Brief Information on Rebars

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BENEFITS OF USE OF HIGH (YIELD) STRENGTH DEFORMED BARS IN R.C.C. STRUCTURES

1. Following materials are used in the R.C.C. structures:-

(1) Cement(2) Steel(3) Sand(4) Aggregates(5) Water

2. Different types of steel bars used in R.C.C. works are mentioned below: 1) Mild Steel plain bars (Generally M.S. round bars are used) 2) Medium Tensile Steel bars
3) High yield strength deformed bars (H.Y.S.D. bars) 1. Mild Steel Bars (M.S. Bars)
In past, mild steel was available in two different categories. 1. M.S. Plain Bars:-

M.S. plain bars of round section confirm to I S 432 – Part – I, 1982 (Grade-I) and (Grade-II) is most commonly used and easily available in the market. It’s diameter denoted by Ø. The permissible tensile strength of the mild steel confirm to grade-I of I S 432 – Part-I, 1982 is a) 140 N/mm² for bars up to and including 20 mm Ø b) 130 N/mm² for bars over 20 mm Ø

The permissible tensile strength for mild steel confirming to grade-II of I S 432 – Part-I, 1982 is @ 90 % of grade-I bars. Hence if the design details have already been worked out on the basis of Mild Steel confirming to grade-I of I S 432 – Part-I, 1982 and it happens to use grade-II of Mild Steel than the area of reinforcement shall be increased by 10 % of the required for grade-I steel. More over I S 432 – Part-I, 1982 does not recommend the grade-II M.S. bars for use in structures located in earthquake zone subjected to severely damage and structures subjected to dynamic loading (other than wind loading)

2. M.S. Deformed Bar (or Deformed Mild Steel Bars):- In past deformed M.S. bars were also available in the market confirm to I S 1139 – 1966. Deformed bars are furnished with lugs, ribs or other surface deformation. The technical specification of such deformed bars are mentioned below: (a) Permissible tensile stress : -140 N/mm² for bars up to and including 20 mm Ø 130 N/mm² for bars over 20 mm Ø` (b) Yield stress : -260 N/mm² for bars up to and including 20 mm Ø 240 N/mm² for bars over 20 mm Ø (c) Ultimate tensile stress : -420 N/mm² for all size diameter of bars Since the basic materials for plain mild steel bars and deformed mild steel bars is the same, hence the specifications for deformed mild steel bars has to be as far as possible in line with the specification for plain mild steel bars. The above-mentioned M.S. deformed bars were known as Fe 250 bars in the market, where figure followed the symbol Fe indicates the yield stress in N/mm². But, after publishing I S 1786 – 1985 which supercedes I S 1139 – 1966 and as per the clause 0.3 of I S 1786 – 1985. Fe 250 strength grade has been deleted. Therefore material of Fe 250 grade i.e. deformed M.S. bars should not be used for Government Works. 2. Medium Tensile Steel:-

This type of material is not commonly used in general R.C.C. work. Hence only elementary information are collected and mentioned here. 2.2.1(I)Medium Tensile Plain Bars (of round section)

It should confirm I S 432 – Part-I, 1982
(a) Permissible tensile stress :-Half the guaranteed yield stress to maximum of 190 N/mm² 2.2.2Medium Tensile Deformed Bars:-
In past, deformed medium tensile steel bars were also available in the market confirm to I S 1139 – 1966. The technical specifications of such deformed bars are mentioned below: (a) Permissible tensile stress : -Half the guaranteed yield stress to maximum of 190 N/mm² (b) Yield stress : -360 N/mm² for bars up to and including 16 mm Ø...
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