---
title: "Limit state of serviceability, requirements"
subject: "Design of RCC Structure"
chapter: 3
key: "semester_7/design_of_rcc_structure:limit-state-of-serviceability-requirements"
source: https://www.bctengineer.com/q/semester_7/design_of_rcc_structure/limit-state-of-serviceability-requirements
site: BCT Engineering
---

# Limit state of serviceability, requirements

Design of RCC Structure · Chapter 3: Limit State Method of design

- Asked in: 2075 Chaitra, 4 marks; 2068 Baisakh (old course), 5 marks (asked 2 times)
- Video: [Limit State of Serviceability and Its Types -  Theory of Reinforced Concrete Structures](https://www.youtube.com/watch?v=wvzTDxtwMMA) — Ekeeda
- 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/limit-state-of-serviceability-requirements
- Whole chapter: https://www.bctengineer.com/md/semester_7/design_of_rcc_structure/chapter-3

## Question

Explain/discuss the limit state of serviceability and its requirements in the limit state design of RC structures.

## Short answer

Serviceability limit state is when structure becomes unfit for use despite being safe against collapse; checked at service loads with γm=1.0. Requirements: deflection ≤ span/250 total and ≤ span/350 or 20mm after finishes; crack width ≤ 0.3mm (0.2mm aggressive); durability via cover, cement content, w/c ratio; vibration and fire resistance where relevant.

## Answer

The **limit state of serviceability** is the state beyond which the structure, though safe against collapse, becomes unfit for normal use because of excessive deflection, cracking, vibration or other defects. It is checked at **service (unfactored) loads** with a material partial factor $\gamma_m=1.0$.

#### Requirements (IS 456:2000, cl. 35.3, 23.2 and 26.3)

1. **Deflection**
   - Final deflection (including the effects of creep, shrinkage and temperature) $\le$ span/250.
   - Deflection after construction of partitions and finishes $\le$ span/350 or 20 mm, whichever is less.
   - Satisfied by the span/effective depth ratio: basic values 20 (simply supported), 26 (continuous) and 7 (cantilever), modified for steel stress and compression steel.
2. **Cracking**
   - Crack width generally limited to 0.3 mm (0.2 mm where members are exposed to weather, moisture or aggressive conditions).
   - Satisfied by minimum steel and by limiting the bar spacing (cl. 26.3.3): in beams, the clear distance between tension bars should not exceed the values of Table 15 (e.g. 280, 180 and 150 mm for Fe250, Fe415 and Fe500 with no redistribution); in slabs, main bars are spaced at not more than $3d$ or 300 mm.
3. **Durability**
   - Adequate nominal cover, minimum cement content, maximum water-cement ratio and minimum grade according to the exposure (mild to extreme).
4. **Vibration**
   - Slender members should not vibrate noticeably; limit the span/depth ratios.
5. **Fire resistance**: cover and member dimensions as per IS 456 Table 16A and Fig. 1.

These checks protect the appearance, comfort and long-term life of the structure.

## Check yourself

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

1. How is the limit state of serviceability defined?
   A. State beyond which the structure collapses
   B. State beyond which the structure, though safe, is unfit for normal use due to deflection, cracking, etc.
   C. State where steel yields
   D. State where concrete reaches 0.0035 strain
   Answer: B. Serviceability concerns usability and appearance, not collapse. (Key point: Definition)

2. What crack width limit is generally specified?
   A. 0.1 mm always
   B. 0.3 mm (0.2 mm in severe exposure)
   C. 1 mm
   D. 0.5 mm in severe exposure
   Answer: B. Crack widths are limited to 0.3 mm, and to 0.2 mm in severe exposure, to protect steel and appearance. (Key point: Crack width)

3. How is the deflection requirement usually satisfied in design?
   A. Computing the deflection by double integration only
   B. Limiting the span/effective depth ratio (basic 20 simply supported, 26 continuous, 7 cantilever)
   C. Using more stirrups
   D. Increasing steel to 4%
   Answer: B. The code allows deflection control by span/depth ratios modified for steel stress and compression steel. (Key point: Meeting deflection)

## Related in Design of RCC Structure

- [Limit states of strength and serviceability](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Alimit-states-of-strength-and-serviceability) — Design of RCC Structure, chapter 3, asked 3×
- [Serviceability limit state and splicing types](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Aserviceability-limit-state-and-splicing-types) — Design of RCC Structure, chapter 3
- [Ductility requirements of RC beam with sketch](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Aductility-requirements-of-rc-beam-with) — Design of RCC Structure, chapter 12, asked 4×
- [Serviceability; short and long-term deflection](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Aserviceability-short-and-long-term-deflection) — Design of RCC Structure, chapter 8
- [Limit state design of beam, 45 kN/m](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Alimit-state-design-of-beam-45) — Design of RCC Structure, chapter 4
- [Types of design methods for RC](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Atypes-of-design-methods-for-rc) — Design of RCC Structure, chapter 1

## Related in other subjects

- [Safety and serviceability requirements](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Asafety-serviceability-requirements) — Design of Steel and Timber Structure, chapter 3, asked 2×
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- [Different limit states in steel design](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Atypes-of-limit-states) — Design of Steel and Timber Structure, chapter 3
- [Design philosophies for steel structures](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Adesign-philosophies-steel) — Design of Steel and Timber Structure, chapter 1