A deformed bar, commonly known as rebar (reinforcing bar), is a steel rod used as a tension device in reinforced concrete structures. Its surface features protrusions, such as ribs, lugs, or indentations (deformations), which create a strong mechanical bond and enhance friction with the surrounding concrete. 

Purpose and Function

Concrete is strong in compression but relatively weak in tension (pulling or stretching forces). Deformed bars are embedded within the concrete to bear these tensile stresses, thereby reinforcing the structure and preventing cracking or failure. 

The primary functions and benefits include:

Enhanced Bonding: The surface deformations provide a superior grip compared to smooth bars, preventing the bar from slipping within the concrete under load.

Increased Structural Integrity: This strong bond allows the steel and concrete to act as a single, composite unit, which significantly increases the overall strength, durability, and load-bearing capacity of the structure.

Crack Prevention: Deformed bars help distribute stress evenly throughout the concrete, which minimizes the occurrence and spread of cracks.

Seismic Resistance: The enhanced bond and ductility (ability to deform without sudden failure) are crucial in areas prone to earthquakes, as they allow the structure to withstand swaying motions and absorb significant energy. 

Types and Applications

Deformed bars are widely used in a variety of residential, commercial, and civil engineering projects, including:

Building foundations, columns, and slabs.

Bridges, roads, tunnels, and dams. 

Common types of deformed bars, primarily made from carbon steel, include:

Carbon Steel (Black Bar): The most common and versatile type, though susceptible to corrosion.

Epoxy-coated: Used in environments exposed to saltwater or high humidity due to its corrosion resistance.

Galvanized: Coated in zinc to be more resistant to corrosion than carbon steel.

Stainless Steel: The most expensive, but also the most corrosion-resistant option.