---
title: "Retrofitting and jacketing"
subject: "Building Technology"
chapter: 11
key: "semester_6/building_technology:retrofit-jacketing"
source: https://www.bctengineer.com/q/semester_6/building_technology/retrofit-jacketing
site: BCT Engineering
---

# Retrofitting and jacketing

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

- Asked in: 2075 Baisakh, 2+6 marks; 2073 Bhadra (asked 2 times)
- Video: [What is Retrofitting Technique ?  Uses of Retrofitting - Types of Retrofitting](https://www.youtube.com/watch?v=46YGCwCaySA) — REINFORCE
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/building_technology/retrofit-jacketing
- Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-11

## Question

How do you define retrofitting? Explain jacketing (conventional / RCC and steel jacketing) with neat sketches.

## Short answer

Retrofitting strengthens existing buildings to resist earthquakes without rebuilding. RCC jacketing adds 75–100 mm concrete around a column with new longitudinal bars and ties, increasing strength and ductility. Steel jacketing uses plates or angles with battens grouted to the column, providing confinement with minimal size increase.

## Answer

#### Retrofitting
**Retrofitting** is the strengthening or modification of an existing building so that it can resist earthquake forces better than it was originally designed to. It improves the strength, stiffness, ductility and load path of the existing structure without rebuilding it.

#### Jacketing
**Jacketing** is the most common retrofit method for RCC members. A new layer of material is placed around an existing column, beam or wall to increase its strength, stiffness, ductility and confinement.

#### RCC jacketing
A new concrete layer with additional steel is cast around an existing column or beam.
1. Remove loose concrete, roughen the surface and clean the bars.
2. Provide dowels (12-16 mm bars), drilled and epoxy-grouted into the footing and slab.
3. Place new longitudinal bars and closely spaced closed ties (6-8 mm at 75-100 mm c/c).
4. Apply a bonding agent and cast high-slump, small-aggregate (10-12 mm) concrete or micro-concrete; the jacket is 75-100 mm thick.
5. Cure for at least 14 days.

```text
   Before          After (RCC jacket)
  +------+       +--------------+
  |      |       | +----------+ |
  | old  |       | | old col  | |
  | col  |       | +----------+ |
  +------+       +--------------+
                  new bars + ties
```

#### Steel jacketing
Steel plates (or angles with battens/straps) are placed around the column and welded or bolted together, and the gap (about 25 mm) is filled with non-shrink cement grout. It adds confinement and shear strength with little increase in size and is quick to execute, but it needs fire and corrosion protection.

```text
   Steel plates      Angles + battens
  +==========+       L----------L
  | grout    |       | batten   |
  |  column  |       |  column  |
  +==========+       L----------L
```

**Advantages of jacketing:** increases the axial, flexural and shear capacity and the ductility of columns and beams. **Limitations:** the section size grows (RCC jacket), and workmanship at the old-new interface is critical.

## Check yourself

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

1. Jacketing is used to:
   A. Increase strength, stiffness, ductility and confinement
   B. Decorate
   C. Reduce section
   D. Remove load
   Answer: A. A new layer is added around the member. (Key point: Jacketing purpose)

2. In RCC jacketing, dowels of 12-16 mm are:
   A. Welded to roof
   B. Epoxy-grouted into footing and slab
   C. Left loose
   D. Omitted
   Answer: B. They connect jacket to footing and slab. (Key point: RCC jacket steps)

## Related in Building Technology

- [Retrofit versus repair; column jacketing](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aretrofit-vs-repair-jacketing) — Building Technology, chapter 11
- [Retrofitting a brick masonry building](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aretrofit-brick-masonry) — Building Technology, chapter 11
- [Conventional strengthening and innovative-material retrofit](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aretrofit-strengthening-innovative) — Building Technology, chapter 11
- [RCC stair for 6.0 m by 4.2 m lobby](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Arcc-stair-public-lobby-6m) — Building Technology, chapter 5
- [Vertical circulation elements; RCC dog-legged stair](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Astair-circulation-068ba) — Building Technology, chapter 5
- [Formwork for excavation, timbering, RCC formwork](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aformwork-timbering-062p) — Building Technology, chapter 8

## Related in other subjects

- [Underground RCC tank: brickwork, steel (fig a)](https://www.bctengineer.com/question.md?key=semester_7%2Festimating_and_costing%3Aug-rcc-tank-a) — Estimating and Costing, chapter 6
- [Underground RCC tank: brick, PCC, steel (1% steel)](https://www.bctengineer.com/question.md?key=semester_7%2Festimating_and_costing%3Aug-tank-b-fig1) — Estimating and Costing, chapter 6
- [Underground RCC tank: brickwork 1:4, M20 PCC, steel](https://www.bctengineer.com/question.md?key=semester_7%2Festimating_and_costing%3Aug-tank-e-fig1) — Estimating and Costing, chapter 6
- [RCC slab culvert: brick, wearing coat, GI pipe, steel](https://www.bctengineer.com/question.md?key=semester_7%2Festimating_and_costing%3Aslab-culvert-a-fig-b) — Estimating and Costing, chapter 6