---
title: "Characteristic and design strength and loads"
subject: "Design of Steel and Timber Structure"
chapter: 3
key: "semester_6/design_of_steel_and_timber_structure:characteristic-strength-loads"
source: https://www.bctengineer.com/q/semester_6/design_of_steel_and_timber_structure/characteristic-strength-loads
site: BCT Engineering
---

# Characteristic and design strength and loads

Design of Steel and Timber Structure · Chapter 3: Limit State Design Method

- Asked in: 2081 Chaitra, 1+1+1+1 marks
- Video: [Characteristics Strength, Design Strength, Characteristics Load and Design Load| Lecture 16](https://www.youtube.com/watch?v=8Z7jbtTBgH8) — Tech Master Academy
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/design_of_steel_and_timber_structure/characteristic-strength-loads
- Whole chapter: https://www.bctengineer.com/md/semester_6/design_of_steel_and_timber_structure/chapter-3

## Question

Discuss about characteristic strength, characteristic loads, design strength and design loads.

## Short answer

Characteristic strength is the minimum material strength with a 5% exclusion limit. Characteristic load is the load with a 5% probability of being exceeded in the structure's life. Design strength equals characteristic strength divided by partial safety factor for material; design load equals characteristic load multiplied by load factor.

## Answer

- **Characteristic strength:** the value of material strength (e.g. yield stress $f_y$ or ultimate $f_u$) below which not more than 5% of test results are expected to fall. It is the specified minimum strength in IS 2062.
- **Characteristic load:** the value of load (dead, live, wind, seismic) which has an accepted probability (about 5%) of being exceeded during the life of the structure. It is taken from IS 875 / IS 1893 / NBC.
- **Design strength:** characteristic strength divided by the partial safety factor for material, $f_d=f_k/\gamma_m$ (e.g. $f_y/1.10$, $f_u/1.25$).
- **Design load:** the characteristic load multiplied by the partial safety factor for load, $F_d=\gamma_f F_k$ (e.g. $1.5\times$ DL+LL). Design loads are also called factored loads.

## Check yourself

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

1. How is characteristic strength defined?
   A. Value below which not more than 5% of test results are expected to fall
   B. Average of test results
   C. Value exceeded by 5% of loads
   D. Strength divided by gamma_m
   Answer: A. It is the strength value below which not more than 5% of results fall, e.g. specified minimum in IS 2062. (Key point: Characteristic strength)

2. What is a characteristic load?
   A. Load multiplied by gamma_f
   B. Average load
   C. Load with about 5% probability of being exceeded during structure life
   D. Minimum possible load
   Answer: C. Characteristic load has an accepted probability (about 5%) of being exceeded. (Key point: Characteristic load)

3. Design strength is obtained by:
   A. Multiplying characteristic strength by gamma_m
   B. Dividing characteristic strength by gamma_m
   C. Dividing load by gamma_f
   D. Adding gamma_m to fy
   Answer: B. f_d = f_k / gamma_m, e.g. fy/1.10 or fu/1.25. (Key point: Design strength)

## Related in Design of Steel and Timber Structure

- [Design strength of ISA 100x75x6, 6 bolts](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Aangle-design-strength-100x75x6) — Design of Steel and Timber Structure, chapter 5, asked 2×
- [Deodar beam with two point loads, 4 m](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Atimber-beam-deodar-two-point-loads) — Design of Steel and Timber Structure, chapter 12
- [Strength of double cover butt joint, M20](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Adouble-cover-butt-joint-strength) — Design of Steel and Timber Structure, chapter 4
- [Tensile strength of ISA 100x75x8, six M20 bolts](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Aangle-strength-isa100x75x8-m20) — Design of Steel and Timber Structure, chapter 5
- [Ultimate strength of ISA 100x100x10, M20 bolts](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Aangle-ultimate-strength-100x100x10) — Design of Steel and Timber Structure, chapter 5
- [Tensile strength of ISA 100x75x8, M16 8.8](https://www.bctengineer.com/question.md?key=semester_6%2Fdesign_of_steel_and_timber_structure%3Aangle-design-strength-100x75x8-m16-88) — Design of Steel and Timber Structure, chapter 5

## Related in other subjects

- [Characteristic strength and characteristic load](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Acharacteristic-strength-and-characteristic-load) — Design of RCC Structure, chapter 1, asked 3×
- [Idealized stress-strain, characteristic strength](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Aidealized-stress-strain-characteristic-strength) — Design of RCC Structure, chapter 3
- [Characteristic strength at 95% confidence](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Acharacteristic-strength-16-17) — Concrete Technology and Masonry Structure, chapter 5
- [Characteristic strength of concrete cubes](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Acharacteristic-strength-cubes-26) — Concrete Technology and Masonry Structure, chapter 5