The structural elements in the buildings are having the internal forces namely compression, tension, bending moments and torsion. Withstanding these internal forces with low tendency for collapse and any undesirable deformation for serviceability condition is the main task of the construction materials.
Concrete is generally preferable as a construction material over other alternatives as it is an economical solution to the construction industry. The compression strength of the concrete is much higher than any other materials whereas its tensile strength is so weak. In order to get the maximum usage of the compression strength of the concrete, the steel is integrated into the concrete to takeout the tension acting in the structural elements. Thus, the tensile capacity of the structure is also higher as the compression capacity. This integrity of steel into concrete is named as Reinforced Concrete, and that steel is referring as Reinforcement or Reinforcement Steel or Reinforcing bar (Rebar) or Reinforcing steel.
Why steel as Reinforcement?
There are so many options available to use as the reinforcement with concrete. Even though some properties of the steel which are compatible with concrete made the choice as steel over other materials. The thermal coefficient of the steel and concrete are similar. Also, it does not need any special tie up during the placement of concrete as it will not float over the concrete. Easy fabrication, recyclable and better bendability at site without detrimental effects in the section are made it as a choice over other materials.
On the other hands, the corrosive nature and expense of the steel are some disadvantages of the steel. The surface of the steel is deformed (ribs) to have a better bonding surface with the concrete.
Usage of Steel in Reinforced Concrete
- Primary Reinforcement
This is the main reinforcement provided to the structural element to resist the tensile stresses arising in the element due to the loads. In some cases, it is also used as a compression reinforcement, thus the concrete volume can be reduced to maintain the clear spaces for architectural purposes.
- Secondary Reinforcement
In addition to the primary reinforcement, secondary reinforcement provides an additional resistance in case of thermal expansions and it limits the crack developments thus preserves the aesthetic of the elements.
- Links and stirrups
Again the steel is in use to control the shear forces arising on the structure due to the external loads. Usually 6mm, 8mm, 10mm and 12mm links are used for beams. In case of deep beams, where the existence of high possibility of torsional effects, 16mm links will be used.
- Chairs or stools
Miscellaneous use of steel in the reinforced concrete structures are stools which are used to maintain the gap between top and bottom reinforcement.
Types of Rebar
Carbon steel is the typical steel used in the reinforced concrete. It can be classified into two primary categories.
- Hot-rolled Steel Bar
- Cold-formed Steel Bar
- Mild Steel Plain Bar
- Prestressing Steel Tendons