Structural Steel

Pankaj Sharma

Royal Member
Staff member
Steel is an alloy of iron and carbon. It has also other elements e.g. Silicon, Phosphorous and sulphur in varying percentage. Steel is generally manufactured by open hearth process., electric process, bessemer process, cementation process and L.D process.



Pure iron is very soft but when carbon is added to iron (chemically combined with iron), it forms iron carbide is known as cementite. The percentage of carbon in steel is the important factor in governing its properties and uses. More percentage of carbon will increase the strength of steel. The percentage of of carbon varies upto a maximum of 1.5% up to max. Level of 1.5%, all the carbons gets into the chemical combination with iron and none of its exists in its free state .

Main impurities in steel are silicon, phosphorous and sulphur.

  • Silicon from 0.3 to 0.4% in the steel, increases elasticity and strength of steel without much reduction in its ductility.
  • Phosphorous is harmful because it reduces the strength toughness and ductility of steel. The percentage of phosphorous in steel should be limited to 0.12%
  • Sulphur from 0.02 to 0.10% has no noticeable effect on the ductility and strength of steel. However too much of sulphur will decrease the strength and ductility of steel.


Mechanical properties of steel



Properties of steel that defines its behavior under applied loads are known as mechanical properties of steel. The important mechanical properties of steel are:
  • Elasticity: - Elasticity is the property of the material by virtue of which it regains its original size and shape on removal of the applied load. Structural steel should be elastic.
  • Plasticity: - Structural steel to be some extent should be plastic. Plasticity is the property of the material by virtue of which it retains the deformed shape even after removal of applied load. Plasticity is opposite to elasticity.
  • Ductility: - It is the property of the material by virtue of which it can be drawn into thin wires without braking or rupture application of tensile load. This property of steel is very important as it helps in the uniform distribution of the stresses and tries to reduce the stress concentration. Ductility of steel decreases when the percentage of carbon in steel increases. Ductility of materials due to the plasticity. Ductility can be measured by the percentage elongation and the percentage reduction of the area in tensile test before rupture of attest piece. The material having high values of percentage elongation and reduction in area and ductile materials.
  • Brittleness: - Lack of ductility is brittleness. Brittleness is the property of the material which causes its rupture with little or no plastic deformation. Brittleness increases with the increase the carbon percentage in steel but its ductility decreases.
  • Malleability: - It is the property of material by virtue of which it can be beaten or rolled in to the thin sheets without rupture. Malleability of material is due to the plastic deformation like ductility. However ductility is a phenomenon because of tensile stress whereas malleability is because of compressive stress. Malleability is generally Increases with increase of temperature.
  • Hardness: - It is the property of the material by virtue of which it can resist abrasion, indentation, machining and scratching. It is usually expressed in relation to the hardness of the other material. hardness decreases by heating.
  • Fracture toughness or toughness: - It is the property of the material by virtue of which it can be twisted, bent, or stretched under a high stress before rupture. It is measurement by the amount of energy that a unit volume of the material has absorbed after being stressed up to the point of fracture. The area under the stress-strain curve indicates the toughness. Toughness decreases when material is heated. The value of toughness is very useful in the selection of a material where impact loads are frequently applied.
  • Elastic Toughness: - It is also known as modulus of resilience. Elastic toughness is the amount of energy stored per unit volume of the stressed material when it is stressed to the elastic limit. It can be obtained from the area under the stress-strain curve within elastic limit.
  • Fatigue: - Failure of a material due to repeated application of a stress less than the ultimate stress is known as fatigue or fatigue failure. The maximum stress the at a material can withstand without failure for a specific no. of cycles of stress is called its fatigue or endurance limit.
  • Creep: - The continuous deformation of a material under a constant load at temperatures is known as creep.
Structural steel: The manufactured steel rolled to section and weight as specified by Bureau of Indian standard is called as Structural Steel.

The standard of structural steel of different qualities is:-

  • IS:226-1975(Standard quality)
  • IS:1977-1975(ordinary quality)
  • IS: 2062-1984(fusion welding quality)
  • IS: 961-1975(high tensile structural steel)
  • IS:8500-1977(weldable medium and high strength quality)
Standard quality steel (mild steel) is the most commonly used steel for general construction purposes of the buildings, bridges, transmission, line tower, industrial structure etc. For making structure in standard quality steel, riveting or bolting can be used for all the thickness equal to or smaller than 20mm only.



Advantages of steel as a structural Material:-

  • The steel members have high strength. Therefore, the steel member can resist heavy load with comparatively light weight and small size of members
  • The steel member can be conveniently handled and transported because of their small size.
  • Properly maintained steel structures have long life.
  • Addition and alteration can be made easily to steel structures.
  • The properties of steel mostly do not change with time. This makes the steel most suitable material for structure.
  • Steel, being a ductile material does not fail suddenly, But gives a visible evidence for impending failure by large deflections.
  • Steel member can be erected at the faster rate.
  • Steel has highest scrap value amongst all building materials.

  • The steel members are gas and water tight, because of high density of steel.
Disadvantages of steel structural material:-

  • The steel Members are costly
  • The steel members are susceptible to corrosion. Therefore, they require frequent painting.