Properties of reinforcing steel
Steel reinforcement used in reinforced concrete may be of the following types
(a) 1. Mild steel bars conforming to IS 432 (part-I)
2. Hot rolled mild steel conforming to IS 1139
(b) 1. Medium tensile steel conforming to IS 432 (part-I)
2. Hot rolled medium tensile steel.
(c) 1. Hot rolled High Yield Strength Deformed (HYSD) steel conforming to IS 1139.
2. Cold-worked steel HYSD bars steel conforming to IS 1786.
(d) 1. Hard drawn steel wire fabric conforming to IS 1566.
2. Rolled steel made from structural steel conforming to Is 226.
1. the most important characteristic of a reinforcing bar is its stress strain curve and the important property yield stress or 0.2% proof stress, as the case may be. The modules of elasticity E for these steel is 2×105 N/mn2.
2. Mild steel bars have yield strength of 250 N/mm2 and hence it is known as Fe 250.
3. HYSD bars may be hot rolled high yield strength bars or cold rooked steel high strength deformed bars. The latter are also known as cold twisted deformed bars or Tor steel and are available in different grades
i) Fe 415 ii) 500 iii) Fe 550 having 0.2% proof stress as 415N/mm2, 500N/mm2 and 550 N/mm2
5. The reinforcing bars should have sufficient % of elongation.
6. Its coefficients of thermal expansion should be more or less equal to the cement concrete.
Stress-strain curves for reinforcement
Figures 1.2 and 1.3 show the representative stress-strain curves for steel having definite yield
point and not having definite yield point, respectively. The characteristic yield strength fy
of steel is assumed as the minimum yield stress or 0.2 per cent of proof stress for steel having no
definite yield point. The modulus of elasticity of steel is taken to be 200000 N/mm2
For mild steel, the stress is proportional to the strain up to the yield point. Thereafter, post
yield strain increases faster while the stress is assumed to remain at constant value of fy.
For cold-worked bars (Fig. 1.3), the stress is proportional to the strain up to a stress of 0.8 fy. Thereafter, the inelastic curve is defined as given below:
Linear interpolation is to be done for intermediate values. The two grades of cold-worked bars used as steel reinforcement are Fe 415 and Fe 500 with the values of fy as 415 N/mm2 and 500 N/mm2, respectively.