Determination Of The Characteristic Strength Properties Of Mild Steel Reinforcement
[A CASE STUDY OF ILORIN METROPOLIS]

These bars are furnished with surface deformations for the purpose of increasing resistance to slip between steel and concrete. Minimum requirement for these deformations (spacing, projection etc) have been developed in experimental research. Different bars producers use different pattern, all of which satisfy these requirement i.e. ASTM specification A616-6. A variety of current types of deformations are shown in the figure below.

For many years, bar sizes have been designated by numbers, Nos. 3 to 11 being two special large sized bars. The ASTM other alloying elements such as manganese, silicon, copper etc. carbon increases the hardness and strength of steel but reduces its ductility (Arthur, 2005).
25.1 GRADES AND STRENGTH
In reinforced concrete, a long term trend is evident towards the use of higher strength materials, both steel and concrete. Reinforcing bars with 40ksi yield stress have largely been replaced by bars with 60ksi yield stress because their use tends to reduce steel congestion in the forms.
Thus, Grade 40 is also designated as Grade 280 (for yield strength of 280MPa); Grade 60 is designated as 420 and 75 as Grade 520. The values 280,420 and 520 result in minimum yield strengths of 40.6, 60.9 and 75.4ksi i.e. reinforcing steel is slightly stronger than implied by the in ksi.
The two chief numerical characteristics that determine the character of bar reinforcement are its yield point (generally identical in tension and compression) and its Modulus of elasticity Es. Modulus of elasticity for all reinforcing steel is taken as Es = 29,000,000psi. Typical stress strain curve for reinforcing steels are shown below.
Low carbon steels, typified by the Grade 40 curve, show an elastic portion followed by a yield plateau i.e. a horizontal portion of the curve where strain continues to increase at constant stress. For such steels, the yield point is that stress at which the yield plateau establishes itself with further strains; the stress begins to increase again, though at a slower rate, a process that is known as stress-hardening. The curve flattens out when the tensile strength is reached. Higher strength carbon steels either have a yield plateau of much shorter length or enter strain hardening immediately without any continues yielding at constant stress.