What is Structural Steel? Types and Properties

Properties of Structural Steel

The features of structural steel influence the design and construction of steel structures. The value of different steel characteristics is highlighted below. The various tests that produce the values of mechanical properties of structural steel and the desired values of each property have been discussed in this article.

• Density: Structural steel has a density of 7750 to 8100 kg/m³. 
• Young's Modulus of Elasticity: Typical values for structural steel range from 190-210 GPa
• Poisson's ratio: For structural steel, the acceptable value ranges from 0.27 to 0.3.
• Tensile strength: Structural steel has high tensile strength so it is preferred over other materials for construction.
• Yield strength: The yield strength, also known as the yield point, is the stress at which an object permanently deforms. When stress is removed, it does not revert to its former shape. Carbon structural steel has a yield strength ranging from 187 to 758 MPa. The values of structural steel constructed of alloys range from 366 to 1793 MPa.
• Shear strength: The shear strength of steel structure is specified at the failure under shear stress and it is about 0.57 times the yield stress of structural steel.
• Hardness: The resistance of an object to shape change when force is applied is referred to as hardness. There are three different types of hardness tests. Scratch, indentation, and rebound are all terms used to describe the process of scratching, and indenting, and the hardness of structural steel manufactured with alloys ranges from 149 to 627 kg. Carbon structural steels have a weight range of 86 to 388 kg.
• Melting point: Because there are so many different types of structural steel, there is no standard melting point.
• Specific heat: The amount of heat required to raise an object's temperature by a particular quantity is known as specific heat or heat capacity. A higher specific heat value indicates that the object is more insulating. The units of measurement are Joules per Kilogram Kelvin. Specific heat for carbon structural steel ranges from 450 to 2081 J/kg-K, while for alloy structural steel it ranges from 452 to 1499 J/kg-K.

Types of Structural Steel

Carbon is the most often used commercial steel alloy. Increased carbon content improves hardenability and boosts hardness and strength. Carbon, on the other hand, increases brittleness and lowers weldability because of its proclivity for forming martensite. As a result, the carbon content in commercial steel can be both a blessing and a burden. Based on the carbon content, the mechanical properties of different types of structural steel and their uses are given below:  

• Carbon steel: Steel in which the carbon content is upto 2% is known as carbon steel. The Specified ultimate tensile strength is 410 to 440 MPa and the yield strength is 350 to 400 MPa.
• High strength carbon steel: These steels are used in structures such as transmission lines and microwave towers. The specified ultimate tensile strength is 480 to 550  MPa, and the yield strength is 350 to 400 MPa.
• Medium and high strength micro-alloyed steel: Alloys such as chromium, nickel, and molybdenum, etc are used to increase the strength while retaining the desired ductility. The specified ultimate tensile strength is 440 to 590  MPa, and the yield strength is 300 to 450 MPa.
• High strength quenched and tempered steel: In this type of Steel, heat treatment is done to develop high strength. The specified ultimate tensile strength is 440 to 590  MPa, the yield strength is 300 to 450 MPa.
• Weathering steel: These are corrosion-resistant Steel and are often not Painted. The specified ultimate tensile strength is 480 MPa, and the yield strength is 350 MPa.
• Fire-resistant steel: These steels are also known as thermo mechanically treated (TMT) steel and are used where the structures are more prone to fire.

Types of Steel Sections

Structural steel members are fabricated in factories according to their intended use. Continuous casting moulds are used to cast rolled steel parts with no joints. The following sections describe the various shapes and forms of rolled steel sections.

1. Rolled Steel I-sections (Beam sections).
2. Rolled Steel Channel Sections.
3. Rolled Steel Tee Sections.
4. Rolled Steel Angles Sections.
5. Rolled Steel Bars.
6. Rolled Steel Tubes.
7. Rolled Steel Flats.
8. Rolled Steel Sheets

Rolled Steel I- sections

Used as beams or columns.

Beams

ISJB – Indian Standard Junior Beam

ISLB – Indian Standard Light Beam

ISMB – Indian Standard Medium Beam

ISWB – Indian Standard Wide Flange Beam

Columns/Heavy weight beams

ISSC – Indian Standard Column Section

ISHB – Indian Standard Heavy Beam                                   

Rolled Steel Channel Sections

Used in steel-framed structure, steel bridges, crane girders

Categories – 

  ISJC - Indian Standard junior channels

  ISLC - Indian Standard lightweight channels

ISMC - Indian Standard Medium Weight Channel.

ISMCP - Indian Standard Medium weight parallel flange channels

Rolled Steel T - Sections

Used to form built-up sections and as members of steel roof trusses.

Categories-

ISNT - Indian Standard Normal Tee Bars

ISHT - Indian Standard Wide flange Tee Bars

ISST - Indian Standard Long Legged Tee Bars

ISLT - Indian Standard Light Tee Bars

ISJT - Indian Standard Junior Tee Bars

Rolled Steel Angle Sections

Used in the construction of roof trusses and filler joist flooring.

Categories-

ISA - Indian Standard Equal Angles

ISA - Indian Standard Unequal Angles

ISBA - Indian Standard Bulb Angles           

Rolled Steel Bars

Used as reinforcement in concrete and steel grill work, among other things.

ISRO – Indian Standard Round Bars         

Rolled Steel Tubes

Used in tubular trusses as columns, compression members, and tension members.        

Rolled Steel Flats

Lattice bars made of rolled steel flats are used to connect the elements of built-up columns.

Rolled Steel Sheets

These are used in automobiles, appliances, furniture, and many other everyday items.

Uses of Structural Steel

Structural steel is the most widely used engineering and building material on the planet. It is widely being used in modern construction. Because of its constructability and high strength-to-weight ratio, structural steel is used to build today's highest structures. 

Concrete, on the other hand, has a substantially lower strength-to-weight ratio than steel, although being less dense. This is owing to the substantially larger volume necessary for a structural concrete element to hold the same weight; steel, although denser, requires less material to carry the same load. 

Building Works 

• As a structural component in trusses, beams, and other steel structures.
• Grills, doors, windows, and other non-structural materials
• In steel pipelines, tanks, and other similar structures.
• In sanitary and sewer fittings, as well as rainwater items, and so on.
• Sheets are made of corrugated cardboard.
• As a concrete reinforcement.

Reinforcement Works

Since the concrete is strong in tension and weak in compression, steel is used as reinforcement to increase the tensile strength of the concrete structure.

Composition of Structural Steel

The chemical compositions influence the properties of Structural steel, some chemical elements used to enhance the mechanical properties are listed below.  Structural steel is a mixture of iron and other metals.  Some elements are purposefully added to iron in order to achieve specific properties and features, the various compositions have been discussed in the following:

• Carbon: One of the most significant chemical ingredients in steel is carbon. Carbon concentration rises, resulting in a material with less ductility and more strength.
• Chromium: Small levels of chromium are present, and it is combined with copper and nickel to strengthen the material's corrosion resistance.
• Manganese: Manganese, along with oxygen and sulphur, is employed as a neutralizer in the hot rolling of steel, and it has effects on the material properties of steel grades that are similar to those of carbon.
• Aluminum: Aluminum is a key deoxidizer that contributes to the formation of a finer-grained crystalline microstructure.
• Copper: Copper is used to promote corrosion resistance.
• Sulphur and phosphorus: Sulphur and phosphorus are often limited in steel alloys because they have negative impacts on the steel's durability and strength.
• Molybdenum: Molybdenum increases the steel's strength at high temperatures while also increasing its corrosion resistance.