R.C.C i.e. Reinforced Cement Concrete.
RCC is nothing but the Reinforced cement concrete. Reinforced cement concrete is concrete which has reinforcement in it. Any Flexural Member or Spanning Member (Simple Supported) is subjected to Compression above the Neutral Axis and Tension below the Neutral Axis. Concrete is good in compression but poor in tension as can be seen from the properties of Concrete. Concrete has limited Shear Strength too. And that is the reason why we provide the structural steel at bottom section i. e below neutral axis.
Maximum Tensile Strength (fct) in Concrete is given by,
fct = 0.7√fckN/mm² i.e. 3.13N/mm² in case of M20 Grade Concrete.
Sometimes fct is also denoted as fcr to symbolize the cracking in concrete due to poor tensile resistance.
The Tensile Strength is also known as Flexural Cracking Strength.
This makes Concrete a poor material for Spanning or Bending Members subjected to Compressive and Tensile Stresses. Hence we reinforce the Concrete by a small quantity of Steel in the appropriate areas to take care of these Tensile Stresses. This is Reinforced Cement Concrete.
Generally this reinforcement is provided in the form of Round Bars of Various Diameters
Why Steel is used in RCC?
1. Steel Forms an excellent Bond with concrete. They act like one material in a Composite Material.
2. Steel and concrete have approximately same Thermal Coefficients of expansion, thus keeping the
structure uniform during temperature variations. Steel also bears the tensile forces generated while the
concrete expands thermally during fire or other temperature rise.
3. Steel has High Tensile Strength and is easily available in the form of Round Bars
4. Steel bears Compressive Stresses too. That’s a bonus!
5. Steel together with concrete results in stability of the structure within affordable costs.
This is the reasons why steel is used in RCC. Concrete is good in compression but poor in tension as can be seen from the properties of Concrete. Concrete has limited Shear Strength too. And that is the reason why we provide the structural steel at bottom section i. e below neutral axis.
Alternative materials for steel???
Yes there is many alternative materials for steel. but we always choose mild steel for the RCC and steel construction:
- Cast Iron: Cast iron has carbon content upto 2.1%. Carbon in steel is responsible for strength and brittleness. More the carbon, more strengthen and the brittle the materials is. And we do not want brittleness in construction as RCC is already britttle. if we provide the cast iron the element will fail without any warning (Deflection) and hence not best alternative materials for steel
- Wrought iron:It has carbon less that 0.15% in it. so low carbon means low strength and low brittleness that means more ductility. here the strenght is very less that the mild steel, and if wroght irom is used in construction, we will end up using more steel, and that will become uneconomical and hence not best alternative materials for steel.
- Mild steel: Carbon content in mild steel is between 0.12% to 0.15%. so it has more strenght that wroght iron and more ductility than the cast iron. And it proved economical to use in RCC as well as steel structure.
- Aluminium: Aluminium is also a great option for steel but the problem with aluminium is that is has the elasticity 3 times less than the mild steel. Due to this reason we generally use aluminium is only partition wall (non load bearing) and hence not best alternative materials for steel.
- Chromium: Mild steel has corrosion property and hence maintenance needed. Chromium does not corrode easily. So it can be used to replacement with steel. but it so expensive than the steel. and hence not best alternative materials for steel.
- Metal alloys: For any particular construction special steel structure, the combination of 2 or more than two metal is used together to form new. in this way we can minimizes the cons for particular materials. and hence best alternative materials for steel.
- bamboo: Recently, bamboo is widely used in the construction as a replacement to steel, it has so many properties simillar to steel. and best alternative materials for steel. The construction with bamboo reduces the cost upto 40%. but here the problem with bamboo is,
The number of floor restriction: As per the study, we can use bamboo replacement to steel only upto G+1 structures (RCC only)
The durability: The self life of bamboo constructed building is almost 25-30 years, which is less than the steel used building.
Type of steel on the basis on their function:
1. To carry Direct or Bending Tension as in case of Beams, Slabs and Walls of water tanks. Such Steel is known as Main Steel, this being the primary function of reinforcement. This Steel is provided on the
Tension Face as far away from the Neutral Axis as possible with minimum Cover.(Explained Later)
2. To Distribute Load along the longer span in a slab, also to bind the Main Steel and keep it in position, take care of Temperature Stresses and Shrinkage in Concrete. This is provided in the form of Temperature or Distribution Steel of bars of smaller diameter generally in a Uniform mesh transverse to Main Steel. This Steel also prevents Cracks in Concrete
3. To Strengthen the Concrete to resist Compression as in the case of Columns. This Steel is called Main Steel or Longitudinal Bars located at corners and running Longitudinally along the faces
4. To Prevent Buckling of Longitudinal Bars in a Column and this is provided in the form of Links or Lateral Ties or Spirals.
5. To Resist Diagonal Tension due to Shear, To Resist Shear and to hold Main steel in Position like in Beams. These are called Shear Stirrups