structure](https://www.youtube.com/watch?v=xvjmvNUcX00) — CiViL PEdiA
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/building_technology/retrofit-vs-repair-config
- Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-11

## Question

Differentiate between repair and retrofit. What are the various configuration factors that should be considered for improving seismic safety of building?

## Short answer

Repair restores original condition; retrofit improves seismic capacity beyond original. Configuration factors for seismic safety include a simple rectangular plan with length:width ≤3, symmetrical mass and stiffness, regular elevation without soft storeys, light weight, limited openings, seismic gaps, and a continuous load path with strong foundation.

## Answer

#### Repair versus retrofit
| Basis | Repair | Retrofit |
|---|---|---|
| Purpose | Bring a damaged building back to its original condition | Improve the seismic strength beyond the original |
| Scope | Local damage only | Overall system, members and connections |
| Examples | Crack filling, replastering | Jacketing, shear walls, bracing |

#### Configuration factors for seismic safety
#### 1. Simple, symmetrical plan
Square or rectangular plans resist earthquakes best. Irregular shapes (L, T, U, H) twist and concentrate stress at re-entrant corners; where such shapes are needed, separate them into rectangular blocks with seismic joints.

#### 2. Plan aspect ratio
Length : width should not exceed about 3. Long buildings receive different ground motion at the two ends and develop large diaphragm stresses.

#### 3. Symmetry of mass and stiffness
The centre of mass and the centre of rigidity should coincide to avoid torsion. Place stiff walls and cores symmetrically.

#### 4. Regular elevation and avoiding a soft storey
Avoid sudden changes in stiffness, mass or strength along the height (open ground storey, set-backs, heavy top floor). Walls and columns should be continuous from foundation to roof.

#### 5. Light weight and low height
Earthquake force is proportional to mass, so use a light roof and floors, keep the centre of gravity low, and limit the number of storeys.

#### 6. Openings in walls
Openings should be small and centrally placed, away from corners: total openings not more than about 50% of the wall length in a storey, and not closer than about 0.5 m (or one-fourth of the wall height) to a corner.

#### 7. Seismic gap
Adjacent buildings should be separated by a gap (about 15-30 mm per storey as per IS 4326, depending on the structural system, and more in high seismic zones) to avoid pounding.

#### 8. Strong foundation and continuous load path
Use the same foundation type and depth throughout, tie the structure with a plinth band or tie beams, and provide a rigid diaphragm to transfer loads to the walls.

## Check yourself

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

1. Which pair is correct?
   A. Repair: local damage only; Retrofit: overall system, members and connections
   B. Repair: overall system; Retrofit: local damage only
   C. Both address only local cracks
   D. Repair improves strength beyond original
   Answer: A. Repair is local; retrofit is system-wide strengthening. (Key point: Repair vs retrofit scope)

2. What avoids torsion?
   A. Centre of mass far from centre of rigidity
   B. Centre of mass and centre of rigidity coincide
   C. Stiff walls placed on one side
   D. Irregular L-shaped plan
   Answer: B. Coincident centres of mass and rigidity avoid twisting. (Key point: Torsion)

3. Why use a light roof/floor and low height?
   A. Light materials are cheaper only
   B. Earthquake force is inversely proportional to mass
   C. Earthquake force is proportional to mass
   D. Height has no effect
   Answer: C. Seismic force = mass x acceleration, so lighter and lower is safer. (Key point: Weight)

4. What is the purpose of a gap between adjacent buildings?
   A. Allow extra openings
   B. Reduce foundation depth
   C. Support the roof
   D. Avoid pounding
   Answer: D. A seismic gap lets buildings sway without hitting each other. (Key point: Seismic gap)

## Related in Building Technology

- [Configuration factors for seismic safety](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aconfig-factors-seismic) — Building Technology, chapter 11, asked 2×
- [Retrofit versus repair; column jacketing](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aretrofit-vs-repair-jacketing) — Building Technology, chapter 11

## Related in other subjects

- [Improving seismic performance of masonry](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aseismic-performance-improvement) — Concrete Technology and Masonry Structure, chapter 9
- [Seismic base shear of a masonry building](https://www.bctengineer.com/question.md?key=semester_5%2Fdesign_of_timber_and_masonry_structures%3Abase-shear-two-storey-masonry-building) — Design of Timber and Masonry Structures, chapter 7