Market Forms of Steel | Materials | Engineering

Following are the standard shapes in which the rolled steel sections are available in the market:

(1) Angle Sections:

The angle sections may be of equal legs or unequal legs as shown in fig. 11-3 and fig. 11-4 respectively. The equal angle sections are available in sizes varying from 20 mm x 20 mm x 3 mm to 200 mm x 200 mm x 25 mm. The corresponding weights per metre length are respectively 9 N and 736 N.

The unequal angle sections are available in sizes varying from 30 mm x 20 mm x 3 mm to 200 mm x 150 mm x 18 mm. The corresponding weights per metre length are respectively 11 N and 469 N. Fig 11-3 shows an equal angle section of size 100 mm x 100 mm x 10 mm with weight per metre length as 149 N. Fig. 11-4 shows an unequal angle section of size 90 mm x 60 mm x 10 mm with weight per metre length as 110 N.

The angle sections are extensively used in the structural steelwork especially in the construction of steel roof trusses and filler joist floors.

(2) Channel Sections:

The channel sections consist of a web with two equal flanges as shown in fig. 11-5. A channel section is designated by the height of web and width of flange. These sections are available in sizes varying from 100 mm x 45 mm to 400 mm x 100 mm. The corresponding weights per metre length are respectively 58 N and 494 N. Fig. 11-5 shows a channel section of size 300 mm x 100 mm with weight per metre length as 331 N.

The Bureau of Indian Standards has classified channel sections as junior channel, light channel and medium channel and accordingly they are designated as I.S.J.C., I.S.L.C. and I.S.M.C. respectively.

The channel sections are widely used as the structural members of the steel framed structures.

(3) Corrugated Sheets:

These are formed by passing steel sheets through grooves. These grooves bend and press steel sheets and corrugations are formed on the sheets. These corrugated sheets are usually galvanized and they are referred to as the galvanized iron sheets or G.I. sheets. These sheets are widely used for roof covering.

(4) Expanded Metal:

This form of steel is available in different shapes and sizes. Fig. 11-6 shows a plain expanded metal. It is prepared from sheets of mild steel which are machine cut and drawn out or expanded. A diamond mesh appearance is thus formed throughout the whole area of the sheet.

The expanded metal is widely used for reinforcing concrete in foundations, roads, floors, bridges, etc. It is also used as lathing material and for partitions.

(5) T-Sections:

The shape of this section is like that of letter T and it consists of flange and web as shown in fig. 11-8. It is designated by overall dimensions and thickness. These sections are available in sizes varying from 20 mm X 20 mm x 3 mm to 150 mm x 150 mm x 10 mm. The corresponding weights per metre length are 9 N and 228 N respectively.

Fig. 11-8 shows T-section of size 100 mm X 100 mm x 10 mm with weight per metre length as 150 N. The special T-sections with unequal sides, bulbs at the bottom edge of web, etc. are also available. These sections are widely used as members of the steel roof trusses and to form built-up sections.

(6) I-Sections:

These are popularly known as the rolled steel joists or beams. It consists of two flanges connected by a web as shown in fig. 11-7. It is designated by overall depth, width of flange and weight per metre length. They are available in various sizes varying from 75 mm x 50 mm at 61 N to 600 mm x 210 mm at 995 N.

Fig. 11-7 shows a joist of size 300 mm X 150 mm at 377 N. The wide flange beams are available in sizes varying from 150 mm X 100 mm at 170 N to 600 mm x 250 mm at 1451 N. The beams suitable for columns are available in H-sections which vary in sizes from 150 mm x 150 mm at 271 N to 450 mm x 250 mm at 925 N.

The Bureau of Indian Standards has classified the I-sections into junior beams, light beams, medium beams, wide-flange beams and heavy beams and they are accordingly designated as I.S.J.B., I.S.L.B., I.S.M.B., I.S.W.B. and I.S.H.B. respectively.

The R.S. joists are economical in material and they are suitable for floor beams, lintels, columns, etc. The economy in material is achieved by concentrating the material in two flanges where the bending stresses are maximum.

(7) Plates:

The plate sections of steel are available in different sizes with thickness varying from 5 mm to 50 mm. The corresponding weights per square metre are 392 N and 3925 N respectively.

They are used mainly for the following purposes in the structural steelwork:

(i) To connect steel beams for extension of the length;

(ii) To serve as tension members of steel roof truss; and

(iii) To form built-up sections of steel.

(8) Ribbed (HYSD) Bars:

These bars are produced from the ribbed which is a deformed high strength steel. These bars have ribs or projections on their surface and they are produced by controlled cold twisting of hot-rolled bars. Each bar is to be twisted individually and it is tested to confirm the standard requirements. These bars are also called High Yield Strength Deformed (HYSD) bars.

The ribbed (HYSD) bars are available in sizes varying from 6 mm to 50 mm diameter, with the corresponding weights per metre length as 2.22 N and 154.10 N.

