What is a bar?

In civil engineering, bars refer to steel reinforcement bars or rebars. These are structural members primarily used for reinforcement purposes in masonry works. A bar is characterized by its cross-sectional area, which is negligible compared to its length. Bars are usually manufactured by steel which is uniform throughout the length, or by meshing multiple steel wires. Other materials of the bar include carbon steel, glass fiber, carbon fiber, and basalt fiber. The reinforcing bars are coated with epoxy resins and other materials to enhance some of their properties including corrosion resistance.

Purpose of bars

Rebars or steel reinforcement bars form the major component of masonry construction. Concrete is a brittle material that hardens due to hydration and the formation of new bonds. As a fundamental property of a brittle substance, they are very strong in compression but weak in tension. A structure merely made of concrete can withstand large compressive loads but under the influence of tensile loads, it fails drastically. To induce the property of tensile strength of the concrete, reinforcement is carried out. A reinforcement bar is primarily made of steel which is a ductile material, and ductile materials have superior tensile strength. Combining steel bars with concrete imparts concrete gains both compressive and tensile strength. Also, it accounts for resistance to shear deformations and thermal strains developed due to expansion and contraction due to temperature fluctuations.

Types of bars

There are different grades and thicknesses of bars and based on the application and construction criticality, an engineer chooses the right one. Bars are generally laid in a grip pattern with certain spacings of the grid. The spacing of the grid is very crucial in deciding the strength of the overall construction. Bars with variable thicknesses provide different strengths. The ridges provided on the periphery of the bars are provided to improve the bonding between the concrete and the bar.

There are various types of reinforcement bars used, based on the applications, some of them are outlined below.

Mild steel bars

Mild steel bars are characterized by their circular-cross section and plain periphery, they are very easy to bend and shape. These bars are available in a variety of thicknesses ranging from 6 mm to 50 mm and are specially used as dowels in expansion joints, for contraction joints in roadways and runways, and for making column spirals.

These bars are not suitable for the construction of heavy structures such as bridges and heavy buildings due to their plain periphery, which provides a very poor bond between the concrete and the bar.

There are generally three grades of mild steel bars, Grade I or Grade 60, Grade II or Grade 40, and medium tensile bars, designated as Grade 75.

Thermo Mechanically Treated (TMT) bars

The TMT bars have ribs, patterns, or lugs on their periphery which helps in securing a superior bond between the concrete and the bar. These bars eliminate the problems faced by mild steel bars. These bars are available in thickness ranging from 6 mm to 50 mm.

TMT bars are popularly used in reinforced concrete cement (RCC) works to provide superior strength. These bars are heat treated and provide high strength characteristics. Some of the properties of TMT bars are outlined below:

• Good ductility and weldability
• Good bond with concrete
• High yield strength and toughness
• High thermal resistance and malleability
• Earthquake and corrosion resistance
• Can be welded using ordinary electrodes

Epoxy coated bar

Epoxy-coated bars are similar to TMT bars in terms of strength and durability, but they are coated with epoxy resins which make them corrosion-resistant, which is 70 to 1,700 times more than ordinary TMT bars.

Stainless steel bar

These bars are the most expensive. They provide 1,500 time more corrosion resistance than other bars. These bars are made of stainless steel having high chromium and vanadium content with little carbon. These are the best choice for most civil engineering projects.

Carbon steel bar

These bars are known as black bars due to their high carbon content. They provide the best tensile strength to the concrete but are usually poor in providing resistance to corrosion.

Advantages of using rebars

The different advantages of using rebars are outlined below.

Concrete compatibility

All the bars are compatible with different varieties of concrete. Hence, a special checklist or specification is not necessary to match concrete and reinforcement bars. Simply, the fresh concrete is applied over the reinforcement mold created by the bars, which gains hardness over time.

Robustness of reinforcement

Reinforcement provides the structure with a huge degree of tolerance for loads and deformations. They provide the structure with strength and durability.

Malleability and workability

The steel bars are easily workable and can be bent into any desired shape, which makes them flexible in creating any kind of formwork.

Recycling

The leftover after construction can be easily recycled by melting in the furnace and re-extruded to create new reinforcement bars.

Easy availability

These bars are easily available in every corner of the world, and it is a fundamental raw material for construction.

Context and Applications

This topic is extensively taught in different undergraduate and postgraduate degree courses of:

• Bachelors in Technology (Mechanical engineering)
• Bachelors in Technology (Civil engineering)
• Masters in Science (Construction of building)
• Masters in Technology (Mechanical engineering)
• Masters in Technology (Civil engineering)

Practice Problems

Q 1. What is the full form of TMT?

a. Thermally molded and treated

b. Thermomechanical treatment

c. Thermomechanically treated

d. None of these

Answer: Option c

Explanation: The full form of TMT is Thermomechanically treated.

Q 2. Which of the following bars provides the highest corrosion resistance?

a. Epoxy-coated bar

b. TMT bar

c. Galvanized bar

d. Stainless steel bar

Answer: Option a

Explanation: Epoxy-coated bars provide the highest corrosion resistance.

Q 3. What is the purpose of reinforcement in concrete?

a. It induces high shear strength to the concrete.

b. It induces high corrosion resistance to the concrete.

c. It imparts high toughness to the concrete.

d. It induces high tensile strength to the concrete.

Answer: Option d

Explanation: Reinforcement imparts high tensile strength to concrete.

Q 4. What is the purpose of providing ridges on the surface of the bar?

a. To impart bending strength

b. To impart twisting strength

c. To impart superior bond with concrete

d. None of these

Answer: Ridges are provided on the surface of the bar to improve the bond with the concrete.

Q 5. Which of the following is a property of the TMT bar?

a. Weldability

b. Malleability

c. Workability

d. All of these

Answer: Option d

Explanation: TMT bars provide a variety of properties like weldability, malleability, and workability.