Steel is probably the most versatile comnonly used structural material. Not only is its versatility apparent in great varlety of structures or which it is used but also in many different of structural steel of interest to the designer can be described by the behavior of steel during a simple tension test. The essential elements in steel are metallic iron element non-metallic carbon, with small quantities of other elements such as slicon nickel, manganese chromium and copper. It is thus an alloys.
Though steel is usually more than 98% iron, with other element present in same quantities, these other element have pronounced effect on the properties of steel. Various iron - carbon alloys used as structural material are of three types
(I) Cast iron
(I) Wrought iron
(Ill) Steel cast iron
Steel cast iron a low carbon content, while wrought iron has high carbon content. In many ways steels are intermediate in carbon content, between cast iron and wrought iron. The approximate limits for carbon in steel are between 0.04 to 2.25 percent, through the limits for carbon in structural steel are between 0.15 to 1.7 percent.
Cast Iron: Cast iron has low carbon percentage, which makes it very brittle.
Wrought Iron: Wrought iron has high carbon content, imparting it the ability to permit large deformations without fracture. Due to this quality, it replaced cast iron. The wrought iron could be formed into plates which can, in turn, be cut and shaped into structural member.
Steel: Steel has carbon content intermediate between cast iron and wrought iron. Depending upon the chemical composition, different types of steels are classified as
(I) Mild steel
(Il) Medium carbon steel
(III) High carbon steel
(IV) Low alloy steel and
(V) High alloy steel
Out of these, the first three types of steels are known as structural steel, commonly used in steel lstructures. Indian standard IS
800-2007 is applicable to the types of structural steels covered by the following Indian Standards.
1. IS:
226-1975 Structural steel (standard quality)
2. IS:
1977-1975 Structural steel (Ordinary quality)
4. IS:
8500-1977 Weldable structural steel (medium and high strength qualities)
Structural steel (Standard quality) IS :
226-1975Steel in this designated as St 44-SC with copper content varying from 0.2 to 0.35%. mild steel is used for manufacture of rolled steel sections, rivets and bolts. Steel conforming to IS :
226-1975 is suitable for all type of structures subjected to static dynamic and cyclic loading and is suitable for welding
upto 20 mm thickness. The physical properties of mild steels are as under
(I) Mass : 7.85 kg/cm² (7850kg/m²)
(II) Young's modulus of elastieity (E): 2.04 × 10⁵ MPa(or N/mm²)
(Ill) Modulus of Rigidity (G) 0.785 × 10⁵ MPa (or N/mm²)
(IV) Poisson's Ratio (p):03 (in elastic range)
(V) Coefficient of thermal expansion or contraction: 12 × 10-¹⁰ per⁰ C or 6.7 × 10-⁶ per⁰ F
Structural steel is rolled into a variety of shapes and sizes. The shapes are designated by the shape and size of their cross-section.
Following are various types of rolled structural steel sections commonly used
(l) Rolled steel beam section (l-section)
(II) Rolled steel channel sections
(IIIl) Rolled steel angle sections
(IV) Rolled steel T-sections
(V) Rolled steel bars
(VI) Rolled steel plates
(VIl) Rolled steel sheets and strips
(VIII) Mild steel flats
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