---
title: "Development length and need of splices"
subject: "Design of RCC Structure"
chapter: 6
key: "semester_7/design_of_rcc_structure:development-length-and-need-of-splices"
source: https://www.bctengineer.com/q/semester_7/design_of_rcc_structure/development-length-and-need-of-splices
site: BCT Engineering
---

# Development length and need of splices

Design of RCC Structure · Chapter 6: Design for bond and development length

- Asked in: 2076 Asoj, 4 marks
- Video: [What is development length? | factors affecting development length | what is Ld | civil tutor | #BBS](https://www.youtube.com/watch?v=pPb2DFlW1QI) — Civil Tutor
- 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/development-length-and-need-of-splices
- Whole chapter: https://www.bctengineer.com/md/semester_7/design_of_rcc_structure/chapter-6

## Question

Define development length. Why are splices required in RCC structure?

## Short answer

Development length L_d = 0.87 f_y φ/(4 τ_bd) prevents pull-out. Splices are required because bars come in limited lengths, for transport, connecting construction stages, ensuring load path continuity, and using short offcuts; lap, welded and mechanical coupler splices are used.

## Answer

#### Development length

Development length $L_d$ is the length of embedded bar needed to develop its design stress $0.87f_y$ by bond with the concrete:

$$
L_d=\frac{0.87f_y\,\phi}{4\,\tau_{bd}}
$$

For example, for Fe415 deformed bars in M20 concrete, $\tau_{bd}=1.2\times1.6=1.92$ N/mm$^2$ and $L_d=47\phi$.

#### Why splices are required

Reinforcing bars are available only in standard lengths (usually 12 m, and often shorter in practice because of transport). Splices (joints) are therefore needed for the following reasons:

1. **Limited length of bars:** members longer than the available bar length, such as long beams, tall columns and walls, need bars to be joined.
2. **Transport and handling:** long bars are difficult to carry, store and fix on site.
3. **Construction stages:** column bars are left projecting above each floor and lapped with the bars of the next lift (at construction joints).
4. **Continuity of load path:** splices transfer the full force from one bar to the next, so the reinforcement acts as a continuous bar.
5. **Economy:** short offcuts of bars can be used instead of being wasted.

**Types:** lap splices (most common), welded joints and mechanical couplers. Laps should be staggered, be at least $L_d$ or $30\phi$ (flexural tension), and should not be placed at sections of maximum stress.

## Check yourself

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

1. Ld for Fe415 deformed bar in M20 equals about 47φ because
   A. τbd = 1.2 N/mm² for deformed bars
   B. fy is replaced by fck
   C. deformed bars reduce τbd by 60%
   D. τbd = 1.2 × 1.6 = 1.92 N/mm² for deformed bars
   Answer: D. Deformed bars have a 60% higher bond stress, giving Ld = 0.87×415φ/(4×1.92) = 47φ. (Key point: Ld meaning)

2. Why are splices needed in RCC?
   A. Bars are too heavy to be placed
   B. Bars are supplied in limited standard lengths and structures are built in stages
   C. To lower steel grade
   D. To reduce concrete cover
   Answer: B. Standard bar lengths (about 12 m) and construction stages require joining bars. (Key point: Need of splices)

3. What must a splice achieve?
   A. Reduce the load on the beam
   B. Make bars shorter
   C. Prevent any lapping
   D. Transfer the full force from one bar to the next so steel acts as continuous
   Answer: D. Splices maintain continuity of the load path. (Key point: Splice function)

4. Which is a correct rule for laps?
   A. Less than Ld to save steel
   B. All at maximum stress sections
   C. Never staggered
   D. Staggered, at least Ld or 30φ, not at sections of maximum stress
   Answer: D. Laps must be staggered, adequate in length and away from maximum stress. (Key point: Splice rules)

## Related in Design of RCC Structure

- [Derive development length expression](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Aderive-development-length-expression) — Design of RCC Structure, chapter 6, asked 6×
- [Bond and development length with derivation](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Abond-and-development-length-with-derivation) — Design of RCC Structure, chapter 6, asked 3×
- [Define development length and lap splice](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Adefine-development-length-and-lap-splice) — Design of RCC Structure, chapter 6
- [Define development length (short)](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Adefine-development-length-short) — Design of RCC Structure, chapter 6
- [Types of mechanical splices](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Atypes-of-mechanical-splices) — Design of RCC Structure, chapter 7
- [Two-way slab on RCC beams, 4x6 m](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Atwo-way-slab-on-rcc-beams) — Design of RCC Structure, chapter 9, asked 2×

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