Steel is a very important construction material used in construction. There are different forms and shapes of steel found in the market. Different forms of steel are used to construct the structure in different places like roofs, windows, doors, gates, etc.
Similarly, a steel rebar is used to construct the heavy structure of concrete. Here we will discuss different types and different forms of steel used for construction.
Different Types of steel
1. Reinforcement steel
Reinforcement is the process by which a material is used in combination with another material to take up a particular type of load. Concrete members of the structure are reinforced with steel elements at places where the members are subjected to tensile stresses.
Mild steel is extensively used as a reinforcing material with concrete. Reinforced bars are often bent into shapes; therefore they should have adequate formality to have bending characteristics.
Reinforcing bars are available in various sections like flats, square bars, plain round bars or deformed bars, among which round bars are most extensively used. Welded wire mesh and expanded metal too are used as reinforcement in cement concrete.
2. Steel alloys
When certain special properties have been desired some elements such as sulphur, phosphorous, manganese, etc. are added to the carbon steels. These steel thus obtained are called alloy steels. The alloying elements are added to accomplish one or more of the following:
✓ To improve the fine grain size of steel
✓ To improve case hardening properties
✓To improve elasticity
✓ To improve corrosion and fatigue resistance
✓ To improve hardness, toughness and tensile strength
✓ To improve machinability
3. High tensile steel
This is an alloy of steel containing carbon up to 0.12 %. Other ingredients are : Manganese – 0.35 %
Nickel – 0.55 %
Silicon – < 0.75 %
Copper – 0.4 %
Chromium – 1 %
Sulphur- < 0.05 %
It has a high tensile strength of 6000 kg / cm2 whereas the maximum tensile strength of other types of steel is only up to 4500 kg / cm2. Uses wire – rope, pre-stressing cable.
4. Stainless steel
Stainless steel is an alloy containing 18 % chromium, 8 % nickel and iron with a small percentage of carbon, manganese, silicon, phosphorous and sulphur. It is resistant to corrosive attacks and atmosphere temperatures. It is manufactured in a wide range of brands, each having distinct chemical composition as well as different physical properties.
Properties of stainless steel
✔ Silvery white in appearance
✓ Ductile, hard, strong and tough
✔ High corrosion resistance
✓ Easy weldability
✓ Thermal and electrical conductivity is low
✓ Be polished to a mirror finish
✓ The carbon content is usually less than 0.10 %
Uses of stainless steel
Chemical vessels, containers for acid materials, surgical instruments, hardware material, auto parts, household goods, knives, blades, welding rods for welding other stainless steel, etc.
Market forms or shapes of steel
1) Round bars
These are circular sections with varying diameters ranging from 5mm to 250mm. Commonly used sections are of 5mm to 50mm diameters. Usual lengths are from 10m to 12m.
These are widely used as reinforcement in RCC works and in RB work and for fabricating Grills and Railings. Bars of less than 5mm diameters are termed wires.
2) Square bars
These are square sections; followed by the side width of the sections in mm. Sizes vary from 5mm square to 250mm square. These are commonly used for grillwork and railings in buildings. II.
3) Deformed bars
These bars have projections on their surfaces that increase their bond with concrete in RCC. Permissible tensile stress in these bars is about 50 % more than in MS bars. Deformed bars could be cold twisted or hot rolled. Hot-rolled bars are ribbed type and its common trade name is tor steel.
4) Flats steel
Commonly termed mild steel flats; are available from 5mm x 250mm in section and 6.5 m long. In structures, these are used for fabricating grills and railings.
5) Angle sections
This section has two legs, one vertical and another horizontal. Both the legs. are of the same thickness. If both the legs are of the same length then it is termed equal and if the length of each of the two legs differs then it is termed an unequal angle.
These are extensively used in the fabrication of roof trusses, steel frames for doors and in the fabrication of other built-up structural sections.
6) T sections
This section resembles the Roman alphabet T in shape. The top horizontal portion is called the flange and the vertical portion meeting the flange at its midpoint is termed a web. These are extensively used in roof trusses and in fabricating built-up sections.
7) I section steel
The section resembles the Roman alphabet I in shape. The top and the bottom horizontal portions are termed flanges and the vertical portion joining the midpoints of the two flanges is termed a web.
These sections are termed as-rolled steel joists too. These are extensively used as floor beams, as columns and in fabricating built-up sections like stanchions.
8) Channel sections
These sections have two horizontal portions, termed flanges connected to each other at ends by a vertical member termed a web. These are mainly used to build up different structural sections.
9) Steel Plates
Steel plates are rolled to thickness varying from 5mm to 63mm, width 900mm to 2500mm and length used from 2200mm to 12500mm. These are fabricating built-up structural sections.
10) Corrugated sheets
Corrugated sheets have a cross-section of sine curves to give strength, rigidity and stiffness to the sheets. These sheets are protected against corrosion by galvanizing ( giving a coating of zinc ) and are called galvanized corrugated iron sheets or CGI sheets.
Galvanized iron sheets without corrugations are abbreviated as GI sheets. Corrugated GI sheets are 66cm wide and up to 3m long. Thickness varies from 24 gauge to 16 gauge.
11) Welded wire fabrics
Welded wire fabrics are maintained in sheets and rolls and are available in the rectangular or square mesh of sheet wires with various diameters. The cross wires which make the fabrics are electrically welded, ensuring correct spacing of cross wires and rigidity of welds.
It is extremely versatile and lends strength, safety and style to buildings when used for verandah enclosures, windows, fences, partitions and gates. It is also used as reinforcement in RCC slabs.
12) Expanded metals
It is manufactured from mild steel or plates in various sizes and thicknesses, which are machine cut and drawn out or expanded.
A diamond mesh appearance is thus obtained throughout the whole area of the sheet. Expanded metal is widely used for reinforcing concrete in foundations, roads, floors, bridges, partitions, etc. These are also used as fencing.
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