Steeel

civil engineering s2 ktu syllabus

1. STEEL Steel: uses of steel in building construction types –market forms

2. STEEL Metals are widely used in construction field. Out of the various metals iron is the most popular one Based on the carbon content in iron, it can be classified into 3 as Based on the carbon content in steel, it can be classified into 3 as Carbon Content in Iron Wrought iron Does not exceed 0.15% Steel Below 0.25% to 1.50% maxi Cast-iron (pig iron) 2 to 4% Name of steel Carbon Content in Steel Very low carbon steel(dead steel) < 0.1% Mild steel Up to 0.25 % Medium carbon Steel 0.25 – 0.7 % High carbon Steel (hard steel) 0.7 – 1.5%

3. NOTE 1 Dividing line of cast-iron & steel is the presence of free graphite If carbon content > 1.5%, it does not combine with iron & it is present as free graphite If there is no free graphite in the composition of a material, it is said to be steel On the other hand, the presence of free graphite indicate that the material is cast-iron NOTE 2 If a drop of nitric acid is placed on steel, it will produce a dark grey strain due to the presence of higher carbon content If the same procedure is carried out on wrought-iron , the strain will not be appreciable Thus a mild steel & wrought iron can be easily distinguished

4. Uses of Steel Cast iron is granular and can take up only compressive stress and hence it is use is compressive members. Wrought iron is fibrous in nature and it is suitable to resist tensile stresses. Steel is strong in compression and tension hence it is suitable for all construction works Steels are highly elastic, ductile , malleable and weldable They can be hardened and tempered and are fusible at a low temperature than wrought iron They retain magnetic properties as iron Fractured Wrought Iron Fractured Cast Iron

5. Types of Steel Properties Uses Mild Steel Soft and malleable steel is used for rolling into thin sheets For making motor body, sheet metal, boiler plates, tin plates, structural steel etc Medium Carbon Steel Very soft and ductile steel used for drawing into wires For making springs, tyres , stamping and pressing dies, rails High Carbon Steel Very hard and brittle steel used for making tools For making chisels, hammers, saw, smithy tools, stone mason’s tool, axes, drills, knives

6. Properties of mild steel & hard steel Mild Steel Hard Steel Tougher & elastic than wrought iron Tougher & elastic than mild steel Can be readily forged & welded Cannot be readily forged & welded Cannot be easily hardened & tempered Can be easily hardened & tempered It has fibrous structure It has granular structure Melting point 1400  C Melting point 1300  C Specific gravity 7.80 Specific gravity 7.90 Can be magnetised permanently Not easily attacked by salt water It rusts easily and rapidly

7. Market forms of steel Following are the standard shapes in which the steel sections are available in the market: (1) Angle sections (2) Channel sections (3) I- sections (4) T- sections (5) Round bars (6) Square bars (7) Corrugated sheets (8) Expanded metal (9) Flat bars (10) Plates (11) Ribbed tor steel bars

8. 1. Angle sections : Angle sections have two legs If two legs are of equal length then they are known as equal angle section and otherwise called as unequal angle section 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 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 . Extensively used in the structural steelwork especially in the construction of steel roof trusses and filler joist floors 100 mm x 100 mm x 10 mm (weight 149 N/m) 90 mm x 60 mm x 10 mm (weight 110 N/m)

9. b x a x c Angle Sections

10. 2. Channel Sections: The channel sections consist of a web with equal flanges 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 Bureau of Indian Standards has classified channel sections as ISJC - Indian Standard Junior Channel ISLC - Indian Standard Light Channel ISMC - Indian Standard Medium Channel ISSC - Indian Standard Special Channel The channel sections are widely used as the structural members in steel - framed structures, crane girders, beams & steel bridges 300 mm x 100 mm (weight 331 N/m)

11. Channel Sections

12. 3. I-Sections Commonly known as Rolled Steel Joist (RSJ) or beams . An I section consist of two flanges and a connecting web It is designated by overall depth width of flange and weigth per meter length. They are available in various sizes from 75mm x 50mmx at 61 N/m to 600mm x 210mm at 995N/m. 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 .

13. RSJ are economical in material and are suitable for beams, lintels, columns, grillage foundations etc. Unequal I sections with heavy weight are used as rails

14. I-Sections

15. 4. T-sections The shape of the section is like that of letter T it consists of flange and web 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. These sections are widely used as members of the steel roof trusses and to form built-up sections.

16. 5. Round Bars These are available in circular cross-sections with diameters varying from 5 mm to 25 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 as 1.50 N/m and 38 N/m respectively.

17. 6. Square Bars These are available in square cross-section with sides varying from 5 mm to 25 mm. They are widely used in the construction of steel grillwork, for windows, gates, etc. Commonly used cross-sections have sides varying from 5 mm to 25 mm with corresponding weights per meter length as 2 N and 49N.

18. 7. 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.

19. 8. Expanded Metals Formed by cutting and expanding either plain sheets or ribbed sheets of mild steel. A diamond mesh appearance is formed through out the area The manufactures sheets are thus known as diamond mesh or rib mesh. Diamond mesh has sizes from 30 to 150mm across the shorter length of the mesh and is available in length 1 to 3m and width 5m Expanded metal is used as roads, floors, bridges, reinforcing concrete foundations etc. It is also used as lathing material and for partitions

20. Expanded Metals

21. 9. Flat bars These are available in widths varying from 10 mm to 400 mm thickness varying from 5mm to 40 mm They are widely used in the construction of steel grillwork for windows and gates.

22. 10 Plates The plate sections of steel are available in different sizes with thickness varying from 5 mm to 50 mm. 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 tensional members of steel roof truss and (iii) to form built-up sections of steel

23. Plates

24. Types reinforcing bars The steel bars used in reinforced cement concrete are called reinforcing bars or rebars . These are of two types. Plane steel bars: Tor steel bars: Plane steel bars: Round sections, which are made up of mild steel, medium tensile steel or high tensile steel are used in reinforced cement concrete. But the present trend in India is to go for tor steel bars. Plane steel bars are available from 5mm to 32 mm for reinforcing purpose.

25. Ribbed-tor steel bars These bars are produced from the ribbed-tor steel 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. The ribbed-tor steel bars are available in sizes varying from 6 mm 50mm diameter, with the corresponding weights as 2.22 N/m and 154.10 N/m.

26. Ribbed-tor steel bars

27. These bars are widely used as reinforcement a concrete structures such as buildings, bridges, docks and harbor structure, roads, irrigation works, pile foundations, pre-cast concrete works, etc. Following are the advantages of the ribbed-tor steel bars It is possible to bend these bars through 180  without formation of any cracks or fractures on their outside surface. It is possible to weld certain type of ribbed-tor steel bars by electric flash, butt welding or arc welding. There is overall reduction in reinforcement cost to the extent of about 30 to 40% when these bars are used. These bars are easily identified as they have got peculiar shape.

28. These bars possess better structural properties than ordinary plain round bars. It is therefore possible to design with higher stresses. These bars possess excellent bonding properties and hence the end hooks are not required. They can be used for all major types of reinforced concrete structures. They serve as efficient and economical concrete reinforcement. When these bars are used, the processes of bending, fixing and handling are simplified to a great extent. It results into less labour charges.

29. Type of steel Yield stress Mild steel (Plain bars) 250 Mpa High Yield Strength Steel 415 Mpa (Cold twisted 500 Mpa deformed bars)