---
title: "Characteristics of reinforcing steel bars"
subject: "Design of RCC Structure"
chapter: 3
key: "semester_7/design_of_rcc_structure:characteristics-of-reinforcing-steel-bars"
source: https://www.bctengineer.com/q/semester_7/design_of_rcc_structure/characteristics-of-reinforcing-steel-bars
site: BCT Engineering
---

# Characteristics of reinforcing steel bars

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

- Asked in: 2065 Kartik (old course), 5 marks
- Video: [Properties of Rebar for Reinforced Concrete Design](https://www.youtube.com/watch?v=7DovGzBOB_I) — Tyler Ley
- 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/characteristics-of-reinforcing-steel-bars
- Whole chapter: https://www.bctengineer.com/md/semester_7/design_of_rcc_structure/chapter-3

## Question

Write the characteristics of steel reinforcing bars used in reinforced concrete structures.

## Short answer

Reinforcing steel characteristics: high tensile strength (Fe250, Fe415, Fe500, Fe550), ductility (12-23% elongation), Es=2×10^5 N/mm², yield behavior (definite yield for mild steel, 0.2% proof stress for HYSD), good bond via ribs, thermal compatibility (α≈1.2×10^-5/°C), weldability/bendability, fu/fy≥1.10, corrosion resistance (TMT), density 7850 kg/m³, sizes 6-32mm.

## Answer

Reinforcing steel is used in RCC to carry tension (and compression) and to control cracking. IS 1786 covers HYSD/TMT bars and IS 432 covers mild steel bars.

**Main characteristics**

1. **High tensile strength:** Fe250 ($f_y=250$), Fe415 ($f_y=415$), Fe500 ($f_y=500$) and Fe550 ($f_y=550$ N/mm$^2$).
2. **Ductility:** elongation of at least 23% (Fe250), 14.5% (Fe415) and 12% (Fe500); ductile steel gives warning before failure. Fe500D and Fe550D give higher ductility for seismic use.
3. **Modulus of elasticity:** $E_s=2\times10^5$ N/mm$^2$ for all grades.
4. **Yield behaviour:** mild steel has a definite yield point; HYSD/TMT bars have no sharp yield point, so the 0.2% proof stress is taken.
5. **Good bond:** ribs/deformations on the surface give better bond with concrete (the design bond stress is increased by 60% for deformed bars).
6. **Thermal compatibility:** the coefficient of expansion is about $1.2\times10^{-5}$ per $^\circ$C, nearly equal to that of concrete, so no significant internal stress develops with temperature change.
7. **Weldability and bendability:** bars should bend without cracking (bend and rebend tests); the carbon equivalent is limited for weldability.
8. **Ultimate to yield ratio:** $f_u/f_y\ge1.10$ (1.08 for Fe500) to ensure reserve strength.
9. **Corrosion resistance:** TMT bars have a tough outer surface and a softer core, giving better corrosion resistance than cold-twisted bars.
10. **Density:** 7850 kg/m$^3$; bars are available in sizes 6, 8, 10, 12, 16, 20, 25 and 32 mm.

## Check yourself

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

1. How does HYSD/TMT bar yield behaviour differ from mild steel?
   A. It has a sharper yield point
   B. It has no sharp yield point so the 0.2% proof stress is used
   C. It has no elasticity
   D. Its modulus is lower
   Answer: B. Mild steel has a definite yield; HYSD bars use the 0.2% proof stress. (Key point: Yield behaviour)

2. Why is the thermal property of steel suitable for RCC?
   A. Its expansion coefficient (about 1.2 x 10^-5 per °C) is nearly equal to concrete's
   B. It does not expand at all
   C. It expands much more than concrete
   D. It conducts no heat
   Answer: A. Nearly equal expansion means no internal stress arises from temperature change. (Key point: Thermal compatibility)

3. Why is ductility an important steel characteristic?
   A. It gives warning through large deformation before failure
   B. It increases the weight
   C. It reduces bond
   D. It raises modulus
   Answer: A. Ductile steel deforms visibly before it fails. (Key point: Ductility)

4. What is the modulus of elasticity of reinforcing steel?
   A. 2 x 10^5 N/mm^2 for all grades
   B. 2 x 10^4 N/mm^2
   C. 5000 sqrt(fck)
   D. Depends on grade (higher for Fe500)
   Answer: A. Es = 2 x 10^5 N/mm^2 regardless of grade. (Key point: Modulus)

## Related in Design of RCC Structure

- [Steel requirement and doubly reinforced moment](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Asteel-requirement-and-doubly-reinforced-moment) — Design of RCC Structure, chapter 2
- [Check column 600x400 with 8-28 mm bars](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Acheck-column-600x400-with-8-28) — Design of RCC Structure, chapter 10
- [Bent-up bars, 600 mm effective depth](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Abent-up-bars-600-mm-effective) — Design of RCC Structure, chapter 5, asked 2×
- [Ultimate moment of L-beam, doubly reinforced](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Aultimate-moment-of-l-beam-doubly) — Design of RCC Structure, chapter 4
- [Moment of resistance of doubly reinforced beam](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Amoment-of-resistance-of-doubly-reinforced) — Design of RCC Structure, chapter 4
- [Footing 350x350, 8-16 mm bars, reversible moment](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Afooting-350x350-8-16-mm-bars) — Design of RCC Structure, chapter 11

## Related in other subjects

- [Rationale for reinforcing concrete with steel](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Arationale-steel-reinforcement) — Concrete Technology and Masonry Structure, chapter 1
- [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
- [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
- [Fibre-reinforced plastics: characteristics, applications](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Afrp-characteristics) — Engineering Chemistry, chapter 4