In reinforcement detailed drawings and bar bending schedules, you usually come across the following terms Concrete Cover, Clear cover, nominal cover and effective cover today I will answer all of your doubts regarding these terms, let’s dive in.
We consider the below Beam Cross-section in this article, to make you understand with these terms clearly.
Concrete Cover :
In reinforced concrete structures, the reinforcement is surrounded by the sufficient concrete cover to protect the concrete from atmospheric conditions which makes concrete to corrode.
The distance is measured in different ways, and these have different terms like Clear Cover, Nominal Cover and Effective Cover.
The clear cover is the distance between the exposed concrete surface (without plaster and other finishes) to the nearest surface of the reinforcing bar Look into the following image for more detail.
In the following picture, Clear cover is clearly illustrated.
As per IS 456(Clause 26.4.1), the term clear cover is replaced by the term Nominal cover. The nominal cover is the distance between the exposed concrete surface to nearest reinforcement bar ( it may be any bar main bar, longitudinal bar and even links or stirrups).
The nominal cover should not be less than the diameter of the bar.
Effective cover :
This term is usually used in design calculations. The effective cover is the distance between the exposed concrete surface to the centroid of the main reinforcement. (or)
The effective cover is the distance between the outermost compression face of RCC to the center of the area of main reinforcement in tension.
In the following image, d is the total diameter of the stirrup & D is the total diameter of the main reinforced bar, an. We all know centroid of the main reinforcement bar which means at the centre of the bar i.e., at D/2.
Hence effective cover = Clear cover + Total Diameter of Stirrup (d)+ (Diameter of main reinforcement bar (D))/2.
In the following image, effective cover is clearly depicted from the beam cross-section.
Clear Cover, Nominal Cover & Effective cover example:-
From the above Figure,
Diameter of Stirrups (d) =8mm,
Diameter of Main reinforcement (D) = 16mm
Clear Cover = 60mm
Effective cover = Clear cover + d + D/2
= 80mm + 8mm + 16/2 = 68mm + 8mm = 96mm
Now its time of yours to test yourself on Nominal Cover, Clear cover and Effective cover Can you Answer this?
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