Cover is the thickness of concrete measured from the nearest outer surface of reinforcement. Cover is mainly provided to protect the reinforcement bars. In RCC structure reinforcement provided in concrete upto a specific distance from the face of the member.
Purpose of Providing Cover:
1. To protect the reinforcement from corrosion.
2. To provide fire resistance to the reinforcement.
3. To provide adequate distance in order to develop required stress by reinforcement.
Clear cover is the distance between the outer surface of concrete to the nearest surface of reinforcing bar.
It can be defined as the distance measured from the face of member to the outermost face of the reinforcement including stirrups or links. Nominal cover is same thing as clear cover with a different name.
Effective cover is the distance measured from the face of the member to the center of area(centroid) of the main reinforcement. This is the dimension mostly used for design calculation.
Effective cover = Clear cover + Dia of stirrups/ links + 0.5 x Dia of main reinforcement bar.
Effective cover = Overall depth – Effective depth.
Here is another illustration,
d = effective depth.
c = clear cover.
x = effective cover.
The effective depth is measured from the face of the member to centre of area of main reinforcement.
Hence, Effective cover = Clear cover + (Dia of Stirrups/links) + (Dia of main reinforcement bars) + 0.5*(spacing between bars).