These bars are widely used as reinforcement in concrete structures such as buildings, bridges, docks and harbour structures, roads, irrigation works, pile foundations, pre-cast concrete works, etc.

Following are the advantages of the ribbed (HYSD) bars:

(i) It is possible to bend these bars through 180° without formation of any cracks or fractures on their outside surface.

(ii) It is possible to weld certain type of ribbed HYSD bars by electric flash butt welding or arc welding.

(iii) There is overall reduction in reinforcement cost to the extent of about 30 to 40 per cent when these bars are used.

(iv) These bars are easily identified as they have got peculiar shape.

(v) These bars possess better structural properties than ordinary plain round bars. It is therefore possible to design with higher stresses.

(vi) These bars possess excellent bonding properties and hence the end hooks are not required.

(vii) They can be used for all major types of reinforced concrete structures.

(viii) They serve as efficient and economical concrete reinforcement.

(ix) When these bars are used, the processes of bending, fixing and handling are simplified to a great extent. It results into less labour charges.

(9) Round Bars:

These are available in circular cross-sections with diameters varying from 5 mm to 250 mm. They are widely used as reinforcement in concrete structures, construction of steel grillwork, etc. The commonly used cross-sections have diameters varying from 5 mm to 25 mm with the corresponding weights per metre length as 1.50 N and 38 N respectively.

(10) Square Bars:

These are available in square cross-section with sides varying from 5 mm to 250 mm. They are widely used in the construction of steel grillwork, for windows, gates, etc. The commonly use a cross-sections have sides varying from 5 mm to 25 mm with corresponding weights per metre length as 2 N and 49 N respectively.

(11) Flat Bars:

These are available in suitable widths varying from 10 mm to 400 mm with thickness varying from 3 mm to 40 mm. They are widely used in the construction of steel grillwork for windows and gates.

(12) Ribbed Mild Steel Bars:

These are the hot rolled mild steel bars but during rolling steel rods, ribs are produced on them. These ribs increase the bond strength of the bars. Such ribbed mild steel bars are not recommended in the code, but are available in the market. They look like high strength ribbed bars, but the allowable stresses in these ribbed mild steel bars are much lower than HYSD bars. These bars should not be used in R.C.C. work.

(13) Thermo-Mechanically Treated Bars (TMT Bars):

Sudden quenching of red hot steel bars by a spray of water can produce steel bars with high strength at the surface with a core of mild steel. As the core of the wire is still hot, the heat inside helps in tempering the surface. The result is a structure with tempered martensite on the periphery and a fine grained ferrite-pearlite at the centre.

The combined strength of these materials raises the yield point of steel with the high percentage of elongation at ultimate failure. TMT bars are also rolled with ribs to increase the bond strength.

They are more corrosion resistance than cold twisted bars. Special TMT-CRS bars (Thermo-Mechanically Treated Corrosion Resistant Steel bars) are also available in the market, in which high corrosion resistance is achieved by adding corrosion resistant elements like copper, phosphorous and chromium. These bars are produced in three grades like Fe 415, Fe 500 and Fe 550.

(14) Cold Twisted Deformed Bars (CTD Bars):

These were the first high strength steel bars introduced in India around I960. These bars are first hot rolled out of high grade mild steel, with three or more parallel straight ribs and other indentations on it. After cooling, they are twisted by a separate operation so that the steel is strained beyond the elastic limit and then released.

This operation raises the yield point of steel for subsequent tensile or compressive stresses. Thus, its strength is increased. Normally welding is not done in this type of steel as the strength of the steel is increased due to cold working.

CTD bars can be easily identified in the field. As the projections were rolled straight on the bars in hot rolling, they will form a helix around the bars while cold twisting. The bars can also be examined for efficiency in twisting by measuring the pitch. Cold twisting introduces residual stresses in the steel. Hence, these bars corrode much faster than other steel bars and not used in many advanced countries.

(15) Welded Wire Fabrics (WWF):

Welded wire fabric is fabricated from a series of wires arranged at right angles to each other and electrically welded at all intersections. It is made from medium tensile steel drawn out from higher diameter mild steel bars. It is much stronger than mild steel and are available in different width rolls.

Welded Wire Fabric (WWF) has various uses in reinforced concrete construction. It is mostly used for floor slabs on well-compacted ground. Heavier fabric, supplied mainly in flat sheets, is often used in walls and for the primary reinforcement in structural floor slabs. It is also used in road and runway pavements, box culverts and small canal linings.

Four numbers are used to designate the style of wire mesh i.e. 6 by 6 – 8 by 8. Here, the first number 6 indicates the lengthwise spacing of the wire in inches; the second number 6 indicates the crosswise spacing of the wire in inches; the last two numbers (8 by 8) indicate the size of the wire on the Washburn and Moen gauge.

In addition to fifteen standard shapes, the rolled steel sections are also available in miscellaneous sections such as acute and obtuse angle sections, rail sections, trough sections and z-sections. These miscellaneous sections are used to a limited extent in the structural steelwork.