---
title: "Ductile detailing of columns, confining steel"
subject: "Design of RCC Structure"
chapter: 12
key: "semester_7/design_of_rcc_structure:ductile-detailing-of-columns-confining-steel"
source: https://www.bctengineer.com/q/semester_7/design_of_rcc_structure/ductile-detailing-of-columns-confining-steel
site: BCT Engineering
---

# Ductile detailing of columns, confining steel

Design of RCC Structure · Chapter 12: Introduction to Earthquake Resistant Design and Provisions for Ductile Detailing

- Asked in: 2076 Asoj, 6 marks; 2071 Chaitra, 6 marks; 2075 Asoj, 6 marks; 2080 Bhadra, 2 marks (asked 4 times)
- Video: [Ductile Detailing of Column as per IS-13920-2016 | Column detailing IS-13920 | Column Reinforcement](https://www.youtube.com/watch?v=AZs9WOW1f94) — Civil Engineering Mastery
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_7/design_of_rcc_structure/ductile-detailing-of-columns-confining-steel
- Whole chapter: https://www.bctengineer.com/md/semester_7/design_of_rcc_structure/chapter-12

## Question

Write the provisions of ductile detailing of column / special confining reinforcement for ductile detailing of column with neat sketches.

## Short answer

Columns need min dimension 200 mm, longitudinal steel 0.8-4%, and special confining hoops over length lo = max(larger dimension, h/6, 450 mm) at each end. Hoop spacing in this zone: not less than 75 mm and not more than min(bmin/4, 100 mm); closed hoops with 135-degree hooks, 8 mm minimum diameter.

## Answer

Columns must stay stable while the beams yield, so IS 13920 asks for good confinement at the column ends, where plastic hinges can form.

#### General requirements
- Minimum dimension 200 mm (300 mm if the unsupported length exceeds 4 m or the beam span exceeds 5 m); $b/D \ge 0.4$.
- Longitudinal steel 0.8% to 4% (IS 13920; IS 456 allows up to 6%, but 4% is the practical limit for ductile columns). Lap splices only in the central half of the column height, designed as tension splices, with hoop spacing $\le 150$ mm over the lap; not more than 50% of the bars spliced at one section.

#### Special confining reinforcement
- Provided over a length $l_o$ at both ends of each column, measured from the joint face, where $l_o \ge$ the largest of: the larger lateral dimension, $h/6$ (clear height) and 450 mm.
- Hoop spacing in this zone: $s \le \tfrac14 b_{min}$, but not less than 75 mm and not more than 100 mm.
- Hoops are closed with $135^\circ$ hooks, tail $\ge 6\phi$ (not less than 65 mm). Minimum diameter 8 mm (10 mm for bars over 32 mm).
- Area of the hoop bar for a rectangular hoop:

$$
A_{sh} = 0.18\, s\, h \,\frac{f_{ck}}{f_y}\left(\frac{A_g}{A_k} - 1\right)
$$

where $A_{sh}$ is the cross-sectional area of the hoop bar, $h$ is the longer dimension of the rectangular confining hoop measured to its outer face (not more than 300 mm), $A_g$ is the gross area and $A_k$ is the area of the confined core measured to the outside of the hoops. For circular spirals, $A_{sh} = 0.09\, s\, D_k \frac{f_{ck}}{f_y}\left(\frac{A_g}{A_k}-1\right)$.
- Where a column supports a discontinued stiff member (such as a wall), the confining steel runs over the full height of the column.
- Outside $l_o$ the spacing follows IS 456 (not more than the least lateral dimension, $16\phi$ or 300 mm).

```text
   Joint ---------------
     ^     | # # # # # |  s = 75-100 mm
     | lo  | # # # # # |  (closely spaced hoops)
     v     | # # # # # |
   ------- |#  #  #  # |  
     h-2lo | #    #    |  normal spacing (IS 456)
   ------- | # # # # # |  close spacing again
```

## Check yourself

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

1. The special confining zone l_o at each column end is at least the largest of:
   A. Larger lateral dimension, h/6 and 450 mm
   B. Smaller dimension, h/3, 300 mm
   C. 2d, 8 phi, 100 mm
   D. h/2 only
   Answer: A. l_o = max(larger lateral dimension, clear height/6, 450 mm), measured from the joint face. (Key point: Confining zone length)

2. What is the hoop spacing in the special confining zone?
   A. Equal to the least lateral dimension
   B. 300 mm
   C. Not more than b_min/4 and between 75 and 100 mm
   D. 16 times bar diameter
   Answer: C. Close spacing of 75-100 mm (and <= b_min/4) confines the core where plastic hinges can form. (Key point: Hoop spacing in confining zone)

3. What end detail is required on column hoops?
   A. 90 degree hooks with 4 phi tail
   B. Open stirrups
   C. 135 degree hooks with a tail of at least 6 phi (not less than 65 mm)
   D. Straight lapped ends
   Answer: C. 135 degree hooks keep the hoop closed even after the cover spalls. (Key point: Hoop hook details)

## Related in Design of RCC Structure

- [Importance of ductile detailing, sketches](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Aimportance-of-ductile-detailing-sketches) — Design of RCC Structure, chapter 12
- [Ductile detailing of beams and columns](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Aductile-detailing-of-beams-and-columns) — Design of RCC Structure, chapter 12, asked 2×
- [Column 350x350, 1440 kN, ductile detailing](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Acolumn-350x350-1440-kn-ductile-detailing) — Design of RCC Structure, chapter 10, asked 2×
- [Short column 300x450 with ductile detailing](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Ashort-column-300x450-with-ductile-detailing) — Design of RCC Structure, chapter 10
- [Ductile design per IS 13920, beam and column](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Aductile-design-per-is-13920-beam) — Design of RCC Structure, chapter 12
- [Why ductile detailing is needed in joints](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Awhy-ductile-detailing-is-needed-in) — Design of RCC Structure, chapter 12

## Related in other subjects

- [Types of timber columns and column bases](https://www.bctengineer.com/question.md?key=semester_5%2Fdesign_of_timber_and_masonry_structures%3Atimber-column-types-and-bases) — Design of Timber and Masonry Structures, chapter 3
- [RCC column with footing: concrete and steel](https://www.bctengineer.com/question.md?key=semester_7%2Festimating_and_costing%3Arcc-column-footing-h) — Estimating and Costing, chapter 6
- [Reinforced concrete column stresses in steel and concrete](https://www.bctengineer.com/question.md?key=semester_3%2Fstrength_of_materials%3Arc-column-8-bars) — Strength of Materials, chapter 3
- [Timber columns by slenderness ratio](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Atimber-column-types-slenderness) — Design of Steel and Timber Structure, chapter 11