Building Materials, Third Edition

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A channel section is designated by its depth and weight. For instance, I.S.L.C, 350 @ 380.6
N/m means that the channel section is 350 mm deep and the self weight is 380.6 N per metre
length.

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A T-section is designated by its depth and weight, e.g., I.S.N.T. 125 @ 268.8 N/m, means the
Tee section is 125 mm deep and the self weight is 268.8 N per metre length.
An angle-section is designated by its leg lengths and thickness. For example, I.S.A.
40 × 25 × 6 mm means, the section is an unequal angle with legs 40 mm and 25 mm in length
and thickness of the legs 6 mm.
Steel tubes are designated by their outside diameter and self weight.
Steel flats are designated by width and thickness of the section, e.g., 30 I.S.F. 10 mm means
the flat is 30 mm wide and 10 mm thick.
Steel plates are designated by length, width and thickness, e.g., I.S.P.L.
2000 mm × 1000 mm × 8 mm, means the plate is 2000 mm long, 1000 mm wide and 8 mm thick.
Steel sheets are designated by length, width and thickness, e.g., I.S.SH.
2000 mm × 600 mm × 4 mm, means the sheet is 2000 mm long 600 mm wide and 4 mm thick.
Steel strips are designated by width and thickness, e.g., I.S.ST. 200 mm × 2 mm, means the
strip is 200 mm wide and 2 mm thick.
The round bars are generally used as reinforcement in reinforced and forestressed concrete
structures, and are dealt in details in the section to follow. These as well as square bars are used
also for decorative purposes and grills for fencing, parapets etc.

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Cement concrete is one of the most versatile and established construction material throughout
the world. Concrete being extremely weak in tension requires reinforcement, which is in
variably steel. Steel reinforcement is available in the form of bars of specific diameters with
different chemical composition, e.g., mild steel and high tensile steel, and surface characteristics—
plain or deformed. The types and grades of reinforcing bars are given in Table 13.2. Good steel
should not have carbon content of more than 0.25%, sulphur content of more than 0.05% and
phosphorus content of more than 0.05%.
Effectiveness of concrete reinforcement may be enhanced by the use of low-alloy steel, or by
mechanical strengthening, or by heat treatment. Mechanical strengthening of steel is done by
drawing, stretching, twisting; the yield point of steel rises by about 30%. Heat treatment
increases strength and improves mechanical properties of steel and effects 30 to 40% savings on
reinforcement.
Steel bars can also be strengthened by cold drawing after rolling. Mild steel has a definite
yield point. Cold working increases the yield stress of mild steel. Higher yield strength of
reinforcing steel bars lowers the steel requirement and thus the cost of reinforcement and its
fixing is reduced. The major drawback of cold working is the introduction of internal stresses
in steel bars. Some of the other disadvantages of cold working are reduced ductility of steel,
and reduced shear strength of RCC beams; the longitudinal tensile reinforcement is reduced.
Heating of cold worked steel to high temperatures results in annealing of steel causing loss of
increased strength due to cold working.