1. Dr S.Sreenath Phd, MSc Engg, MSc (ICM), MBA
Steel Construction
Dr S.Sreenath Phd, MSc Engg, MSc (ICM), MBA

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6. Steel Construction - Introduction
Steel is the preferred choice for Quality, Buildability, Productivity and Cost Effectiveness.
The design of steel structures involves planning of the structure for specific purposes, proportioning of members to carry loads in the most economic manner.
The structure should serve the purpose for which it is intended.
It should have adequate strength to withstand direct and induced forces to which it may be subjected during its life span.
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7. Advantages of steel High strength per unit weight.
Can be conveniently handled and transported.
Properly maintained steel structures have a long life.
The properties of steel mostly do not change with time.
Steel being a ductile material does not fail suddenly, but gives visible evidence of impending failure by large deflections.
They can erect faster.
Steel has the highest scrap value.
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8. Disadvantage of steel
In exposed conditions are subjected to corrosion.
Require fire proof treatment, which increases cost.
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9. Effects of elements present in steel
Carbon – controls the hardness and stiffness of steel.
Silicon – tendency to cause brittleness and its presence is limited to a maximum of 0.3%.
Phosphorus – renders steel brittle at ordinary temperatures and its presence is limited to a maximum allowance percentage is normally 0.055%.
Sulphur – it makes steel brittle and likely to crack when heated to red hot stage. The percentage of sulphur is therefore limited to 0.055%.
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10. Effects of elements present in steel
Manganese – beneficial to steel and ranges from 1.1% to 1.65%.
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11. Mild Steel Composition Carbon 0.23-0.25% Sulphur 0.055%
Phosphorus 0.055%
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12. Properties of Mild Steel
Its structure is fibrous with dark bluish colour.
It is malleable and ductile.
It is more tough and elastic than cast iron and wrought iron.
It can easily be welded, riveted and forged.
It is equally strong in compression, tension and in shear.
It is difficult to harden and temper.
Its specific gravity is 7.8.
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13. Uses Mild Steel
As rolled sections like I – section, T – section, channel section, angle iron, plates, round and square rods in construction works.
Extensively used as reinforcements in Reinforced Cement Concrete (RCC).
Mild steel tubes are finding much use in structures.
Plain and corrugated sheets of mild steel are being used as roof coverings.
Mild steel is also used in the manufacture of various tools and equipments, machine parts, towers and industrial buildings.
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14. High Tensile Steel : Composition
Carbon – 0.8% (low carbon)
Manganese – 0.6%
Silicon – 0.2%
Sulphur – 0.05%
Phosphorus – 0.05%
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15. High Tensile Steel - Uses
High tensile steel is commonly used for Reinforced Concrete construction.
Used in Pre-stressed concrete.
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16. Types of Steel - based on its alloyed composition
Carbon steel
Alloy steel
Structural steel
Sheet steel
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17. Types of steel: Carbon Steel
Low carbon steel – less than 0.25% carbon
Medium carbon steel – 0.25% to 0.5% carbon
High carbon steel – over 0.5% carbon
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18. Types of Steel – Alloy steel
May include one or a combination of other minerals and metals.
For brittle steel, phosphorus, sulphur and silicone are added proportionately to the alloy.
For strength, nickel is added.
Hardness can be increased by adding manganese.
Resistance to corrosion can improve by adding Chromium and Copper.
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19. Types of steel – Structural Steel
Must be strong to hold structures and bridges.
Made in cold rolled or hot rolled methods.
Used for multi-storied buildings.
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20. Types of steel - Sheet Steel
Not more than 3mm thick.
Used for wall and roof cladding, curtain wall panels etc.
Available in mild steel, low alloy high strength steel and in stainless steel in maximum widths of 1830, 1520 and 1320 respectively.
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21. Mechanical Properties of steel depends on:
Chemical composition
Rolling methods
Rolling thickness
Heat treatment
Stress history
The most important mechanical properties of steel are its strength, elasticity and plasticity.
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22. Stress – Strain Diagram for Mild Steel and High Strength Steel
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23. Mechanical Test for steel
Tension
Bending
Hardness
Impact
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24. Tensile Test

25. Tensile Test
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26. Bending Test
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27. Hardness Test
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28. Impact Test
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29. Impact Test
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30. Protection of steel
Rusting is oxidation or combining of the iron with oxygen, which occurs in the presence of moisture.
Rusting proceeds more rapidly where there is noticeable dampness.
It occurs in any air with a relative humidity higher than 70 percent.
The rust is from the solid metal, reducing its size. The member becomes weaker. It loses any decorative finish it might have.
The rust penetrates deeper as time goes on.
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31. Preventing or Limiting Corrosion
Production of corrosion-resistant alloys.
Anodic metal coatings.
Chemical treatments.
Protective paintings.
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32. Production of corrosion – resistant alloys
Alloys are stable because a very coherent surface film of a compound of the metal, usually the oxide, forms of the surface.
Carbon steel more rust resistant by the addition of copper as alloying element.
Stainless steel have chromium and nickel as the their chief alloying elements. They contain 16 to 28 percent chromium and may contain up to 22 percent nickel. Stainless steel have high resistance to corrosion.
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33. Anodic metal coatings
A coating of metal which is anodic with respect to metal to be protected acts in two ways:
1. It excludes air and moisture.
2. If the coating is broken and a corrosion cell is set up, then corrosion of the cathodic metal will be inhibited. Metals commonly used to protect steel are zinc, aluminium and chromium coatings.
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34. Chemical treatment
Steel objects can be protected by dipping them in a bath of phosphoric acid. A stable film of iron phosphate is formed which protects the steel against corrosion.
The stability of the phosphate layer and hence the effectiveness of the protecting layer is increased by dissolving zinc or manganese phosphate in the bath of hot phosphoric acid.
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35. Protective Painting The protection provided by the paint is due to:
The presence of constituents called inhibitive pigments which suppress the anodic and cathodic reactions.
The slowing down of the movement of ions through the coat. Some cathodic protection is provided by pigmented paints.
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36. Different types of protective paints
Red lead in linseed oil.
Chromate metal primer.
Calcium plumbate metal primer.
Zinc pigmented paints.
Tar and bitumen paints.
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37. Corrosion
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38. Special Purpose Coating Systems – Hot Dip Galvanizing
Reasons for selecting Galvanizing -
For light fabrication and some medium structural applications, can be the lowest cost coating system.
Lowest long term cost coat coating system alternatives.
Galvanizing does not adhere to the steel, but is actually metallurgically bonded to the base forming an alloy layer between the surface zinc and the underlying base metal.
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39. Reasons for selecting Hot-Dip Galvanizing
Provides high resistance to mechanical damage in transport, erection and in service.
Galvanizing eliminates maintenance for relatively long periods of time.
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40. Stainless Steel - Advantages
Stainless steel is compatible with non-metals and metals. Washing will not stain adjacent materials.
Thermal movement is low and is also resistant to high temperatures.
Very hard and strong.
Good mirror like appearance.
Corrosion resistant.
Dirt can be washed off with plain water.
Do not have magnetic properties.
Good weldability.
Reasons for selecting Galvanizing
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41. Stainless Steel
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42. Fire Protection
Design of buildings fire protection is the major design consideration.
Three issues involved in fire protection – life safety, protection of the structure and fire suppression.
Compliance to building codes that specify the number of hours of fire exposure that a building structure must withstand, within specific temperature limits.
Building codes and the insurance underwriters determine fire suppression. Eg: Type of sprinkler systems.
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